ABCMdb

PMID: 8844211

Duarte A, Amaral M, Barreto C, Pacheco P, Lavinha J
Complex cystic fibrosis allele R334W-R1158X results in reduced levels of correctly processed mRNA in a pancreatic sufficient patient.
Hum Mutat. 1996;8(2):134-9., [PubMed]

Sentences

No. Mutations Sentence Comment

4 ABCC7 p.Arg334Trp ABCC7 p.Arg1158* Here, we describe a three-generation CF family with a complex CFTR allele that has not been previously described, containing the missense mutation R334W in exon 7 and the nonsense mutation R1158X in exon 19. Login to comment 18 ABCC7 p.Arg334Trp INC. COMPLEX CFIll ALLELE IN A PANCREATIC-SUFFICIENTPATIENT I 1 FIGURE1.Pedigreeof a Portuguesefamily with the complexallele R334W-Rl158X Results of mutation and haplotype analysis performed in the family members are shown beneath each symbol. Login to comment 34 ABCC7 p.Arg334Trp ABCC7 p.Arg1158* Direct DNA sequencing of exons 7 and 19 revealed the presence of two mutations previously described in separate, namely R334W in exon 7 (Gasparini et al., 1991)and R1158X in exon 19 (Ronchetto et al., 1992). Login to comment 37 ABCC7 p.Arg553Gln ABCC7 p.Val1212Ile The first published complex allele in the CFTR gene (Dork et al., 1991) consisted of an alteration (R553Q) that partially reverted the phenotypic effects of the AF508 mutation (Teem et al., 1993).The sameseems to apply to the AF508- V1212I allele (Macek et al., 1993). Login to comment 38 ABCC7 p.Asp1270Asn ABCC7 p.Arg74Trp ABCC7 p.Ser1235Arg ABCC7 p.Phe508Cys ABCC7 p.Gly628Arg Other in cis missense mutations have been reported, namely F508C-Sl251N (Kalin et al., 1992), G628R- S1235R (Mercier et al., 1995) and R74W- D1270N (Verlingue et al., 1993). Login to comment 42 ABCC7 p.Arg334Trp In fact, R334W is a relatively common mutation associated with a mild phenotype. Login to comment 44 ABCC7 p.Arg334Trp The recurrence of R334W (a C-+T transition on a CpG dinucleotide) has been suggestedon the basis of its linkage with haplotypes A and B (Morral et al., 1994). Login to comment 45 ABCC7 p.Arg334Trp The occurrence of R334W in this complex allele on haplotype C may represent yet another independent mutational event. Login to comment 46 ABCC7 p.Arg1158* On the other hand, R1158X as a nonsense mutation, would be expected to cause notorious effects upon protein production or function, either by leading to mRNA instability (Lim et al., 1992), synthesis of a labile truncated protein (Fei et al., 1989), or skipping of the exon in which it is located (Dietz et al., 1993). Login to comment 48 ABCC7 p.Arg334Trp In order to assess the presence and relative amounts of the transcripts from the two CF alleles, the RT-PCR product covering exons 7-13 was tested for R334W and AF508 mutations by MspI digestion and dot-blot AS0 hybridization, respectively (Fig. 2A,B). Login to comment 49 ABCC7 p.Arg334Trp ABCC7 p.Arg1158* Both experiments showed that the mRNA corresponding to the transcript from the R334W- R1158X complex allele was present, although markedly reduced as compared with the transcript from the AF508 allele. Login to comment 50 ABCC7 p.Arg1158* On the other hand, amplification of the fragment containing exon 19 (Fig 2C) showed a single, normal-sizeband, indicating that the R1158X mutation does not lead to detectable skipping of exon 19. Login to comment 54 ABCC7 p.Arg334Trp Following that classification, the AF508 mutation is a PI allele (Keremet al., 1989),whereas the R334W has been found to be PS (Kristidis et al., 1992). Login to comment 55 ABCC7 p.Arg1158* In what concerns the R1158X, as a nonsense mutation, it would be expected to be a PI allele. Login to comment 56 ABCC7 p.Arg1158* Indeed, one CF patient with AF508/ R1158X genotype was found to have severe digestive symptoms (L. Cremonesi, personal communication). Login to comment 57 ABCC7 p.Arg334Trp ABCC7 p.Arg334Trp ABCC7 p.Arg1158* It is therefore noteworthy that the complex allele R334W-Rl158X is PS, suggesting that the R334W mutation in cis with R1158X can, at least partially, revert the deleterious effects caused by the latter. Login to comment 59 ABCC7 p.Arg334Trp ABCC7 p.Arg1158* 4 5 1 2 3 4 CFTR cDNA C 1 2 3 R334W -508 R1158X I1 1 3 4 5 6a 6b 7 8 9 10 1 1 1 2 13 BlL+ t B l R B2R+ t B 2 R FIGURE2. Login to comment 65 ABCC7 p.Arg334Trp A Detection of R334W mutation by MspI digestion. Login to comment 67 ABCC7 p.Arg334Trp The in association with the R334W-Rl158X complex allele. Login to comment 68 ABCC7 p.Arg334Trp First, the presence of alternative splicing, somehow favoured conformationally by the presence in cis of the R334W mutation, could minimize the effect of the Rl158X mutation. Login to comment 72 ABCC7 p.Arg334Trp Nevertheless, a tissue-specific alternative splicing (Tsui and Buchwald, 1991), involving only pancreatic epithelial cells cannot 148 b I5 16 178 1% 18 19 20 21 22 23 24 EXmr IlL+ t I l R I2L+ t 12R faint band of 898 bp observed (lane2) corresponds to the presence of R334W mutation, which abolishes a Mspl restriction site; lane 5, DNA size marker c$ X174+HaeIII. Login to comment 80 ABCC7 p.Asp836* The fact that a truncated CFTR protein may have conductive properties was shown by the Iowa group (Sheppard et al., 1994) for the CETR protein resulting from the D836X mutation (exon 14a), which contains only its N-terminal part (the membrane-spanning domains 1-6, the first ATP-binding fold, and the regulatoryregion). Login to comment 82 ABCC7 p.Arg1158* Similarly, the truncated R1158X CFTR AL. protein might as well function as a C1` channel. Login to comment 84 ABCC7 p.Arg334Trp ABCC7 p.Arg1158* However, the presence of R334W in cis with R1158X might somehow stabilize such truncated CFTR protein, thus conferring the mild pancreatic symptoms found in these two patients. Login to comment