ABCMdb

ABCC6 p.Arg1268Gln

ClinVar:	c.3803G>A , p.Arg1268Gln ? , Conflicting interpretations of pathogenicity
LOVD-ABCC6:	p.Arg1268Gln D
Predicted by SNAP2:	A: D (80%), C: D (91%), D: D (91%), E: D (75%), F: D (95%), G: D (91%), H: D (66%), I: D (80%), K: D (66%), L: D (85%), M: D (91%), N: D (75%), P: D (95%), Q: D (53%), S: D (80%), T: D (80%), V: D (75%), W: D (85%), Y: D (91%),
Predicted by PROVEAN:	A: D, C: D, D: D, E: D, F: D, G: D, H: N, I: D, K: N, L: D, M: D, N: N, P: D, Q: N, S: D, T: D, V: D, W: D, Y: D,

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[hide] Polymorphisms of MRP1 (ABCC1) and related ATP-depe... Pharmacogenet Genomics. 2005 Aug;15(8):523-33. Conseil G, Deeley RG, Cole SP
Polymorphisms of MRP1 (ABCC1) and related ATP-dependent drug transporters.
Pharmacogenet Genomics. 2005 Aug;15(8):523-33., [PMID:16006996]

Abstract [show]
Genetic variations in drug metabolizing enzymes and targets are established determinants of adverse drug reactions and interactions, but less is known about the role of genetic polymorphisms in membrane transport proteins. MRP1 (ABCC1) is one of 13 polytopic membrane proteins that comprise the 'C' subfamily of the ATP-binding cassette (ABC) superfamily of transport proteins. MRP1 and related ABCC family members, including MRP2, 3, 4 and 5 (ABCC2, 3, 4 and 5), each have a distinctive pattern of tissue expression and substrate specificity. Together, these five transporters play important roles in the disposition and elimination of drugs and other organic anions, and in maintenance of blood-tissue barriers, as confirmed by enhanced chemosensitivity of respective knockout mice. Moreover, Mrp2 (Abcc2) deficient animals display mild conjugated hyperbilirubinemia, corresponding to a human condition known as Dubin-Johnson syndrome (DJS). Naturally occurring mutations in MRP/ABCC-related drug transporters have been reported, some of which are non-synonymous single nucleotide polymorphisms. The consequences of the resulting amino acid changes can sometimes be predicted from in vitro site-directed mutagenesis studies or from knowledge of mutations of analogous (conserved) residues in ABCC proteins that cause DJS, Pseudoxanthoma elasticum (ABCC6), cystic fibrosis (CFTR/ABCC7) or persistent hyperinsulinemic hypoglycemia of infancy (SUR1/ABCC8). Continual updating of databases of sequence variants and haplotype analysis, together with in vitro biochemical validation assays and pharmacological studies in knockout animals, should make it possible to determine how genetic variation in the MRP-related transporters contributes to the range of responses to drugs and chemicals observed in different human populations.

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56 In the kidney, glomeruli and distal collecting tubules express MRP1, and, in the brain, MRP1 appears to form part of the drug permeability barrier Fig. 1 CF (CFTR/ABCC7) Q1291R E1228G Q1238R G1244E/V G1247R G1249R S1251N S1255P/L W1282G/R/C R1283K/M N1303K Y1307C E1321Q K1351E Q1352H R1268Q V1298F T1301I G1302R A1303P R1314W/Q G1321S R1339C Q1347H I1350L G1354R D1361N Q1382R A1450T R1347E R1351P V1359G/M S1368A G1377R G1382S R1392H R1419C R1435Q G1477R G1479R R1492W E1505K DJS (MRP2/ABCC2) NBD1 NBD2 COOH MEMBRANE MSD MSD MSD 12131415161710116 7 8 91 23 4 5TM H2 N Extracellular Intracellular PXE (ABCC6) PHHI (SUR1/ABCC8) Two-dimensional structure of MRP-related proteins. Login to comment

[hide] Pseudoxanthoma elasticum: mutations in the MRP6 ge... Proc Natl Acad Sci U S A. 2000 May 23;97(11):6001-6. Ringpfeil F, Lebwohl MG, Christiano AM, Uitto J
Pseudoxanthoma elasticum: mutations in the MRP6 gene encoding a transmembrane ATP-binding cassette (ABC) transporter.
Proc Natl Acad Sci U S A. 2000 May 23;97(11):6001-6., 2000-05-23 [PMID:10811882]

Abstract [show]
Pseudoxanthoma elasticum (PXE), the prototypic heritable connective tissue disorder affecting the elastic structures in the body, manifests with cutaneous, ophthalmologic, and cardiovascular findings, with considerable morbidity and mortality. The molecular basis of PXE has remained unknown, but the disease locus has recently been mapped to an approximately 500-kb interval on chromosome 16p13.1, without evidence for locus heterogeneity. In this study, we report pathogenetic mutations in MRP6, a member of the ABC transporter gene family, in eight kindreds with PXE. The mutation detection strategy consisted of heteroduplex scanning of coding sequences in the MRP6 gene, which were amplified by PCR by using genomic DNA as template, followed by direct nucleotide sequencing. A total of 13 mutant MRP6 alleles were disclosed in the eight probands with PXE. These genetic lesions consisted of either single base pair substitutions resulting in missense, nonsense, or splice site mutations, or large deletions resulting in allelic loss of the MRP6 locus. Examination of clinically unaffected family members in four multiplex families identified heterozygous carriers, consistent with an autosomal recessive inheritance pattern. Collectively, identification of mutations in the MRP6 gene provides the basis to examine the pathomechanisms of PXE and allows development of DNA-based carrier detection, prenatal testing, and preimplantation genetic diagnosis in families with a history of this disease.

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75 The mutation in exon 27 resulted in substitution of a codon for arginine by a codon for glutamine (R1268Q). Login to comment
77 MRP6 mutations in families with PXE Family Age and sex of proband Mutation Exon Consequence Verification* 1 53 F 3421C 3 T 24 R1141X BsiYI 3803G 3 A 27 R1268Q BstXI 2 29 F 3412C 3 T 24 R1138W MspI 3 40 F 3421C 3 T 24 R1141X BsiYI Partial deletion 24† Allelic loss D16S2720 MRP6 D16B9622 4 53 F 3736-1G 3 A 27 Altered splicing of exon 27 AciI Partial deletion 27† Allelic loss D16S2720 MRP6 D16B9622 5 60 M 3413G 3 A 24 R1138Q MspI 3803G 3 A 27 R1268Q BstXI 6 28 F 3421C 3 T 24 R1141X BsiYI 7 41 M 3803G 3 A 27 R1268Q BstXI 8 25 F 3421C 3 T 24 R1141X BsiYI *Mutations were verified in the proband and his/her family members by digestion with restriction enzyme, or in case of deletion, by microsatellite markers indicated. Login to comment
142 Evaluation of their DNA revealed that the patient in family 5 was compound heterozygous for nucleotide substitutions 3413G3A and 3803G3A in exons 24 and 27, which resulted in the amino acid substitutions R1138Q and R1268Q, respectively. In families 6-8, heterozygous nucleotide substitutions were discovered, resulting in the mutations R1141X (families 6 and 8), and R1268Q (family 7). Login to comment
159 Although only one mutation in each of the latter three individuals was observed, it is likely that PXE in these cases was also autosomal recessive, because each of the two distinct mutations (R1141X and R1268Q) discovered in these three probands were also present in the multiplex families, and the heterozygous carriers did not show definitive signs of the disease. Login to comment

[hide] Homozygosity for the R1268Q mutation in MRP6, the ... Biochem Biophys Res Commun. 2000 Aug 2;274(2):297-301. Germain DP, Perdu J, Remones V, Jeunemaitre X
Homozygosity for the R1268Q mutation in MRP6, the pseudoxanthoma elasticum gene, is not disease-causing.
Biochem Biophys Res Commun. 2000 Aug 2;274(2):297-301., 2000-08-02 [PMID:10913334]

Abstract [show]
Pseudoxanthoma elasticum (PXE) is an inherited systemic disorder of connective tissue, characterized by progressive calcification of the elastic fibers in the eye, the skin, and the cardiovascular system, resulting in decreased vision, skin lesions, and life-threatening vascular disease, with highly variable phenotypic expression. The PXE locus has been mapped to chromosome 16p13.1, and was recently further refined to a 500 kb-region, containing two pseudogenes and four candidate genes. In a comprehensive mutational screening, we were able to exclude the responsibility of pM5, UNK, and MRP1 genes, candidate on the basis of their genetic localization. Conversely, we have found pathogenetic mutations in the MRP6 gene, in patients affected with PXE, indicating that human MRP6, which encodes a 1503 amino-acids membrane protein, member of the human ATP binding cassette (ABC) transporters superfamily, is the gene responsible for PXE. In one large PXE pedigree for which we had identified a nonsense mutation (R1141X), we came across a G to A transition at position 3803 of the MRP6 cDNA sequence (R1268Q). Astonishingly, this latter variant was found at the homozygous state in the proband's unaffected husband. We investigated the R1268Q mutation, and found the Q1268 allele at a relatively high frequency (0.19) in a Caucasian control population (n = 62 subjects). Genotype frequencies were in Hardy-Weinberg equilibrium, and three healthy volunteers were homozygous for the Q1268 allele. These data indicate that the R1268Q variant in the MRP6 gene does not cause PXE per se. Further studies will elucidate if it may play a role when found in compound heterozygotes.

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0 Homozygosity for the R1268Q Mutation in MRP6, the Pseudoxanthoma Elasticum Gene, Is Not Disease-Causing Dominique P. Germain,1 Je´roˆme Perdu, Ve´ronique Remones, and Xavier Jeunemaitre De´partement de Ge´ne´tique, Hoˆpital Europe´en Georges Pompidou, Universite´ Paris VI, Paris, France Received June 13, 2000 Pseudoxanthoma elasticum (PXE) is an inherited systemic disorder of connective tissue, characterized by progressive calcification of the elastic fibers in the eye, the skin, and the cardiovascular system, resulting in decreased vision, skin lesions, and life-threatening vascular disease, with highly variable phenotypic expression. Login to comment
4 In one large PXE pedigree for which we had identified a nonsense mutation (R1141X), we came across a G to A transition at position 3803 of the MRP6 cDNA sequence (R1268Q). Login to comment
6 We investigated the R1268Q mutation, and found the Q1268 allele at a relatively high frequency (0.19) in a Caucasian control population (n ‫؍‬ 62 subjects). Login to comment
8 These data indicate that the R1268Q variant in the MRP6 gene does not cause PXE per se. Login to comment
18 During our molecular analysis of the MRP6 gene in PXE patients, we came across a G to A transition at position 3803 of the cDNA sequence, altering the codon (CGG) for arginine to the codon (CAG) for glutamine (R1268Q) in a pedigree in which we had previously identified a nonsense mutation (R1141X). Login to comment
19 In the present study, the R1268Q mutation was investigated in relatives of our PXE patients and in a control population, to determine if this amino-acid change was a disease-causing mutation or a neutral polymorphism. Login to comment
39 Mutation R1268Q predicted the creation of a novel restriction site for BstX I. Login to comment
42 Mutation R1268Q also predicted the loss of a Msp I restriction site. Login to comment
51 This nucleotide substitution alters the codon (CGG) for arginine to the codon (CAG) for glutamine (R1268Q). Login to comment
52 Restriction digests using BstX I, performed to examine family relatives, showed that both affected patients (II-3 and II-5) and their asymptomatic mother (I-2) were heteroallelic for R1268Q at the genomic level, the father (I-1) being a wild type homozygote. Login to comment
53 However, the proband`s asymptomatic husband (individual II-6 in Fig. 1) was found to be homozygote for R1268Q, ruling out a causative role for homozygosity for this mutation in the clinical phenotype observed in PXE patients. Login to comment
54 Mutation R1268Q also predicted the loss of a Msp I restriction site. Login to comment
57 The R1268Q mutation was identified in 24 of the 124 tested alleles, and its overall frequency was 0.19 (Fig. 3). Login to comment
60 Our results indicate that the R1268Q mutation in the MRP6 gene is a neutral polymorphism, which does not cause pseudoxanthoma elasticum when present at the homozygous state. Login to comment
66 During our mutational scanning of the MRP6 gene, in two sisters affected with pseudoxanthoma elasticum, a G to A transition, was detected at position 3803 of the MRP6 cDNA sequence, predicting a R1268Q missense mutation at the protein level. Login to comment
98 We have therefore investigated the R1268Q substitution to determine its frequency, and have found its frequency to be high in a Caucasian control population. Login to comment
100 It is interesting to note that the authors also detected the R1268Q mutation in their patients population, although always in the context of compound heterozygosity. Login to comment
101 Whether the R1268Q mutation may lead to the clinical phenotype observed in patients with PXE, when found in association with another, potentially more severe, mutation in the MRP6 gene remains to be elucidated. Login to comment
103 In conclusion, while screening the MRP6 gene in patients affected with PXE, we have identified, beside disease-causing mutations, a 3803G Ͼ A transition (R1268Q) which was shown to be a harmless polymorphism when present at the homozygous state. Login to comment

[hide] Compound heterozygosity for a recurrent 16.5-kb Al... Am J Hum Genet. 2001 Mar;68(3):642-52. Epub 2001 Feb 9. Ringpfeil F, Nakano A, Uitto J, Pulkkinen L
Compound heterozygosity for a recurrent 16.5-kb Alu-mediated deletion mutation and single-base-pair substitutions in the ABCC6 gene results in pseudoxanthoma elasticum.
Am J Hum Genet. 2001 Mar;68(3):642-52. Epub 2001 Feb 9., [PMID:11179012]

Abstract [show]
Pseudoxanthoma elasticum (PXE) is a systemic heritable disorder affecting the elastic structures in the skin, eyes, and cardiovascular system, with considerable morbidity and mortality. Recently, mutations in the ABCC6 gene (also referred to as "MRP6" or "eMOAT") encoding multidrug-resistance protein 6 (MRP6), a putative transmembrane ABC transporter protein of unknown function, have been disclosed. Most of the genetic lesions delineated thus far consist of single-base-pair substitutions resulting in nonsense, missense, or splice-site mutations. In this study, we examined four multiplex families with PXE inherited in an autosomal recessive pattern. In each family, the proband was a compound heterozygote for a single-base-pair-substitution mutation and a novel, approximately 16.5-kb deletion mutation spanning the site of the single-base-pair substitution in trans. The deletion mutation was shown to extend from intron 22 to intron 29, resulting in out-of-frame deletion of 1,213 nucleotides from the corresponding mRNA and causing elimination of 505 amino acids from the MRP6 polypeptide. The deletion breakpoints were precisely the same in all four families, which were of different ethnic backgrounds, and haplotype analysis by 13 microsatellite markers suggested that the deletion had occurred independently. Deletion breakpoints within introns 22 and 29 were embedded within AluSx repeat sequences, specifically in a 16-bp segment of DNA, suggesting Alu-mediated homologous recombination as a mechanism.

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214 Proc Natl Acad Sci USA 90:10325-10329 Germain DP, Perdu J, Remones V, Jeunemaitre X (2000) Homozygosity for the R1268Q mutation in MRP6, the pseudoxanthoma elasticum gene, is not disease-causing. Login to comment

[hide] Pseudoxanthoma elasticum: evidence for the existen... J Med Genet. 2001 Jul;38(7):457-61. Germain DP
Pseudoxanthoma elasticum: evidence for the existence of a pseudogene highly homologous to the ABCC6 gene.
J Med Genet. 2001 Jul;38(7):457-61., [PMID:11474653]

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75 Nat Genet 2000;25:228-31. 4 Germain DP, Perdu J, Remones V, Jeunemaitre X. Homozygosity for the R1268Q mutation in MRP6, the pseudoxanthoma elasticum gene, is not disease-causing. Login to comment

[hide] A spectrum of ABCC6 mutations is responsible for p... Am J Hum Genet. 2001 Oct;69(4):749-64. Epub 2001 Aug 31. Le Saux O, Beck K, Sachsinger C, Silvestri C, Treiber C, Goring HH, Johnson EW, De Paepe A, Pope FM, Pasquali-Ronchetti I, Bercovitch L, Marais AS, Viljoen DL, Terry SF, Boyd CD
A spectrum of ABCC6 mutations is responsible for pseudoxanthoma elasticum.
Am J Hum Genet. 2001 Oct;69(4):749-64. Epub 2001 Aug 31., [PMID:11536079]

Abstract [show]
To better understand the pathogenetics of pseudoxanthoma elasticum (PXE), we performed a mutational analysis of ATP-binding cassette subfamily C member 6 (ABCC6) in 122 unrelated patients with PXE, the largest cohort of patients yet studied. Thirty-six mutations were characterized, and, among these, 28 were novel variants (for a total of 43 PXE mutations known to date). Twenty-one alleles were missense variants, six were small insertions or deletions, five were nonsense, two were alleles likely to result in aberrant mRNA splicing, and two were large deletions involving ABCC6. Although most mutations appeared to be unique variants, two disease-causing alleles occurred frequently in apparently unrelated individuals. R1141X was found in our patient cohort at a frequency of 18.8% and was preponderant in European patients. ABCC6del23-29 occurred at a frequency of 12.9% and was prevalent in patients from the United States. These results suggested that R1141X and ABCC6del23-29 might have been derived regionally from founder alleles. Putative disease-causing mutations were identified in approximately 64% of the 244 chromosomes studied, and 85.2% of the 122 patients were found to have at least one disease-causing allele. Our results suggest that a fraction of the undetected mutant alleles could be either genomic rearrangements or mutations occurring in noncoding regions of the ABCC6 gene. The distribution pattern of ABCC6 mutations revealed a cluster of disease-causing variants within exons encoding a large C-terminal cytoplasmic loop and in the C-terminal nucleotide-binding domain (NBD2). We discuss the potential structural and functional significance of this mutation pattern within the context of the complex relationship between the PXE phenotype and the function of ABCC6.

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129 Premature termination mutations frequently result in the nonsense-mediated decay (NMD) of mutant mRNA products and significantly reduce mutant transcript levels (Maquat 1996; Nagy and Table 3 Missense Neutral Variants Identified in the ABCC6 Gene in a Cohort of 122 Patients CHANGE IN STATUS a ORIGIN(S)b EXON(S) NO. OF ALLELES/ PXE CHROMOSOMES NO. OF ALLELES/ CONTROL CHROMOSOMES c Amino Acid Nucleotide G61D 182GrA ht SA 2 1/244 0/200 G207R 619GrA ht Belgium 6 1/244 0/200 R265G 793ArG ht Belgium 7 1/244 0/200 K281Ed 841ArG ht, hm SA 8 5/8d Nd I319Vd 955ArG ht, hm SA 8 5/8d Nd N497K 1489CrA ht Belgium 12 1/244 0/200 V614A 1841TrC ht, hm All 14 200/244 163/200 H632Qd 1896CrA ht, hm SA, Belgium 15 17/24d Nd L953H 2858TrA ht US 22 1/244 0/200 W1241C 3723GrC ht Germany 26 1/244 0/200 R1268Q 3803GrA ht All 27 23/244 31/200 a ht p heterozygote; hm p homozygote. Login to comment
156 Most of the neutral variants were unique; however, two of these alleles (V614A and R1268Q) were found at 81.9% and 9.4%, respectively, in the cohort of patients with PXE. Login to comment
312 J Biol Chem 275:13098-13108 Germain DP, Perdu J, Remones V, Jeunemaitre X (2000) Homozygosity for the R1268Q mutation in MRP6, the pseudoxanthoma elasticum gene, is not disease-causing. Login to comment

[hide] Nucleotide binding and nucleotide hydrolysis prope... Biochemistry. 2002 Jun 25;41(25):8058-67. Cai J, Daoud R, Alqawi O, Georges E, Pelletier J, Gros P
Nucleotide binding and nucleotide hydrolysis properties of the ABC transporter MRP6 (ABCC6).
Biochemistry. 2002 Jun 25;41(25):8058-67., 2002-06-25 [PMID:12069597]

Abstract [show]
Mutations in the MRP gene family member MRP6 cause pseudoxanthoma elasticum (PXE) in humans, a disease affecting elasticity of connective tissues. The normal function of MRP6, including its physiological substrate(s), remains unknown. To address these issues, recombinant rat Mrp6 (rMrp6) was expressed in the methylotrophic yeast Pichia pastoris. The protein was expressed in the membrane fraction as a stable 170 kDa protein. Its nucleotide binding and hydrolysis properties were investigated using the photoactive ATP analogue 8-azido-[alpha-(32)P]ATP and compared to those of the drug efflux pump MRP1. rMrp6 can bind 8-azido-[alpha-(32)P]ATP in a Mg(2+)-dependent and EDTA-sensitive fashion. Co(2+), Mn(2+), and Ni(2+) can also support 8-azido-[alpha-(32)P]ATP binding by rMrp6 while Ca(2+), Cd(2+), and Zn(2+) cannot. Under hydrolysis conditions (at 37 degrees C), the phosphate analogue beryllium fluoride (BeF(x)()) can stimulate trapping of the 8-azido-[alpha-(32)P]adenosine nucleotide in rMrp6 (and in MRP1) in a divalent cation-dependent and temperature-sensitive fashion. This suggests active ATPase activity, followed by trapping and photo-cross-linking of the 8-azido-[alpha-(32)P]ADP to the protein. By contrast to MRP1, orthovanadate-stimulated nucleotide trapping in rMrp6 does not occur in the presence of Mg(2+) but can be detected with Ni(2+) ions, suggesting structural and/or functional differences between the two proteins. The rMrp6 protein can be specifically photolabeled by a fluorescent photoactive drug analogue, [(125)I]-IAARh123, with characteristics similar to those previously reported for MRP1 (1), and this photolabeling of rMrp6 can be modulated by several structurally unrelated compounds. The P. pastoris expression system has allowed demonstration of ATP binding and ATP hydrolysis by rMrp6. In addition to providing large amounts of active protein for detailed biochemical studies, this system should also prove useful to identify potential rMrp6 substrates in [(125)I]-IAARh123 photolabeling competition studies, as well as to study the molecular basis of PXE mutations, which are most often found in the NBD2 of MRP6.

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55 Interestingly, most of the single amino acid substitutions mapped in NBD2 of MRP6 (R1114P, R1138Q/ W, R1314W, W1259G, R1268Q) with none in NBD1. Login to comment

[hide] Evidence for a founder effect for pseudoxanthoma e... Hum Genet. 2002 Oct;111(4-5):331-8. Epub 2002 Sep 7. Le Saux O, Beck K, Sachsinger C, Treiber C, Goring HH, Curry K, Johnson EW, Bercovitch L, Marais AS, Terry SF, Viljoen DL, Boyd CD
Evidence for a founder effect for pseudoxanthoma elasticum in the Afrikaner population of South Africa.
Hum Genet. 2002 Oct;111(4-5):331-8. Epub 2002 Sep 7., [PMID:12384774]

Abstract [show]
Pseudoxanthoma elasticum (PXE) is a heritable elastic tissue disorder recently shown to be attributable to mutations in the ABCC6 ( MRP6) gene. Whereas PXE has been identified in all ethnic groups studied to date, the prevalence of this disease in various populations is uncertain, although often assumed to be similar. A notable exception however is the prevalence of PXE among South African Afrikaners. A previous report has suggested that a founder effect may explain the higher prevalence of PXE in Afrikaners, a European-derived population that first settled in South Africa in the 17th century. To investigate this hypothesis, we performed haplotype and mutational analysis of DNA from 24 South African families of Afrikaner, British and Indian descent. Among the 17 Afrikaner families studied, three common haplotypes and six different disease-causing variants were identified. Three of these mutant alleles were missense variants, two were nonsense mutations and one was a single base-pair insertion. The most common variant accounted for 53% of the PXE alleles, whereas other mutant alleles appeared at lower frequencies ranging from 3% to 12%. Haplotype analysis of the Afrikaner families showed that the three most frequent mutations were identical-by-descent, indicating a founder origin of PXE in this population.

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89 335 Table 3 Silent and neutral variants identified in the ABCC6 gene in a cohort of 24 South African patients with PXE (hm homozygote, ht heterozygote, aa amino acid changes, nt nucleotide changes, i- the intron in which the variant is located, No. of alleles number of variants found in the 48 PXE chromosomes analysed in this study aVariants identified by sequencing only; variants identified in either or both ABCC6 pseudogenes have not been indicated in this table aa nt Status Exon Origin No. of alleles G61D 182G→A ht 2 Afrikaner 1 T215T 645G→A ht 6 Afrikaner 2 K281Ea 841A→G ht, hm 8 Afrikaner, UK 2 T285Ta 855C→T ht, hm 8 Afrikaner, UK 2 I319Va 955A→G ht, hm 8 Afrikaner, UK 2 N411N 1233T→C ht, hm 10 Afrikaner, UK 20 V415V 1245G→A ht, hm 10 All 20 none IVS11+73G→C ht i-11 Afrikaner, UK 2 none IVS11-45C→A ht i-11 UK 1 none IVS11-41A→G ht, hm i-11 Afrikaner, UK 5 none IVS11-22C→A ht i-11 Afrikaner 1 V614A 1841T→C ht, hm 14 All 16 T630Ta 1890C→G ht, hm 15 Afrikaner, UK 11 H632Qa 1896C→A ht, hm 15 Afrikaner, UK 11 A830A 2490C→T ht, hm 19 Afrikaner, UK 6 none IVS21+30G→A ht i-21 UK 2 P945P 2835C→T ht, hm 22 Indian, UK 3 none IVS22-5delTCCC-8 ht i-22 UK 1 none IVS24-16T→C ht i-24 UK 1 none IVS24-3C→T ht i-24 AFK 1 none IVS25+55T→C ht i-25 Afrikaner, UK 8 none IVS25+90G→A ht, hm i-25 All 21 R1268Q 3803G→A ht, hm 27 Afrikaner, UK 4 none IVS27-6G→A ht i-27 Afrikaner 1 none IVS28+49C→T ht, hm i-28 Afrikaner 18 I1350L 4048A→C ht 29 UK 1 none 3` UTR+17G→A ht 3`UTR Afrikaner 2 Silent and neutral variants of ABCC6 An additional 27 variants, assumed to be neutral or silent, were identified in the course of the ABCC6 screening of our cohort of 24 South African PXE individuals (Table 3). Login to comment
92 Six other variants (G61D, K281E, I319V, V614A, H632Q and R1268Q) resulted in amino acid changes but appeared not to segregate with the disease in PXE pedigrees and were therefore likely to be neutral. Login to comment

[hide] Overexpression, purification, and functional chara... Biochim Biophys Acta. 2003 Feb 17;1610(1):63-76. Cai J, Gros P
Overexpression, purification, and functional characterization of ATP-binding cassette transporters in the yeast, Pichia pastoris.
Biochim Biophys Acta. 2003 Feb 17;1610(1):63-76., 2003-02-17 [PMID:12586381]

Abstract [show]
The ATP-binding cassette (ABC) transporter superfamily is a large gene family that has been highly conserved throughout evolution. The physiological importance of these membrane transporters is highlighted by the large variety of substrates they transport, and by the observation that mutations in many of them cause heritable diseases in human. Likewise, overexpression of certain ABC transporters, such as P-glycoprotein and members of the multidrug resistance associated protein (MRP) family, is associated with multidrug resistance in various cells and organisms. Understanding the structure and molecular mechanisms of transport of the ABC transporters in normal tissues and their possibly altered function in human diseases requires large amounts of purified and active proteins. For this, efficient expression systems are needed. The methylotrophic yeast Pichia pastoris has proven to be an efficient and inexpensive experimental model for high-level expression of many proteins, including ABC transporters. In the present review, we will summarize recent advances on the use of this system for the expression, purification, and functional characterization of P-glycoprotein and two members of the MRP subfamily.

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316 Recently, a rare MRP6 mutation (R1268Q) in a PXE patient was found to be associated with type IV hyperlipidemia and hypoalphalipoproteinemia, suggesting that MRP6 may be a determinant of plasma lipoproteins [141]. Login to comment

[hide] ABCC6/MRP6 mutations: further insight into the mol... Eur J Hum Genet. 2003 Mar;11(3):215-24. Hu X, Plomp A, Wijnholds J, Ten Brink J, van Soest S, van den Born LI, Leys A, Peek R, de Jong PT, Bergen AA
ABCC6/MRP6 mutations: further insight into the molecular pathology of pseudoxanthoma elasticum.
Eur J Hum Genet. 2003 Mar;11(3):215-24., [PMID:12673275]

Abstract [show]
Pseudoxanthoma elasticum (PXE) is a hereditary disease characterized by progressive dystrophic mineralization of the elastic fibres. PXE patients frequently present with skin lesions and visual acuity loss. Recently, we and others showed that PXE is caused by mutations in the ABCC6/MRP6 gene. However, the molecular pathology of PXE is complicated by yet unknown factors causing the variable clinical expression of the disease. In addition, the presence of ABCC6/MRP6 pseudogenes and multiple ABCC6/MRP6-associated deletions complicate interpretation of molecular genetic studies. In this study, we present the mutation spectrum of ABCC6/MRP6 in 59 PXE patients from the Netherlands. We detected 17 different mutations in 65 alleles. The majority of mutations occurred in the NBF1 (nucleotide binding fold) domain, in the eighth cytoplasmatic loop between the 15th and 16th transmembrane regions, and in NBF2 of the predicted ABCC6/MRP6 protein. The R1141X mutation was by far the most common mutation identified in 19 (32.2%) patients. The second most frequent mutation, an intragenic deletion from exon 23 to exon 29 in ABCC6/MRP6, was detected in 11 (18.6%) of the patients. Our data include 11 novel ABCC6/MRP6 mutations, as well as additional segregation data relevant to the molecular pathology of PXE in a limited number of patients and families. The consequences of our data for the molecular pathology of PXE are discussed.

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159 Table 4 Polymorphic sequence changes identified in ABCC6 Nucleotide Amino acid Location Estimated frequency (%) CA(18) F Intron4 68 V415V 1245G>A 10 33 V614A 1841T>C 14 52 T630T 1890C>G 15 22 H632Q 1896C>A 15 24 A830G 2490C>G 19 25 P945P 2846C>T 22 50 L968L 2904G>A 22 20 Int(22) F Intron22 50 R1268Q 3808G>A 27 38 The definition of disease-associated alleles essentially follows the criteria described by Le Saux et al.22 In summary, sequence variants predicted to result in nonsense or splice-site changes were considered to be disease-associated alleles if they are absent in DNA of a panel of at least 100 controls. Login to comment

[hide] Analysis of the frequent R1141X mutation in the AB... Invest Ophthalmol Vis Sci. 2003 May;44(5):1824-9. Hu X, Peek R, Plomp A, ten Brink J, Scheffer G, van Soest S, Leys A, de Jong PT, Bergen AA
Analysis of the frequent R1141X mutation in the ABCC6 gene in pseudoxanthoma elasticum.
Invest Ophthalmol Vis Sci. 2003 May;44(5):1824-9., [PMID:12714611]

Abstract [show]
PURPOSE: To characterize the ABCC6 R1141X nonsense mutation, which is implicated in more than 25% of a cohort of patients from The Netherlands with pseudoxanthoma elasticum (PXE). METHODS: A combination of single-strand conformational polymorphism (SSCP), PCR, sequencing, and Southern blot analysis was used to identify mutations in the ABCC6 gene in 62 patients. Haplotypes of 16 patients with the R1141X mutation were determined with eight polymorphic markers spanning the ABCC6 locus. The effect of the R1141X mutation on the expression of ABCC6 was studied in leukocytes and cultured dermal fibroblasts from affected skin in patients heterozygous or homozygous for the R1141X mutation. ABCC6 expression was analyzed by RT-PCR and immunocytochemistry with ABCC6-specific monoclonal antibodies. RESULTS: The ABCC6 R1141X mutation was found on 19 alleles in 16 patients with PXE and occurred in heterozygous, homozygous, or compound heterozygous form. All R1141X alleles were associated with a common haplotype, covering at least three intragenic ABCC6 markers. None of the patients or healthy control subjects had a similar ABCC6 haplotype. Furthermore, the results showed that the expression of the normal allele in R1141X heterozygotes was predominant, whereas no detectable, or very low, ABCC6 mRNA levels were found in R1141X homozygotes. Immunocytochemical staining of cultured dermal fibroblasts with ABCC6-specific monoclonal antibodies showed no evidence of the presence of a truncated protein in patients with PXE who were homozygous for R1141X. CONCLUSIONS: A specific founder effect for the R1141X mutation exists in Dutch patients with PXE. The R1141X mutation induces instability of the aberrant mRNA. Functional haploinsufficiency or loss of function of ABCC6 caused by mechanisms, such as nonsense-mediated decay (NMD), may be involved in the PXE phenotype.

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104 Three of these were used in this study to construct the following haplotypes: (1) 1896 C3A in exon 15 predicting an H632Q substitution, (2) 2490 C3G in exon 19 predicting an A830G substitution, and (3) 3803 G3A in exon 27 predicting a R1268Q substitution. Login to comment

[hide] Heterozygous carriers of Pseudoxanthoma elasticum ... J Neurol. 2003 Aug;250(8):983-6. Morcher M, Hausser I, Brandt T, Grond-Ginsbach C
Heterozygous carriers of Pseudoxanthoma elasticum were not found among patients with cervical artery dissections.
J Neurol. 2003 Aug;250(8):983-6., [PMID:12928920]

Abstract [show]
In this study of patients with spontaneous cervical artery dissections (sCAD) we searched for mutations in ABCC6, the candidate gene for Pseudoxanthoma elasticum (PXE). Genomic DNA samples from 12 sCAD patients with pronounced electron microscopic alterations in their dermal connective tissue and from 2 patients with PXE were analysed. One patient with PXE was compound heterozygous for two missense point mutations, in the second patient with PXE we did not find changes in the ABCC6 gene. We observed several missense mutations (H623Q, R3190W and R1268Q) in the patients with sCAD, but these mutations were not disease specific,since they were also detected in a series of 25 healthy control subjects.The finding of several sequence variants in sCAD patients and of disease causing mutations in one of the PXE patients suggests that our strategy of mutation search is reliable. Since we did not find disease causing mutations in our series of patients with sCAD we suggest that ABCC6 is not a candidate gene for sCAD.

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10 One patient with PXE was compound heterozygous for two missense point mutations, in the second patient with PXE we did not find changes in the ABCC6 gene.We observed several missense mutations (H623Q, R3190W and R1268Q) in the patients with sCAD, but these mutations were not disease specific, since they were also detected in a series of 25 healthy control subjects. Login to comment
35 We found three missense mutations in our patients with sCAD (H623Q, R1064W and R1268Q). Login to comment
45 However, the R1141X muTable ABCC6sequencevariationin12patientswithsCADand2patientswithPXE exon nucleotide Amino-acid Occurrence Occurrence position change among patients among controls 10 1233T¡C synonymous sCAD not tested 10 1245G¡A synonymous sCAD not tested 15 1890C¡G synonymous sCAD not tested 15 1896C¡A H623Q sCAD + 19 2490C¡T synonymous sCAD not tested 20 2631C¡A synonymous sCAD not tested 22 2835C¡T synonymous sCAD not tested 22 2836C¡A L946I PXE - 23 3190C¡T R1064W sCAD + 24 3389C¡T T1130M PXE - 27 3803G¡A R1268Q sCAD + tation is common in European patients, whereas a large deletion of exons 23-26 is repeatedly found in patients from the United States [22]. Login to comment
51 Several missense mutations (H632Q in exon 15, R1064W in exon 23 and R1268Q in exon 27) were found. Login to comment
53 A missense mutation (N411K) at this same nucleotide position was described as disease causing in a patient with PXE [13].The analysis of 25 control subjects revealed that none of the sequence variants found in the group of sCAD patients was specific, as each mutation was also detected among control subjects.Two of the missense mutations (H623Q and R1268Q) had already been found in healthy subjects [13, 18]. Login to comment

[hide] [Microvascular involvement in pseudoxanthoma elast... Presse Med. 2004 Apr 24;33(8):518-21. Perdu J, Champion K, Emmerich J, Fiessinger JN
[Microvascular involvement in pseudoxanthoma elasticum. Capillaroscopic findings].
Presse Med. 2004 Apr 24;33(8):518-21., 2004-04-24 [PMID:15235502]

Abstract [show]
OBJECTIVE: The aim of this study was to describe, for the first time, the capillary angio-architecture during pseudoxanthoma elasticum, a rare genetic disease related to mutations in the ABCC6 gene, of which the systemic calcifying involvement is responsible notably for very severe cardiovascular complications. Method Seven patients suffering from clinically and histologically documented confirmed pseudoxanthoma elasticum were examined with capillaroscopy, the absence of concomitant connective tIssue disease or diabetes having been checked beforehand. RESULTS: All the patients exhibited a microangiopathy, characterised by normal capillary density, frequent pericapillary oedema, excessively coiled fibres with a significantly increased number of minor dystrophies and, to varying degrees, a slowing down of capillary blood flow demonstrated by a sludge phenomenon. CONCLUSION: This descriptive study shows that a microangiopathy exists during pseudoxanthoma elasticum. However, the latter is not specific and a double blind controlled study is required to confirm these results. The discovery of genotype/phenotype correlations in this disease would provide a place for capillaroscopy in the diagnostic strategy in young patients or in the assessment of the cardiovascular involvement.

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61 5 Germain DP, Perdu J, Remones V, Jeunemaître X. Homozygosity for the R1268Q Mutation in MRP6, the Pseudoxanthoma Elasticum Gene, Is Not Disease-Causing. Login to comment

[hide] ABCC6 mutations in Italian families affected by ps... Hum Mutat. 2004 Nov;24(5):438-9. Gheduzzi D, Guidetti R, Anzivino C, Tarugi P, Di Leo E, Quaglino D, Ronchetti IP
ABCC6 mutations in Italian families affected by pseudoxanthoma elasticum (PXE).
Hum Mutat. 2004 Nov;24(5):438-9., [PMID:15459974]

Abstract [show]
Pseudoxanthoma elasticum (PXE) is a genetic disorder, characterized by cutaneous, ocular and cardiovascular clinical symptoms, caused by mutations in a gene (ABCC6) that encodes for MRP6 (Multidrug Resistance associated Protein 6), an ATP-binding cassette membrane transporter. The ABCC6 gene was sequenced in 38 unrelated PXE Italian families. The mutation detection rate was 82.9%. Mutant alleles occurred in homozygous, compound heterozygous and heterozygous forms, however the great majority of patients were compound heterozygotes. Twenty-three different mutations were identified, among which 11 were new. Fourteen were missense (61%); five were nonsense (22%); two were frameshift (8.5%) and two were putative splice site mutations (8.5%). The great majority of mutations were located from exon 24 to 30, exon 24 being the most affected. Among the others, exons 9 and 12 were particularly involved. Almost all mutations were located in the intracellular site of MRP6. A positive correlation was observed between patient's age and severity of the disorder, especially for eye alterations. The relevant heterogeneity in clinical manifestations between patients with identical ABCC6 mutations, even within the same family, seems to indicate that, apart from PXE causative mutations, other genes and/or metabolic pathways might influence the clinical expression of the disorder.

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134 Interestingly, it has been observed that a particular ABCC6/MRP6 polymorphism, called c.3803G>A (p.R1268Q), is associated with reduced amount of plasma triglycerides and higher plasma HDL cholesterol (Wang et al., 2001). Login to comment

[hide] New ABCC6 gene mutations in German pseudoxanthoma ... J Mol Med (Berl). 2005 Feb;83(2):140-7. Epub 2004 Nov 10. Hendig D, Schulz V, Eichgrun J, Szliska C, Gotting C, Kleesiek K
New ABCC6 gene mutations in German pseudoxanthoma elasticum patients.
J Mol Med (Berl). 2005 Feb;83(2):140-7. Epub 2004 Nov 10., [PMID:15723264]

Abstract [show]
Pseudoxanthoma elasticum (PXE; OMIM 177850 and 264800) is a rare heritable disorder of the connective tissue affecting the extracellular matrix of the skin, eyes, gastrointestinal system, and cardiovascular system. It has recently been found that mutations in the ABCC6 gene encoding the multidrug resistance-associated protein (MRP) 6 cause PXE. This study examined novel mutations in the ABCC6 gene in our cohort of 76 German PXE patients and 54 unaffected or not yet affected relatives with a view to expanding the known mutational spectrum of the gene. Mutational analysis was performed using denaturing high-performance liquid chromatography and direct sequencing. The mutational screening revealed a total of 22 different ABCC6 sequence variations. We identified seven novel and four previously described PXE-associated mutations as well as eight novel neutral ABCC6 sequence variants. The new PXE-associated mutations included five missense mutations, one single base pair deletion, and one larger out-of-frame deletion. We suspect that the novel missense mutations lead to an impaired function of MRP6. Both deletions are predicted to result in a dysfunctional MRP6 protein. The seven new ABCC6 mutations were not present in 200 alleles from healthy blood donors which served as a control cohort. Most of the PXE patients who were found to carry PXE-causing ABCC6 mutations were assumed to manifest the PXE phenotype because of a compound heterozygous genotype. However, a genotype-phenotype correlation could not be established for the detected ABCC6 mutations. In summary, our data give a further insight into the spectrum of ABCC6 mutations in PXE patients.

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181 Germain DP, Perdu J, Remones V, Jeunemaitre X (2000) Homozygosity for the R1268Q mutation in MRP6, the pseudoxanthoma elasticum gene, is not disease-causing. Login to comment
134 All but two of the PXE patients who were identified to be heterozygous carriers of the six novel mutations (p.M751K, p.R760W, p.L851P, p.S1403R, and c.2835_ 2850del16) were also found to carry one other PXE-causing ABCC6 mutation (c.2787+1G>T, p.R1141X, c.3736-1G>A, p.R1268Q). Login to comment

[hide] Identification of a DNA methylation-dependent acti... J Biol Chem. 2005 May 13;280(19):18643-50. Epub 2005 Mar 9. Aranyi T, Ratajewski M, Bardoczy V, Pulaski L, Bors A, Tordai A, Varadi A
Identification of a DNA methylation-dependent activator sequence in the pseudoxanthoma elasticum gene, ABCC6.
J Biol Chem. 2005 May 13;280(19):18643-50. Epub 2005 Mar 9., 2005-05-13 [PMID:15760889]

Abstract [show]
ABCC6 encodes MRP6, a member of the ABC protein family with an unknown physiological role. The human ABCC6 and its two pseudogenes share 99% identical DNA sequence. Loss-of-function mutations of ABCC6 are associated with the development of pseudoxanthoma elasticum (PXE), a recessive hereditary disorder affecting the elastic tissues. Various disease-causing mutations were found in the coding region; however, the mutation detection rate in the ABCC6 coding region of bona fide PXE patients is only approximately 80%. This suggests that polymorphisms or mutations in the regulatory regions may contribute to the development of the disease. Here, we report the first characterization of the ABCC6 gene promoter. Phylogenetic in silico analysis of the 5' regulatory regions revealed the presence of two evolutionarily conserved sequence elements embedded in CpG islands. The study of DNA methylation of ABCC6 and the pseudogenes identified a correlation between the methylation of the CpG island in the proximal promoter and the ABCC6 expression level in cell lines. Both activator and repressor sequences were uncovered in the proximal promoter by reporter gene assays. The most potent activator sequence was one of the conserved elements protected by DNA methylation on the endogenous gene in non-expressing cells. Finally, in vitro methylation of this sequence inhibits the transcriptional activity of the luciferase promoter constructs. Altogether these results identify a DNA methylation-dependent activator sequence in the ABCC6 promoter.

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27 In this line, the association of the R1268Q allele with variations of plasma triglyceride and the high density lipoprotein cholesterol level has been observed (19). Login to comment

[hide] Molecular genetics of pseudoxanthoma elasticum: ty... Hum Mutat. 2005 Sep;26(3):235-48. Miksch S, Lumsden A, Guenther UP, Foernzler D, Christen-Zach S, Daugherty C, Ramesar RK, Lebwohl M, Hohl D, Neldner KH, Lindpaintner K, Richards RI, Struk B
Molecular genetics of pseudoxanthoma elasticum: type and frequency of mutations in ABCC6.
Hum Mutat. 2005 Sep;26(3):235-48., [PMID:16086317]

Abstract [show]
Pseudoxanthoma elasticum (PXE) is a systemic heritable disorder that affects the elastic tissue in the skin, eye, and cardiovascular system. Mutations in the ABCC6 gene cause PXE. We performed a mutation screen in ABCC6 using haplotype analysis in conjunction with direct sequencing to achieve a mutation detection rate of 97%. This screen consisted of 170 PXE chromosomes in 81 families, and detected 59 distinct mutations (32 missense, eight nonsense, and six likely splice-site point mutations; one small insertion; and seven small and five large deletions). Forty-three of these mutations are novel variants, which increases the total number of PXE mutations to 121. While most mutations are rare, three nonsense mutations, a splice donor site mutation, and the large deletion comprising exons 23-29 (c.2996_4208del) were identified as relatively frequent PXE mutations at 26%, 5%, 3.5%, 3%, and 11%, respectively. Chromosomal haplotyping with two proximal and two distal polymorphic markers flanking ABCC6 demonstrated that most chromosomes that carry these relatively frequent PXE mutations have related haplotypes specific for these mutations, which suggests that these chromosomes originate from single founder mutations. The types of mutations found support loss-of-function as the molecular mechanism for the PXE phenotype. In 76 of the 81 families, the affected individuals were either homozygous for the same mutation or compound heterozygous for two mutations. In the remaining five families with one uncovered mutation, affected showed allelic compound heterozygosity for the cosegregating PXE haplotype. This demonstrates pseudo-dominance as the relevant inheritance mechanism, since disease transmission to the next generation always requires one mutant allelic variant from each parent. In contrast to other previous clinical and molecular claims, our results show evidence only for recessive PXE. This has profound consequences for the genetic counseling of families with PXE.

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209 Type and Frequency of Polymorphisms in ABCC6 Identi'ed in170 Chromosomes of 81 PXE FamiliesÃ Exon/ Intron Nucleotide substitution Amino acid change Location Frequency (] of families) Referencea E 03 c.232G4A p.A78T ABCC6-C2 81 This study, (C,H) IVS 03 c.345112T4C Intron duplication 81 This study IVS 03 c.345126C4T Intron 1 This study IVS 03 c.346À6G4A Intron 10 This study, (C) E 04 c.373G4A p.E125K ABCC6-C1 81 This study, (C) E 04 c.473C4T p.A158V ABCC6-C2 81 This study, (C) IVS 04 c.474113 G4A Intron duplication 2 This study IVS 04 c.474143C4T Intron duplication 80 This study, (C) IVS 04 c.475À76A4C Intron duplication 81 This study IVS 04 c.475À45C4T Intron 3 This study IVS 04 c.475À22T4C Intron duplication 80 This study, (C) E 05 c.549G4A L183L ABCC6 2 This study, (E) IVS 05 c.600123C4T Intron 1 This study E 06 c.645G4A T215T ABCC6 8 This study, (C) IVS 06 c.662112C4T Intron 1 This study, (C) E 07 c.793A4G R265G ABCC6-C1 81 This study, (C,H) IVS 07 c.794136A4C Intron duplication 81 This study, (C) E 08 c.841A4G K281E ABCC6-Cx 81 This study, (H) E 08 c.855C4T T285T ABCC6-C1 81 This study, (C) E 08 c.955A4G I319V ABCC6-Cx 81 This study, (H) E 09 c.1077A4G S359S ABCC6, ABCC6-C1 1 This study, (C,H) E 09 c.1132C4T Q378X ABCC6-C1 81 This study, (C,H) E 09 c.1141T4C L381L ABCC6, ABCC6-C1 81 This study, (C,H) IVS 09 c.117616C4T No SSM Intron 1 This study E 10 c.1233T4C N411N ABCC6 1 This study, (B,L) E 10 c.1245G4A V415V ABCC6 Frequent This study, (B,L) IVS 10 c.133817C4G Intron Frequent This study IVS 10 c.1338120C4G Intron Frequent This study IVS 10 c.1338162G4C Intron Frequent This study IVS 11 c.1432À41A4G Intron Frequent This study, (E) E 12 c.1540G4A V514I ABCC6 1 This study IVS 12 c.1635147C4T Intron Frequent This study E 14 c.1841T4C V614A ABCC6 Frequent This study, (B,E) IVS 14 c.1868À57G4A Intron 3 This study E 15 c.1890C4G T630T ABCC6 Frequent This study, (B,L) E 15 c.1896C4A H632Q ABCC6 Frequent This study, (C,G) E 17 c.2171G4A R724K ABCC6 2 This study E 17 c.2175A4T V725V ABCC6 2 This study E 17 c.2224A4G I742V ABCC6 2 This study E 19 c.2490C4T A830A ABCC6 Frequent This study, (E) E 22 c.2820T4G R940R ABCC6 1 This study E 22 c.2835C4T P945P ABCC6 8 This study, (J) E 22 c.2836C4A L946I ABCC6 3 This study E 22 c.2904G4A L968L ABCC6 1 This study, (J) E 23 c.3190C4T R1064W ABCC6 2 This study IVS 24 c.3507À16T4C No SSM Intron 4 This study IVS 24 c.3507À3C4T No SSM Intron 3 This study E 27 c.3803G4A R1268Q ABCC6 Frequent This study, (C,M) IVS 27 c.3883À24G4A Intron 1 This study IVS 28 c.4041149C4T Intron Frequent This study, (E) IVS 28 c.4042À30C4T Intron Frequent This study IVS 29 c.420819G4A Intron 2 This study E 30 c.4305C4T G1435G ABCC6 1 This study IVS 30 c.4405À31G4A Intron Frequent This study 30 UTR c.4512117G4A UTR 5 This study, (E) 30 UTR c.4512138G4A UTR 1 This study ÃDNA mutation numbering is based on the ABCC6 cDNA sequence (GenBank accession no. AF076622.1) and 11 corresponds to the A of the ATG translation initiation codon of the reference sequence. Login to comment
199 Coding sequence SNPs were considered as neutral (non-disease-causing) when they resulted in a synonymous amino acid substitution or a nonsynonymous substitution that did not cosegregate with the disease haplotype and phenotype (p.V614A, p.R724K, p.I742V, p.L946I, p.R1064W, and p.R1268Q) or did cosegregate with other PXE mutations in linkage disequilibrium in individual families (p.V514I, p.H632Q, and p.R1268Q). Login to comment

[hide] Elastosis perforans serpiginosa-like pseudoxanthom... Br J Dermatol. 2005 Aug;153(2):431-4. Meyer S, Zanardo L, Kaminski WE, Horn P, Schmitz G, Hohenleutner U, Herrmann WA, Landthaler M, Vogt T
Elastosis perforans serpiginosa-like pseudoxanthoma elasticum in a child with severe Moya Moya disease.
Br J Dermatol. 2005 Aug;153(2):431-4., [PMID:16086762]

Abstract [show]
A 2-year-old girl with Moya Moya disease who had relapsing cerebrovascular strokes presented with loose skin folds, 'chicken' skin appearance and perforating elastosis serpiginosa-like lesions in the genitocrural region. Histologically, calcified material perforating the epidermis and adjacent short curled and mineralized elastic fibres suggested a variant of pseudoxanthoma elasticum (PXE). As PXE is known to be caused by various mutations in the transmembrane transporter ABCC6 gene, we hypothesized that a novel ABCC6 mutation may underlie this unique combination of PXE and elastopathic vascular damage. Therefore, the complete ABCC6 coding region of the patient and her parents was screened for genetic alterations. No bona fide disease-causing mutation of ABCC6 could be found in the child and in her parents. However, two novel allelic amino acid substitutions (Arg1273Lys and Glu1293Lys; exon 27) were found in the girl and her father, localized in close proximity to the region that codes for the functionally critical second nucleotide-binding fold of ABCC6. Although a causal involvement of these amino acid substitutions could not be proven based on this study, both heterozygote substitutions may possibly have interacted with other undetected recessive maternal ABCC6 changes in the child. To the best of our knowledge, this is the first report of an association between early-onset PXE and severe Moya Moya syndrome possibly related to ABCC6 changes.

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51 These comprise three adjacent amino acid substitutions in exon 27 (Arg1268Gln, Arg1273Lys and Glu1293Lys) and a single Arg1418Gln exchange in exon 30 (Fig. Login to comment
53 The Arg1268Gln substitution, which results from a G fi A nucleotide exchange in position 3803, was found in both the index patient and her healthy father. This substitution has previously been suggested to be causatively linked to PXE,9 but was later recognized as a common polymorphism with significant allelic frequency.10 In contrast, the Arg1273Lys and Glu1293Lys substitutions in exon 27 are new and have not previously been reported. Login to comment

[hide] Acute myocardial infarction and a new ABCC6 mutati... Int J Cardiol. 2007 Mar 20;116(2):261-2. Epub 2006 Jul 18. Kiec-Wilk B, Surdacki A, Dembinska-Kiec A, Michalowska J, Stachura-Deren M, Dubiel JS, Dudek D, Rakowski T, Szastak G, Bodzioch M, Aslanidis C, Schmitz G
Acute myocardial infarction and a new ABCC6 mutation in a 16-year-old boy with pseudoxanthoma elasticum.
Int J Cardiol. 2007 Mar 20;116(2):261-2. Epub 2006 Jul 18., 2007-03-20 [PMID:16854481]

Abstract [show]
Pseudoxanthoma elasticum is caused by mutations of the ABCC6 gene. We hereby report a case of pseudoxanthoma elasticum with clinical features dominated by early coronary involvement in addition to typical skin and ocular abnormalities. A 16-year-old survivor of acute myocardial infarction with 3-vessel coronary artery disease exhibited compound heterozygosity for the well-known nonsense mutation (c.3421C>T; R1141X) in exon 24 and a novel missense mutation (c.3662G>A; R1221H) in exon 26 of the ABCC6 gene.

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24 The patient was also a heterozygous carrier of a neutral polymorphism (c.3803G>A; R1268Q) in exon 27 [2] (Fig. 3). Login to comment

[hide] Gene expression profiling of ABC transporters in d... Lab Invest. 2008 Dec;88(12):1303-15. Epub 2008 Oct 20. Hendig D, Langmann T, Kocken S, Zarbock R, Szliska C, Schmitz G, Kleesiek K, Gotting C
Gene expression profiling of ABC transporters in dermal fibroblasts of pseudoxanthoma elasticum patients identifies new candidates involved in PXE pathogenesis.
Lab Invest. 2008 Dec;88(12):1303-15. Epub 2008 Oct 20., [PMID:18936737]

Abstract [show]
Mutations in the ABCC6 gene, encoding the multidrug resistance-associated protein 6 (MRP6), cause pseudoxanthoma elasticum (PXE). This heritable disorder leads to pathological alterations in connective tissues. The implication of MRP6 deficiency in PXE is still unknown. Moreover, nothing is known about a possible compensatory expression of other ATP binding-cassette (ABC) transporter proteins in MRP6-deficient cells. We investigated the gene expression profile of 47 ABC transporters in human dermal fibroblasts of healthy controls (n=2) and PXE patients (n=4) by TaqMan low-density array. The analysis revealed the expression of 37 ABC transporter genes in dermal fibroblasts. ABCC6 gene expression was not quantifiable in fibroblasts derived from PXE patients. Seven genes (ABCA6, ABCA9, ABCA10, ABCB5, ABCC2, ABCC9 and ABCD2) were induced, whereas the gene expression of one gene (ABCA3) was decreased, comparing controls and PXE patients (with at least twofold changes). We reanalyzed the gene expression of selected ABC transporters in a larger set of dermal fibroblasts from controls and PXE patients (n=6, each). Reanalysis showed high interindividual variability between samples, but confirmed the results obtained in the array analysis. The gene expression of ABC transporter genes, as well as lineage markers of PXE, was further examined after inhibition of ABCC6 gene expression by using specific small-interfering RNA. These experiments corroborated the observed gene expression alterations, most notably in the ABCA subclass (up to fourfold, P<0.05). We therefore conclude that MRP6-deficient dermal fibroblasts exhibit a distinct gene expression profile of ABCA transporters, potentially to compensate for MRP6 deficiency. Moreover, our results point to a function for ABCC6/MRP6 in sterol transport, as sterols are preferential regulators of ABCA transporter activity and expression. Further studies are now required to uncover the role of ABCA transporters in PXE.

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173 It is mainly involved in HDL biosynthesis and cholesterol efflux.39,40 Polymorphisms in the ABCA1 were associated with cardiovascular disease and low plasma HDL levels.41-43 Wang et al previously reported that plasma HDL concentrations varied in a PXE patient and carriers of the ABCC6/MRP6 polymorphisms p.R1268Q.44 Furthermore, abcc6 knockout mice developed a 25% reduction in plasma HDL cholesterol.8 ABCA3 is a regulator of lamellar body metabolism and was reported to form lipid containing vesicles in human embryonic kidney cells.45 Little is known about the physiological function of the ABCA6-like transporters including ABCA6, ABCA9, ABCA10. Login to comment

[hide] Mutation analysis (ABCC6) in a family with pseudox... Br J Dermatol. 2010 Sep;163(3):641-3. doi: 10.1111/j.1365-2133.2010.09856.x. Epub 2010 May 11. Li Q, Torok L, Kocsis L, Uitto J
Mutation analysis (ABCC6) in a family with pseudoxanthoma elasticum: presymptomatic testing with prognostic implications.
Br J Dermatol. 2010 Sep;163(3):641-3. doi: 10.1111/j.1365-2133.2010.09856.x. Epub 2010 May 11., [PMID:20491760]

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51 7 Germain DP, Perdu J, Remones V, Jeunemaitre X. Homozygosity for the R1268Q mutation in MRP6, the pseudoxanthoma elasticum gene, is not disease-causing. Login to comment
17 The analysis of the ABCC6 gene was performed by polymerase chain reaction amplification of all exons and flanking intronic sequences, followed by automated nucleotide sequencing, as described previously.2 Two homozygous sequence variants were identified in the ABCC6 gene of the proband: p.R1221H and p.R1268Q. Login to comment
22 In contrast, the p.R1268Q sequence variant has been suggested to be a relatively common polymorphism with an allelic frequency of ~30% in healthy Caucasian and Japanese populations.7,8 Collectively, it appears that p.R1221H is the pathogenic mutation resulting in PXE, when present in both alleles, as in the case of the proband of this study. Login to comment
34 The mutation p.R1221H cosegregates in the family with an allelic polymorphism, p.R1268Q (a). Login to comment

[hide] Mutational analysis of the ABCC6 gene and the prox... Hum Mutat. 2006 Aug;27(8):831. Schulz V, Hendig D, Henjakovic M, Szliska C, Kleesiek K, Gotting C
Mutational analysis of the ABCC6 gene and the proximal ABCC6 gene promoter in German patients with pseudoxanthoma elasticum (PXE).
Hum Mutat. 2006 Aug;27(8):831., [PMID:16835894]

Abstract [show]
Pseudoxanthoma elasticum (PXE) is a genetic disorder characterized by calcification of elastic fibers in dermal, ocular, and cardiovascular tissues. Recently, ABCC6 mutations were identified as causing PXE. In this follow-up study we report the investigation of 61 German PXE patients from 53 families, hitherto the largest cohort of German PXE patients screened for the complete ABCC6 gene. In addition, we characterized the proximal ABCC6 promoter of PXE patients according to mutation. In this study we identified 32 disease-causing ABCC6 variants, which had been described previously by us and others, and 10 novel mutations (eight missense mutations and two splice site alterations). The mutation detection rate among index patients was 87.7%. Frequent alterations were the PXE-mutations p.R1141X, Ex23,_Ex29del, and c.2787+1G > T. In the ABCC6 promoter we found the polymorphisms c.-127C > T, c.-132C > T, and c.-219A > C. The difference in the c.-219A > C frequencies between PXE patients and controls were determined as statistically significant. Interestingly, c.-219A > C is located in a transcriptional activator sequence of the ABCC6 promoter and occurred in a binding site for a transcriptional repressor, predominantly found in genes that participate in lipid metabolism. Obtaining these genetic data signifies our contribution to elucidating the pathogenetics of PXE.

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183 This assumption is confirmed by the fact that an association of the polymorphism p.R1268Q in the exon 27 of the ABCC6 gene with plasma lipoprotein levels has already been observed (Wang et al., 2001). Login to comment

[hide] Novel mutations of ABCC6 gene in Japanese patients... Biochem Biophys Res Commun. 2009 Mar 13;380(3):548-53. Epub 2009 Jan 25. Sato N, Nakayama T, Mizutani Y, Yuzawa M
Novel mutations of ABCC6 gene in Japanese patients with Angioid streaks.
Biochem Biophys Res Commun. 2009 Mar 13;380(3):548-53. Epub 2009 Jan 25., 2009-03-13 [PMID:19284998]

Abstract [show]
Angioid streaks (AS) are eye abnormalities caused by breaks in Bruch's membrane. The condition is often associated with pseudoxanthoma elasticum (PXE). The ATP-binding cassette, sub-family C (CFTR/MRP), member 6 (ABCC6) is reported to be the causal gene for PXE, although there have been no reports on whether the ABCC6 gene is the causal gene for AS. The aims of this study are to isolate the causal mutations for AS using a haplotype-based case-control study. We genotyped 54 Japanese AS patients and 150 controls for 5 single-nucleotide polymorphisms (SNPs). A simple association study using each SNP and a haplotype-based case-control study were performed. Twelve patients with special haplotypes for AS were selected, and were then subjected to gene sequencing. Six variants were successfully identified as causal mutations for AS (p.R419Q, p.E422K, c.2542delG, Del_Exon23, c.3774-3775insC and p.E1427K), and 4 of these were novel. This method can be applied to both identifying susceptibility variants of multifactorial diseases and isolating mutations in single-gene diseases.

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84 We identified 8 nonsynonymous variants and a deletion variant in the exon regions; p.R419Q (Exon10), p.S587C (exon13), p.V614A (Exon14), p.H632Q (Exon15), c.2542delG (Exon19), p.A950V (Exon22), p.R1268Q (Exon27) and p.E1427K (Exon30). Login to comment
104 Disease-causing mutations The homozygous p.R419Q and the homozygous p.R1268Q were found in 2 subjects with the homozygous GTGG/GTGG diplotype. The homozygous c.2542delG and the homozygous p.H632Q or homozygous p.V614A were found in each subject with the homozygous ATGA/ATGA diplotype. The homozygous Del_Exon23 was found in 2 subjects with the homozygous GTGA/GTGA diplotype. Login to comment
106 The heterozygous p.E1427K and p.V614A or p.H632Q or p.R1268Q were found in a subject with the heterozygous GTAA/ATGG diplotype. The heterozygous c.2542delG and p.V614A or p.H632Q were found in a subject with the heterozygous GTAA/ACAA diplotype. The heterozygous p.S587C was found in a subject with the heterozygous GTGA/GCGA diplotype, and the heterozygous p.A950V was found in a subject with the heterozygous GTAA/GCAA diplotype. Login to comment
109 Consequently, p.S587C (exon13), p.V614A (Exon14), p.H632Q (Exon15), p.A950V (Exon22) and p.R1268Q (Exon27) were excluded from among the disease-causing mutations because they were seen in the control group. Login to comment
110 Of the 9 variants, p.V614A, p.H632Q and p.R1268Q were previously reported as non-causal variants for PXE. Although c.2542delG (Exon19) was seen in the control group, this is defined as the disease-causing mutation because it yields a premature stop codon. Login to comment
157 Exon Mutation AS Control Decision Wild/Wild Wild/Mut Mut/Mut Wild/Wild Wild/Mut Mut/Mut Undetermine 10 c.1256G>A (p.R419Q) 45 3 6 150 0 0 0 * 10 c.1264G>A (p.E422K) 53 1 0 150 0 0 0 * 10 c.1283A>G (p.N428S) 54 0 0 148 2 0 0 # 10 c.1312G>A (p.V438M) 54 0 0 149 1 0 0 # 13 c.1760C>G (p.S587C) 53 1 0 149 1 0 0 # 14 c.1841T>C (p.V614A) 40 12 2 89 56 5 0 $ 15 c.1896C>A (p.H632Q) 30 15 9 90 55 5 0 $ 19 c.2542delG 34 13 7 149 1 0 0 * 22 c.2849C>T (p.A950V) 53 1 0 149 1 0 0 # 23 Del_Exon23 52 0 2 150 0 0 0 * 27 c.3803G>A (p.R1268Q) 29 16 9 105 42 3 0 $ 27 c.3774-3775insertC 53 1 0 147 0 0 3 * 30 c.4279G>A (p.E1427K) 53 1 0 150 0 0 0 * For ABCC6 proteins, the designations for the mutations refer to the position of the amino acid substitution, where amino acid terminus. Nonsynonymous variants were shown by the amino acid numbers started by the strat codon methionine. The cDNA base numbers refer to the nucleotide in the cDNA, where nucleotide 1 is the A of the first ATG. * Causal mutation definitely. Login to comment

[hide] Pseudoxanthoma elasticum: progress in diagnostics ... Am J Med Genet A. 2011 Jul;155A(7):1517-26. doi: 10.1002/ajmg.a.34067. Epub 2011 Jun 10. Uitto J, Bercovitch L, Terry SF, Terry PF
Pseudoxanthoma elasticum: progress in diagnostics and research towards treatment : Summary of the 2010 PXE International Research Meeting.
Am J Med Genet A. 2011 Jul;155A(7):1517-26. doi: 10.1002/ajmg.a.34067. Epub 2011 Jun 10., [PMID:21671388]

Abstract [show]
Pseudoxanthoma elasticum (PXE), a prototypic heritable disorder with ectopic mineralization, manifests with characteristic skin findings, ocular involvement, and cardiovascular problems. The classic forms of PXE are due to loss-of-function mutations in the ABCC6 gene, which encodes ABCC6, a putative transmembrane efflux transporter expressed primarily in the liver. While considerable progress has recently been made in understanding the molecular genetics and pathomechanisms of PXE, no effective or specific treatment is currently available for this disorder. PXE International, the premiere patient advocacy organization, organized a workshop in November 2010 to assess the current state of diagnostics and research to develop an agenda towards treatment of PXE. This overview summarizes the progress in PXE research, with emphasis on molecular therapies for this, currently intractable, disorder.

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25 There are recent suggestions, however, that certain mutations in ABCC6 may bestatistically associatedwithinvolvementofspecifictargetorgans, such as the p.R1268Q mutation being associated with early onset of angioidstreaks[Satoetal.,2009;Lietal.,2011a],andthestopcodon mutation p.R1141X possibly predisposing the individuals to car- diovascularinvolvementindependentofhyperlipidemiainpatients with PXE [K€obl€os et al., 2010; Pisciotta et al., 2010]. Login to comment

[hide] Xenobiotic, bile acid, and cholesterol transporter... Pharmacol Rev. 2010 Mar;62(1):1-96. Epub 2010 Jan 26. Klaassen CD, Aleksunes LM
Xenobiotic, bile acid, and cholesterol transporters: function and regulation.
Pharmacol Rev. 2010 Mar;62(1):1-96. Epub 2010 Jan 26., [PMID:20103563]

Abstract [show]
Transporters influence the disposition of chemicals within the body by participating in absorption, distribution, and elimination. Transporters of the solute carrier family (SLC) comprise a variety of proteins, including organic cation transporters (OCT) 1 to 3, organic cation/carnitine transporters (OCTN) 1 to 3, organic anion transporters (OAT) 1 to 7, various organic anion transporting polypeptide isoforms, sodium taurocholate cotransporting polypeptide, apical sodium-dependent bile acid transporter, peptide transporters (PEPT) 1 and 2, concentrative nucleoside transporters (CNT) 1 to 3, equilibrative nucleoside transporter (ENT) 1 to 3, and multidrug and toxin extrusion transporters (MATE) 1 and 2, which mediate the uptake (except MATEs) of organic anions and cations as well as peptides and nucleosides. Efflux transporters of the ATP-binding cassette superfamily, such as ATP-binding cassette transporter A1 (ABCA1), multidrug resistance proteins (MDR) 1 and 2, bile salt export pump, multidrug resistance-associated proteins (MRP) 1 to 9, breast cancer resistance protein, and ATP-binding cassette subfamily G members 5 and 8, are responsible for the unidirectional export of endogenous and exogenous substances. Other efflux transporters [ATPase copper-transporting beta polypeptide (ATP7B) and ATPase class I type 8B member 1 (ATP8B1) as well as organic solute transporters (OST) alpha and beta] also play major roles in the transport of some endogenous chemicals across biological membranes. This review article provides a comprehensive overview of these transporters (both rodent and human) with regard to tissue distribution, subcellular localization, and substrate preferences. Because uptake and efflux transporters are expressed in multiple cell types, the roles of transporters in a variety of tissues, including the liver, kidneys, intestine, brain, heart, placenta, mammary glands, immune cells, and testes are discussed. Attention is also placed upon a variety of regulatory factors that influence transporter expression and function, including transcriptional activation and post-translational modifications as well as subcellular trafficking. Sex differences, ontogeny, and pharmacological and toxicological regulation of transporters are also addressed. Transporters are important transmembrane proteins that mediate the cellular entry and exit of a wide range of substrates throughout the body and thereby play important roles in human physiology, pharmacology, pathology, and toxicology.

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7172 These findings are consistent with the R1268Q variant of ABCC6 in pseudoxanthoma elasticum patients that is associated with type IV hyperlipoproteinemia with hypoalphalipoproteinemia (Wang et al., 2001a). Login to comment
7169 These findings are consistent with the R1268Q variant of ABCC6 in pseudoxanthoma elasticum patients that is associated with type IV hyperlipoproteinemia with hypoalphalipoproteinemia (Wang et al., 2001a). Login to comment

[hide] Functional hot spots in human ATP-binding cassette... Protein Sci. 2010 Nov;19(11):2110-21. Kelly L, Fukushima H, Karchin R, Gow JM, Chinn LW, Pieper U, Segal MR, Kroetz DL, Sali A
Functional hot spots in human ATP-binding cassette transporter nucleotide binding domains.
Protein Sci. 2010 Nov;19(11):2110-21., [PMID:20799350]

Abstract [show]
The human ATP-binding cassette (ABC) transporter superfamily consists of 48 integral membrane proteins that couple the action of ATP binding and hydrolysis to the transport of diverse substrates across cellular membranes. Defects in 18 transporters have been implicated in human disease. In hundreds of cases, disease phenotypes and defects in function can be traced to nonsynonymous single nucleotide polymorphisms (nsSNPs). The functional impact of the majority of ABC transporter nsSNPs has yet to be experimentally characterized. Here, we combine experimental mutational studies with sequence and structural analysis to describe the impact of nsSNPs in human ABC transporters. First, the disease associations of 39 nsSNPs in 10 transporters were rationalized by identifying two conserved loops and a small alpha-helical region that may be involved in interdomain communication necessary for transport of substrates. Second, an approach to discriminate between disease-associated and neutral nsSNPs was developed and tailored to this superfamily. Finally, the functional impact of 40 unannotated nsSNPs in seven ABC transporters identified in 247 ethnically diverse individuals studied by the Pharmacogenetics of Membrane Transporters consortium was predicted. Three predictions were experimentally tested using human embryonic kidney epithelial (HEK) 293 cells stably transfected with the reference multidrug resistance transporter 4 and its variants to examine functional differences in transport of the antiviral drug, tenofovir. The experimental results confirmed two predictions. Our analysis provides a structural and evolutionary framework for rationalizing and predicting the functional effects of nsSNPs in this clinically important membrane transporter superfamily.

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72 Predictions of the Functional Effects of 40 nsSNPs in ABC Transporters Comon name HUGO name Mutation NBD Prediction BSEP ABCB11 E592Q NBD1 Neutral BSEP ABCB11 N591S NBD1 Neutral BSEP ABCB11 Q558H NBD1 Neutral BSEP ABCB11 V444A NBD1 Neutral BSEP ABCB11 E1186K NBD2 Disease MDR1 ABCB1 P1051A NBD2 Neutral MDR1 ABCB1 S1141T NBD2 Neutral MDR1 ABCB1 T1256K NBD2 Disease MDR1 ABCB1 V1251I NBD2 Neutral MDR1 ABCB1 W1108R NBD2 Disease MRP2 ABCC2 I670T NBD1 Disease MRP2 ABCC2 L849R NBD1 Disease MRP2 ABCC2 C1515Y NBD2 Disease MRP3 ABCC3 D770N NBD1 Neutral MRP3 ABCC3 K718M NBD1 Neutral MRP3 ABCC3 T809M NBD1 Disease MRP3 ABCC3 V765L NBD1 Disease MRP3 ABCC3 Q1365R NBD2 Disease MRP3 ABCC3 R1297H NBD2 Disease MRP3 ABCC3 R1348C NBD2 Disease MRP3 ABCC3 R1381S NBD2 Disease MRP4 ABCC4 G487E NBD1 Disease MRP4 ABCC4 K498E NBD1 Neutral MRP4 ABCC4 R1220Q NBD2 Neutral MRP4 ABCC4 T1142M NBD2 Neutral MRP4 ABCC4 V1071I NBD2 Neutral MRP6 ABCC6 I1330L NBD1 Neutral MRP6 ABCC6 I742V NBD1 Neutral MRP6 ABCC6 P664S NBD1 Neutral MRP6 ABCC6 R724K NBD1 Neutral MRP6 ABCC6 R769K NBD1 Neutral MRP6 ABCC6 A1291T NBD2 Neutral MRP6 ABCC6 E1369K NBD2 Neutral MRP6 ABCC6 G1327E NBD2 Disease MRP6 ABCC6 L1416R NBD2 Disease MRP6 ABCC6 R1268Q NBD2 Disease MRP6 ABCC6 R1461H NBD2 Disease MXR ABCG2 I206L NBD1 Neutral MXR ABCG2 P269S NBD1 Disease MXR ABCG2 Q141K NBD1 Neutral nsSNPs. Login to comment

[hide] The vascular phenotype in Pseudoxanthoma elasticum... Front Genet. 2013 Feb 12;4:4. doi: 10.3389/fgene.2013.00004. eCollection 2013. Leftheriotis G, Omarjee L, Le Saux O, Henrion D, Abraham P, Prunier F, Willoteaux S, Martin L
The vascular phenotype in Pseudoxanthoma elasticum and related disorders: contribution of a genetic disease to the understanding of vascular calcification.
Front Genet. 2013 Feb 12;4:4. doi: 10.3389/fgene.2013.00004. eCollection 2013., [PMID:23408347]

Abstract [show]
Vascular calcification is a complex and dynamic process occurring in various physiological conditions such as aging and exercise or in acquired metabolic disorders like diabetes or chronic renal insufficiency. Arterial calcifications are also observed in several genetic diseases revealing the important role of unbalanced or defective anti- or pro-calcifying factors. Pseudoxanthoma elasticum (PXE) is an inherited disease (OMIM 264800) characterized by elastic fiber fragmentation and calcification in various soft conjunctive tissues including the skin, eyes, and arterial media. The PXE disease results from mutations in the ABCC6 gene, encoding an ATP-binding cassette transporter primarily expressed in the liver, kidneys suggesting that it is a prototypic metabolic soft-tissue calcifying disease of genetic origin. The clinical expression of the PXE arterial disease is characterized by an increased risk for coronary (myocardial infarction), cerebral (aneurysm and stroke), and lower limb peripheral artery disease. However, the structural and functional changes in the arterial wall induced by PXE are still unexplained. The use of a recombinant mouse model inactivated for the Abcc6 gene is an important tool for the understanding of the PXE pathophysiology although the vascular impact in this model remains limited to date. Overlapping of the PXE phenotype with other inherited calcifying diseases could bring important informations to our comprehension of the PXE disease.

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109 Althoughseveralmissense mutations (H623Q, R3190W, and R1268Q) were found in the patients with carotid dissection, these mutations were not disease-causing as they were also detected in healthy subjects (Morcher et al., 2003). Login to comment

[hide] ABCC6 Mutation in Patients with Angioid Streaks. Int J Biomed Sci. 2006 Feb;2(1):7-12. Mizutani Y, Nakayama T, Asai S, Shimada H, Yuzawa M
ABCC6 Mutation in Patients with Angioid Streaks.
Int J Biomed Sci. 2006 Feb;2(1):7-12., [PMID:23674961]

Abstract [show]
Angioid streaks (AS) are hereditary eye conditions caused by breaks in the elastic layer of Bruch's membrane. Patients with AS are also frequently affected with pseudoxanthoma elasticum (PXE). The locus of PXE has been reported to exist in chromosome 16p13.1, and the ABCC6 gene in this locus has been identified as the causal gene of PXE. In this study we investigated the association of the ABCC6 gene and AS. Elucidation of the causal gene of AS will be useful for gene diagnosis in the future. Many mutations in patients with PXE are found in exons 24 and 27 of the ABCC6 gene in previous reports. Therefore, we examined exons 24 and 27 of the ABCC6 gene using the single-strand conformation polymorphism technique. There was no mutation or polymorphism in exon 24. The base substitution of G3803A was identified in exon 27, with a change in the amino acid from CGG to CAG (R1268Q). The genotype frequencies in patients with AS were G/G 52% (23/44), G/A 32% (14/44) and A/A 16% (14/44). In control subjects, the genotype frequencies were G/G 69% (107/154), G/A 29% (44/154) and A/A 2% (3/154). Highly significant differences were observed in both genotype and allele frequencies of R1268Q between patients with AS and control subjects (p<0.001, p<0.002; chi-square test). In conclusion, the missense mutation R1268Q in the ABCC6 gene is not a specific marker of PXE, but is associated with the disease state of AS.

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8 The base substitution of G3803A was identified in exon 27, with a change in the amino acid from CGG to CAG (R1268Q). Login to comment
11 Highly significant differences were observed in both genotype and allele frequencies of R1268Q between patients with AS and control subjects (p<0.001, p<0.002; chi-square test). Login to comment
12 In conclusion, the missense mutation R1268Q in the ABCC6 gene is not a specific marker of PXE, but is associated with the disease state of AS. Login to comment
72 This substitution yields an amino acid change from CGG (Arg) to CAG (Gln) (R1268Q) (Fig. 2). Login to comment
73 We investigated the frequencies of the G3803A (R1268Q) genotypes by the RFLP method (Fig. 3). Login to comment
77 Arrow indicates the nucleotide constitution with a change in the amino acid (R1268Q). Login to comment
104 This nucleotide substitution results in a substitution of the amino acid arginine (CGG) to glutamine (CAG) (R1268Q). Login to comment
105 The association of R1268Q with PXE has been reported, but opinions regarding this relationship remain controversial. Login to comment
106 Ringpfeil et al (10) reported that R1268Q was not found in control subjects, and concluded that it represented a mutation and not a polymorphism in patients with PXE. Login to comment
108 On the other hand, other studies have reported that R1268Q was a polymorphism, and not a mutation (20, 21). Login to comment
110 Germain et al (22) determined the frequency of R1268Q in 62 healthy Caucasian volunteers, and reported the genotype frequencies in their control subjects as G/G 66%, G/A 29% and A/A 5%. Login to comment
111 They detected no differences in genotype frequency between the control subjects and patients with PXE, and concluded that R1268Q was a harmless polymorphism. Login to comment
112 The genotype frequency of R1268Q in Caucasians is very similar to that in healthy Japanese in the present study (Table 2). Login to comment
113 There was no significant difference in genotype frequency between our Japanese controls and the reported Caucasian volunteers (p=0.50), suggesting that there is no racial difference in the frequency of R1268Q. Login to comment
121 In the present study, we found significant differences both in genotype frequency and allele frequency of R1268Q between patients with AS and the controls. Login to comment
123 These results suggest that R1268Q may represent a genetic marker for AS rather than PXE. Login to comment
124 Germain et al (22) described R1268Q as a nonfunctional substitution in case control studies of patients with PXE. Login to comment
125 However, R1268Q seems to have etiological significance in patients with AS in the present study. Login to comment
126 Therefore, detection of R1268Q warrants not only examination for the skin disease PXE, but also investigations of other systemic symptoms including AS and cardiovascular system involvement. Login to comment
137 A single nucleotide substitution was found in exon 27, which resulted in the substitution of an amino acid (R1268Q). Login to comment
138 Significant differences in genotype and allele frequencies of R1268Q were observed between patients with AS and control subjects. Login to comment
139 However, no significant difference in allele frequency of R1268Q was found between patients with AS with and without PXE. Login to comment
140 These findings indicate that R1268Q is not a specific marker of PXE, but is a missense mutation associated with the disease state of AS. Login to comment

[hide] New insights into the pathogenesis of pseudoxantho... Front Genet. 2013 Jun 19;4:114. doi: 10.3389/fgene.2013.00114. eCollection 2013. Hendig D, Knabbe C, Gotting C
New insights into the pathogenesis of pseudoxanthoma elasticum and related soft tissue calcification disorders by identifying genetic interactions and modifiers.
Front Genet. 2013 Jun 19;4:114. doi: 10.3389/fgene.2013.00114. eCollection 2013., [PMID:23802012]

Abstract [show]
Screening of the adenosine triphosphate binding cassette transporter protein subfamily C member 6 gene (ABCC6) in pseudoxanthoma elasticum (PXE) revealed a mutation detection rate of approximately 87%. Although 25% of the unidentified disease alleles underlie deletions/insertions, there remain several PXE patients with no clear genotype. The recent identification of PXE-related diseases and the high intra-familiar and inter-individual clinical variability of PXE led to the assumption that secondary genetic co-factors exist. Here, we summarize current knowledge of the genetics underlying PXE and PXE-related disorders based on human and animal studies. Furthermore, we discuss the role of genetic interactions and modifier genes in PXE and PXE-related diseases characterized by soft tissue calcification.

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115 Wang et al. (2001) reported an association of the frequent ABCC6 p.R1268Q variant (c.3803G>A, rs2238472) with plasma triglyceride and low HDL (high-density lipoprotein) cholesterol. Login to comment