ABCMdb

PMID: 15287992

Claustres M, Altieri JP, Guittard C, Templin C, Chevalier-Porst F, Des Georges M
Are p.I148T, p.R74W and p.D1270N cystic fibrosis causing mutations?
BMC Med Genet. 2004 Aug 2;5:19., 2004-08-02 [PubMed]

Sentences

No. Mutations Sentence Comment

1 ABCC7 p.Asp1270Asn ABCC7 p.Arg74Trp ABCC7 p.Ile148Thr Mireille Claustres*1, Jean-Pierre Altiéri1, Caroline Guittard1, Carine Templin1, Françoise Chevalier-Porst2 and Marie Des Georges1 Address: 1Laboratoire de Génétique Moléculaire, Institut Universitaire de Recherche Clinique et Centre Hospitalier Universitaire, 641 avenue du Doyen Gaston Giraud, 34093 Montpellier, France and 2Laboratoire de Biochimie pédiatrique, Centre Hospitalier Universitaire Paul-Brousse, 69000 Lyon, France Email: Mireille Claustres* - Mireille.Claustres@igh.cnrs.fr; Jean-Pierre Altiéri - Jean-Pierre.Altieri@igh.cnrs.fr; Caroline Guittard - Caroline.Guittard@igh.cnrs.fr; Carine Templin - Carine.Templin@igh.cnrs.fr; Françoise Chevalier-Porst - francoise.chevalier-porst@chu-lyon.fr; Marie Des Georges - Marie.Desgeorges@igh.cnrs.fr * Corresponding author Abstract Background: To contribute further to the classification of three CFTR amino acid changes (p.I148T, p.R74W and p.D1270N) either as CF or CBAVD-causing mutations or as neutral variations. Login to comment 3 ABCC7 p.Ile148Thr ABCC7 p.Ile148Thr Results: Four CF patients (out of 1238) originally identified as carrying the p.I148T mutation in trans with a CF mutation had a second mutation (c.3199del6 or a novel mutation c.3395insA) on the p.I148T allele. Login to comment 4 ABCC7 p.Ile148Thr We demonstrate here that the deletion c.3199del6 can also be associated with CF without p.I148T. Login to comment 5 ABCC7 p.Asp1270Asn ABCC7 p.Asp1270Asn ABCC7 p.Arg74Trp ABCC7 p.Arg74Trp ABCC7 p.Val201Met Three CBAVD patients originally identified with the complex allele p.R74W-p.D1270N were also carrying p.V201M on this allele, by contrast with non CF or asymptomatic individuals including the mother of a CF child, who were carrying p.R74W-p.D1270N alone. Login to comment 6 ABCC7 p.Asp1270Asn ABCC7 p.Arg74Trp ABCC7 p.Ile148Thr Conclusion: These findings question p.I148T or p.R74W-p.D1270N as causing by themselves CF or CBAVD and emphazises the necessity to perform a complete scanning of CFTR genes and to assign the parental alleles when novel missense mutations are identified. Login to comment 15 ABCC7 p.Arg117His ABCC7 p.Arg117His The most striking exemple is the length of the intron 8 polythymidine tract (7, 9, or 5 thymidines) on exon 9 splicing as a genetic modifier of the severity of the p.R117H mutation [1]. Login to comment 16 ABCC7 p.Arg553Gln Another exemple is the revertant mutation p.R553Q which, when carried on the same gene as p.F508del, is associated with a CF phenotype with normal chloride concentration in sweat test [6] and which, when expressed in heterologous cells, can partially correct the processing and Cl-channel gating defects caused by the p.F508del mutation [7]. Login to comment 18 ABCC7 p.Asp1270Asn ABCC7 p.Ile148Thr In North American populations, missense mutations p.I148T and p.D1270N were found >100 times and >200 times, respectively, more frequently in carrier screening than in CF patients [8,9]. Login to comment 19 ABCC7 p.Asp1270Asn ABCC7 p.Arg74Trp ABCC7 p.Arg74Trp Moreover, we and others have found that individuals affected with CF or CBAVD carry p.D1270N associated with p.R74W on the same allele [p.R74W;p.D1270N] [10,11,5]. Login to comment 20 ABCC7 p.Ile148Thr Similarly, p.I148T has been shown to be associated with a CF phenotype only as a complex allele, i.e. when associated with mutation c.3199del6 on the same gene [8]. Login to comment 21 ABCC7 p.Asp1270Asn ABCC7 p.Ile148Thr A completely asymptomatic male individual who is a compound heterozygote for p.D1270N and p.I148T has been recently identified [9]. Login to comment 22 ABCC7 p.Arg74Trp ABCC7 p.Ile148Thr These findings provided evidence that these missense changes may not be the true mutations and prompted us to reanalyze all the patients in our CF or CBAVD cohort who had been originally diagnosed as compound heterozygotes for either p.I148T or [p.R74W;p.D1270N] and another mutation on the other allele. Login to comment 23 ABCC7 p.Asp1270Asn ABCC7 p.Ile148Thr ABCC7 p.Val201Met The result of full scanning of CFTR sequences showed that a second mutation (c.3199del6 or the novel mutation c.3395insA) was associated in cis with p.I148T in all individuals with a CF phenotype, and that a third missense mutation (p.V201M) was associated in cis with complex allele [p.D1270N;p.R74W] in patients with a CBAVD phenotype in this series. Login to comment 24 ABCC7 p.Asp1270Asn ABCC7 p.Ile148Thr Methods CFTR scanning for individuals with p.I148T or [p.D1270N;p.R74W] From 1990 to 2003, we have analysed for CFTR mutations genomic DNA from 437 families with CF and 170 with isolated azoospermia caused by CBAVD, using a combination of mutation screening for known and scanning for unknown mutations. Login to comment 29 ABCC7 p.Arg74Trp ABCC7 p.Ile148Thr In this study, we analyzed by DGGE the entire coding and flanking regions of the CFTR gene of individuals who had been previously found to carry p.I148T or the complex allele [p.R74W;p.D1270N] and assayed their relatives for the additional sequence changes identified. Login to comment 32 ABCC7 p.Ile148Thr In addition, we also reanalyzed two additional CF patients previously found to carry p.I148T in the Lyon genetic center. Login to comment 37 ABCC7 p.Ile148Thr ABCC7 p.Ile148Thr Results A CF mutation (c.3199del6 or c.3395insA) is associated in cis with p.I148T in CF patients Two out of 437 CF patients analyzed in Montpellier and two out of 801 CF patients analyzed in Lyon were found to carry p.I148T, which was initially thought to be one of the two mutations responsible for CF in these patients. Login to comment 39 ABCC7 p.Ile148Thr Mutation c.3199del6 can also occur alone as a CF-causing allele Mutation c.3199del6 was found to be carried without p.I148T in a young CF male with 394delTT on the other allele, diagnosed at the age of 7 years on the basis of typical pulmonary disease, pancreatic insufficiency, poor growth and positive sweat test [12]. Login to comment 46 ABCC7 p.Ile148Thr The familial segregation analysis of polymorphisms covering the CFTR gene showed that p.I148T, when present in individuals with a CF phenotype, occurred on a unique haplotype carrying IVS8-9T whatever the mutation in cis, c.3395insA or c.3199del6 (table 1). Login to comment 47 ABCC7 p.Ile148Thr ABCC7 p.Ile148Thr ABCC7 p.Ile148Thr By contrast, c.3199del6 without p.I148T occurred on a different haplotype carrying IVS8-7T. Mutations p.I148T, c.3199del6 and c.3395insA were not found on 600 chromosomes from our general population. Login to comment 48 ABCC7 p.Arg74Trp ABCC7 p.Arg74Trp ABCC7 p.Arg74Trp ABCC7 p.Val201Met Triple-mutant allele [p.R74W;p.V201M;p.D1270N] is found in males with CBAVD whereas double-mutant allele [p.R74W;p.D1270N] is found in asymptomatic individuals Re-analysis of the CFTR gene in families carrying [p.R74W;p.D1270N] identified a third mutation (p.V201M) on the same chromosome in three unrelated individuals with CBAVD (table 2). Login to comment 49 ABCC7 p.Asp1270Asn ABCC7 p.Arg74Trp Only the double-mutant p.R74W-p.D1270N was present in the two unaffected individuals who were found with these changes in our sample. Login to comment 51 ABCC7 p.Pro67Leu The second individual was the mother of a CF girl who was compound heterozygous for p.F508del and p.P67L. Login to comment 52 ABCC7 p.Asp1270Asn ABCC7 p.Arg74Trp ABCC7 p.Ile148Thr ABCC7 p.Pro67Leu This woman, who was carrying p.P67L on one CFTR gene and [p.R74W-p.D1270N] on the other (table 1), was completely asymptomatic at age 45 years Table 1: CFTR haplotypes associated with mutations found in CF patients carrying p.I148T in cis with c.3395insA or c.3199del6 and in one CF patient carrying c.3199del6 alone Indiv No. Login to comment 53 ABCC7 p.Arg334Trp Age at Diagnosis Phenotype CFTR Mutations CFTR haplotype IVS1 IVS8 IVS8 IVS8 470 IVS17B IVS17B EGHa CA CA TGm Tn TA CA CF1 7 yrs CF-PI c.394delTT 21 23 10 9 M 36 13 B c.3199del6 22 16 11 7 V 7 17 C CF2 10 yrs CF-PS [c.3395insA;p.I148T] 21 23 10 9 M 7 17 B p.R334W 22 17 11 7 V 46 13 A CF3 6 ms CF-PI [c.3199del6;p.I148T] 21 23 10 9 M 7 17 B p.F508del 21 23 10 9 M 31 13 B CF4 3 yrs CF-PI [c.3199del6;p.I148T] 22 23 nd 9 M 7 17 B p.F508del 22 17 nd 9 M 31 15 B CF5 6 ms CF-PI [c.3199del6;p.I148T] 22 23 nd 9 M 7 17 B p.F508del 22 23 nd 9 M 31 13 B aEGH, extragenic haplotype XV2c/TaqI, KM19/PstI ; nd, not determined Patients CF1-3 were from the cohort of Montpellier (n = 437), patients CF4-5 were from the cohort of Lyon (n= 801). Login to comment 56 ABCC7 p.Ile148Thr ABCC7 p.Ile148Thr Discussion p.I148T is a low penetrance CF mutation or a neutral polymorphism Since its initial description in a CF Canadian patient with pancreatic insufficiency [16], the mutation p.I148T, which changes a conserved amino acid and occurs in the first cytoplasmic loop of the CFTR protein, has been considered as a severe CF allele in many countries. Login to comment 57 ABCC7 p.Ile148Thr It was thought to be the second most common CF mutation in the French Canadian population, accounting for 9.1% of the French Canadian chromosomes [17], whereas in France, p.I148T accounted for only 0.11 % of the CF alleles in a sample of 3,710 patients affected with the disease [5]. Login to comment 58 ABCC7 p.Ile148Thr p.I148T can now be detected by several commercially available kits developed for routine screening of CF carriers and for CF neonatal screening, and recently it has been included in the core panel of 25 CF mutations recommended by the American College of Medical Genetics (ACMG) [18]. Login to comment 60 ABCC7 p.Ile148Thr However there are now several lines of evidence that question the role of p.I148T by itself in causing disease. Login to comment 61 ABCC7 p.Ile148Thr First, compound heterozygosity for p.I148T and a severe CF mutation was recently identified in several healthy individuals [9,19]. Login to comment 62 ABCC7 p.Ile148Thr ABCC7 p.Ile148Thr ABCC7 p.Ile148Thr When affected and unaffected individuals carrying apparently the same mutational genotype were re-analyzed for additional changes that could explain the different phenotypes, p.I148T was found to be associated in cis with another mutation, c.3199del6, in patients with a classic CF phenotype, whereas healthy adults who were compound heterozygous for p.I148T and a severe CF mutation or homozygous for p.I148T did not carry the deletion [8]. Login to comment 63 ABCC7 p.Ile148Thr ABCC7 p.Ile148Thr In a recent study, the p.I148T mutation has been further documented to be linked with the 3199del6 mutation in all 24 CF patients of French Canadian descent originally identified as compound heterozygous for the p.I148T mutation and a second severe CFTR mutation [20]. Login to comment 64 ABCC7 p.Ile148Thr Second, p.I148T was found to be over 100 times more common in two independent U.S. carrier screening programmes than in CF patients: it accounted for 6.4 to 7.7% of chromosomes detected in the screened populations versus 0.06 to 0.068% of CF chromosomes in CF patients [8. Login to comment 66 ABCC7 p.Ile148Thr This discrepancy suggests that p.I148T is either a poorly penetrant mutation or a neutral polymorphism. Login to comment 67 ABCC7 p.Ile148Thr Third, when transiently expressed in epithelial cells, p.I148T mutant protein is normally processed and is able to mediate normal chloride transport with properties identical with those of wild-type cells [21]. Login to comment 68 ABCC7 p.Ile148Thr ABCC7 p.Ile148Thr As the mutant seems to suppress the ability of CFTR to support HCO3-transport, it has been hypothesized that p.I148T may contribute to disease through Cl- coupled HCO3- altered transport; however, the major CFTR functions are retained by the mutant [21]. Login to comment 69 ABCC7 p.Ile148Thr Fourth, we show in this study for the first time that p.I148T can be associated with a frameshift mutation c.3395insA in exon 17b instead of in-frame deletion c.3199del6 in exon 17a. Login to comment 72 ABCC7 p.Asp1270Asn ABCC7 p.Arg74Trp ABCC7 p.Arg74Trp ABCC7 p.Arg74Trp ABCC7 p.Arg74Trp ABCC7 p.Arg74Trp ABCC7 p.Arg74Trp ABCC7 p.Pro67Leu ABCC7 p.Arg1066Cys ABCC7 p.Met952Ile ABCC7 p.Val201Met A CFTR alteration producing a premature termination signal is a class I mutation, considered severe enough to cause CF by itself and exclude the contribution of any other sequence Table 2: CFTR sequence changes found in individuals carrying missense alterations p.R74W, p.D1270N, or p.V201M Mutations Haplotype IVS1 IVS8 IVS8 IVS8 470 IVS17B IVS17B CA CA TGm Tn TA CA CBAVD1 p.R1066C 22 16 11 7 V 30 13 [p.R74W;p.V201M;p.D1270N] 22 16 11 7 V 31 13 CBAVD2 p.M952I 26 17 10 7 M 7 17 [p.R74W;p.V201M;p.D1270N] 22 16 11 7 V 31 13 CBAVD3 [p.R74W;p.V201M;p.D1270N] 22 16 11 7 V 31 13 [p.R74W;p.V201M;p.D1270N] 22 16 11 7 V 31 13 Individual non affected with CF No mutation 21 nd 10 7 M 7 17 [p.R74W;p.D1270N] 22 nd 11 7 V 30 13 Asymptomatic mother of a CF affected girl p.P67L 23 16 10 7 M 7 17 [p.R74;p.D1270N] 22 16 11 7 V 31 13 change on the same allele. Login to comment 73 ABCC7 p.Ile148Thr ABCC7 p.Ile148Thr ABCC7 p.Ile148Thr Fifth, in contrast with other studies that stated that only the complex allele [p.I148T;9T;c.3199del6] appeared to be associated with a classic CF phenotype [8], we demonstrate that c.3199del6 is associated with a CF phenotype even if the deletion occurs on a chromosome that does not carry p.I148T, which adds further value to the consideration that p.I148T is not a true mutation but simply a polymorphism. Login to comment 75 ABCC7 p.Ile148Thr Our data fully support the recent recommendation that p.I148T should not be included in the mutation panel selected for prenatal screening strategy [22]. Login to comment 76 ABCC7 p.Asp1270Asn ABCC7 p.Arg74Trp ABCC7 p.Arg74Trp The complex allele [p.R74W;p.D1270N] may be not enough to cause disease We and others had initially described p.R74W [23] and p.D1270N [24] in isolation but they have since been found in association in many CBAVD or CF patients [10,11] and these two changes were thought to be deleterious, alone or in combination. Login to comment 78 ABCC7 p.Asp1270Asn ABCC7 p.Arg74Trp ABCC7 p.Arg74Trp ABCC7 p.Arg74Trp When expressed in HeLa cells, mutant p.R74W, p.D1270N and [p.R74W;p.D1270N] did not affect CFTR processing, however a lower cAMP-responsive anion conductance was observed with the double mutant [p.R74W;p.D1270N] [3]. Login to comment 79 ABCC7 p.Asp1270Asn ABCC7 p.Asp1270Asn ABCC7 p.Arg74Trp ABCC7 p.Arg74Trp The assay suggested that p.R74W alone should be considered as a polymorphism, p.D1270N alone could generate a CBAVD phenotype while the complex allele could produce a more severe phenotype as p.R74W could enhance the effect of p.D1270N [3]. Login to comment 81 ABCC7 p.Arg74Trp ABCC7 p.Arg74Trp We have found here that a triple-mutant [p.R74W;p.V201M;p.D1270N] allele was carried in all three patients with CBAVD whereas only the double mutant [p.R74W;p.D1270N] allele was present in two asymptomatic individuals including an obligate carrier who was compound heterozygous for a CF mutation. Login to comment 82 ABCC7 p.Arg74Trp Another mother carrying [p.R74W;p.D1270N] in trans of a CF mutation has been described previously; despite two positive sweat tests she was absolutely asymptomatic [25]. Login to comment 83 ABCC7 p.Val201Met Missense p.V201M in exon 6a changes a valine for a methionine in the third transmembrane domain; it was initially reported alone in a French patient with CBAVD [26], then in Brazilian patients with CF [27]. Login to comment 84 ABCC7 p.Asp1270Asn ABCC7 p.Asp1270Asn ABCC7 p.Ile148Thr Recent large scale screening for CF carrier showed that p.D1270N was present 205 times more commonly in the screened population than in the CF patients (frequency of 14% versus 0.068%); in addition, a completely asymptomatic adult compound heterozygote for p.D1270N and p.I148T has been identified [9]. Login to comment 85 ABCC7 p.Arg74Trp ABCC7 p.Val201Met Although it is not known whether these alleles are associated or not with the third change p.V201M, there are now enough evidence to question the role of the complex allele [p.R74W;p.D1270N] as being a CF or CBAVD mutation. Login to comment 86 ABCC7 p.Val201Met Further experimental and genetic investigations will be necessary to demonstrate the role of p.V201M in causing disease. Login to comment 87 ABCC7 p.Asp1270Asn ABCC7 p.Arg74Trp ABCC7 p.Ile148Thr Conclusions This report further corroborates the recent hypothesis [9] that p.I148T and p.R74W-p.D1270N may not be true CF/ CBAVD mutations. Login to comment 88 ABCC7 p.Arg74Trp ABCC7 p.Ile148Thr If these observations are further confirmed by a large multicentric study, they will have important implications for genetic counseling of patients and couples found to carry p.I148T or [p.R74W;p.D1270N]. Login to comment