Novel CFTR mutations in black cystic fibrosis patients

Cystic fibrosis (CF) is considered as a rare disease in black Africans. In fact, this disease is likely to be underestimated since clinical features consistent with CF diagnosis are often ascribed to environmental factors such as malnutrition. Very little is known about CFTR mutations in affected patients from Central Africa. We report here four novel mutations, i.e., IVS2 + 28 (intron 2), 459T > A (exon 4), EX17a_EX18del (exons 17-18), and IVS22 + IG > A (intron 22), in such patients. An update of CFTR mutations reported in black patients from various ethnies is included. These data might be helpful for genetic counselling regarding CF in black patients.     

Spectrum of CFTR mutations in cystic fibrosis and in congenital absence of the vas deferens in France

We have collated the results of cystic fibrosis (CF) mutation analysis conducted in 19 laboratories in France. We have analyzed 7, 420 CF alleles, demonstrating a total of 310 different mutations including 24 not reported previously, accounting for 93.56% of CF genes. The most common were F508del (67.18%; range 61-80), G542X (2.86%; range 1-6.7%), N1303K (2.10%; range 0.75-4.6%), and 1717-1G>A (1.31%; range 0-2.8%). Only 11 mutations had relative frequencies >0. 4%, 140 mutations were found on a small number of CF alleles (from 29 to two), and 154 were unique. These data show a clear geographical and/or ethnic variation in the distribution of the most common CF mutations. This spectrum of CF mutations, the largest ever reported in one country, has generated 481 different genotypes. We also investigated a cohort of 800 French men with congenital bilateral absence of the vas deferens (CBAVD) and identified a total of 137 different CFTR mutations. Screening for the most common CF defects in addition to assessment for IVS8-5T allowed us to detect two mutations in 47.63% and one in 24.63% of CBAVD patients. In a subset of 327 CBAVD men who were more extensively investigated through the scanning of coding/flanking sequences, 516 of 654 (78. 90%) alleles were identified, with 15.90% and 70.95% of patients carrying one or two mutations, respectively, and only 13.15% without any detectable CFTR abnormality. The distribution of genotypes, classified according to the expected effect of their mutations on CFTR protein, clearly differed between both populations. CF patients had two severe mutations (87.77%) or one severe and one mild/variable mutation (11.33%), whereas CBAVD men had either a severe and a mild/variable (87.89%) or two mild/variable (11.57%) mutations.     

Spectrum of CFTR mutations in Argentine cystic fibrosis patients

The identification of different mutations which cause cystic fibrosis (CF) in Argentine patients has been performed. Initially, 10 of the most commonly mutated loci in 228 independent chromosomes were analyzed. Each allele was detected by PCR amplification of DNA samples either directly on polyacrylamide gels, by restriction enzyme digestion and agarose gels electrophoresis, or by hybridization with allele specific oligonucleotides. The AF508 mutation was found in 57% of the alleles. The frequencies of the other CF mutations were as follows: G542X 3.9%, W1282X 3.1%, N1303K 1.7%, 1717 1-G→A 0.9%, R553X 0.4%, R1162X 0.4%, whereas G551D, AI507 and S549N were not found. This direct mutation analysis enabled the detection of 155/228 CF alleles (67%). Of the remaining 73 unidentified CF alleles, 22 were investigated for the 27 exons by DGGE and 9 rare mutations were identified. The incidence of the main CF mutations analyzed was similar to that of the South European population and markedly different from other Latin American countries. The mutation data presented here may be useful for designing DNA testing strategies for CF in Argentina.     

CFTR与囊性纤维化

囊性纤维化跨膜传导调节因子（CFTR）是一种cAMP激活的ATP门控性氯离子通道,表达于气道,消化道和生殖道上皮细胞的顶部质膜中。囊性纤维化(CF)是白人中最常见的遗传性疾病之一,由CFTR基因突变造成。对CFTR基因的破译使人们进一步了解CF的发病机制,并为该疾病的诊断提供了新的线索。     

Mild CFTR mutations and genetic predisposition to lactase persistence in cystic fibrosis

Taking into account the reported incidence of hypolactasia in cystic fibrosis (CF) and the possible impact of milk products on nutritional status we aimed to assess the genetic predisposition to adult-type hypolactasia (ATH) and its incidence in CF. Single nucleotide polymorphism upstream of the lactase gene (LCT) was assessed in 289 CF patients. In subject with -13910C/C genotype (C/C) predisposing to ATH, hydrogen-methane breath test (BT) with lactose loading was conducted and clinical symptoms typical for lactose malabsorption were assessed. The percentage of CF patients with C/C was similar to that observed in healthy subjects (HS) (31.5 vs 32.5% ). Eleven out of 52 (24.5%) CF C/C patients had abnormal BT results. The recalculated frequency of lactose malabsorption was similar for the entire CF and HS populations (6.9 vs 7.2%). Similarly as in the control group, few CF patients have identified and linked to lactose consumption clinical symptoms. The frequency of LCT polymorphic variants in CF patients having and not having severe mutations of CFTR gene showed significant differences. The C allele was more frequent in homozygotes of the severe mutations than in patients carrying at least one mild/unknown mutation (P<0.0028) and in patients with at least one mild mutation (P < 0.0377). In conclusion, CF patients carrying mild CFTR mutations seem to have lower genetic predisposition to ATH. Lactose malabsorption due to ATH in CF is not more frequent than in the general population. Symptomatic assessment of lactose malabsorption in CF is not reliable.     

Prevalence of CFTR mutations in hypertrypsinaemia detected through neonatal screening for cystic fibrosis

Nowadays, most of the neonatal screening programs for cystic fibrosis (CF) combine the assay of immunoreactive trypsinogen (IRT) with the analysis of the most common mutations of the CFTR gene. The efficiency of this strategy is now well established, but the identification of heterozygotes among neonates with increased IRT is perceived as a drawback. We proposed to assess the heterozygosity frequency among the children with hypertrypsinaemia detected through the CF screening program implemented in Brittany (France) 10 years ago, to describe the CFTR mutations detected in them and to determine the frequency of the IVS8-5T variant. The molecular analysis relies, in our protocol, on the systematic analysis of three exons of the gene (7-10-11). A total of 160,019 babies were screened for CF in western Brittany between 1992 and 1998. Of the 1964 newborns with increased IRT (1.2%), 60 were CF and 213 were carriers. Heterozygosity frequency was 12.8%), i.e. 3 times greater than in the general population (3.9%; p < 10(-6)), Variability of mutations detected in carriers was greater than in CF children (21 mutations versus 10) and a high proportion of mild mutations or variants (A349V, R297Q, R347H, V317A, G544S, R553G, etc) was observed in carriers. The allelic frequency of the 5T (5.6%) was not significantly increased in this cohort. This study is consistent with previous ones in finding a significantly higher rate of heterozygotes than expected among neonates with hypertrypsinaemia. The strategy of screening used here allows to highlight the variability of mutations detected in heterozygotes and to show that severe mutations, as well as mild mutations, have been observed in neonates with hypertrypsinaemia. If there is no doubt that neonatal hypertrypsinaemia is associated with an elevated frequency of carriers, the underlying mechanisms remain obscure.     

Haplotype analysis of 94 cystic fibrosis mutations with seven polymorphic CFTR DNA markers

We have analyzed 416 normal and 467 chromosomes carrying 94 different cystic fibrosis (CF) mutations with polymorphic genetic markers J44, IVS6aGATT, IVS8CA, T854, IVS17BTA, IVS17BCA, and TUB20. The number of mutations found with each haplotype is proportional to its frequency among normal chromosomes, suggesting that there is no preferential haplotype in which mutations arise and thus excluding possible selection for specific haplotypes. While many common mutations in the worldwide CF population showed absence of haplotype variation, indicating their recent origins, some mutations were associated with more than one haplotype. The most common CF mutations, ΔF508, G542X, and N1303K, showed the highest number of slippage events at microsatellites, suggesting that they are the most ancient CF mutations. Recurrence was probably the case for 9 CF mutations (R117H, H199Y, R347YH, R347P, L558S, 2184insA, 3272-26A → G, R1162X, and 3849 + 10kbC → T). This analysis of 94 CF mutations should facilitate mutation screening and provides useful data for studies on population genetics of CF. © 1996 Wiley-Liss, Inc.     

Novel and characteristic CFTR mutations in Saudi Arab children with severe cystic fibrosis.

More than 600 different CFTR (cystic fibrosis transmembrane conductance regulator) gene mutations have been identified so far that are considered to cause the fatal genetic disorder cystic fibrosis (CF). We have investigated 15 Arab children from 12 families, who were diagnosed as having CF, for mutations in the coding region and in the flanking intron sequences of the CFTR gene. Six different CFTR mutations were identified including two novel mutations, 1548delG in exon 10 and 406-2A-->G in intron 3. Prominent mutations were the splice mutation 3120 + 1G-->A (intron 16) followed by N1303K (exon 21) and 1548delG (exon 10). Most CF children were homozygotes who presented with a severe form of the disease including failure to thrive, recurrent chest infections, particularly with Pseudomonas aeruginosa, and frequent hospital admissions. Identification of the CFTR mutations facilitates molecular investigation of the disease and better understanding of its pathophysiology in Arab children, among whom CF is probably an underdiagnosed disease.     

First report of CFTR mutations in black cystic fibrosis patients of southern African origin.

Cystic fibrosis (CF) is thought to be rare in the black populations of Africa who have minimal white admixture. Only a few cases have been reported but have not been studied at the molecular level. We report the detection of CFTR mutations in three southern African black patients. One was homozygous for the 3120 + 1G-->A mutation, while the other two were compound heterozygotes each with this mutation on one chromosome. The other mutations were G1249E and a previously unreported in frame 54 bp deletion within exon 17a involving nucleotides 3196-3249 (3196del54). The 3120 + 1G-->A mutation was first described in American black patients and has been shown to be a common mutation in this population (9-14% of CF chromosomes). It was also found in a black CF patient whose father, the 3120 + 1G-->A carrier, is from Cameroon. These data suggest that it is an old mutation which accounts for many of the CFTR mutations in African blacks.     

A cluster of cystic fibrosis mutations in exon 17b of the CFTR gene: a site for rare mutations.

Intensive screening has improved our understanding of the profile of mutations in the CFTR gene in which more than 400 mutations have been detected to date. In collaboration with several European laboratories we are involved in such analysis. We have identified 14 new mutations in exon 17b of CFTR, having analysed 780 CF chromosomes, and have compared the frequency of mutations in this exon with that of other regions of the CFTR gene. The results obtained indicate an accumulation of mutations, not only in regions encoding the two nucleotide binding folds, but also in those encoding transmembrane domains of the CFTR gene, in particular exon 17b.     

First report of cystic fibrosis mutations in Libyan cystic fibrosis patients

Background: There are few data on the molecular basis of Cystic Fibrosis (CF) in North Africa, probably due to under-diagnosis.

Aim: This is the first study of cystic fibrosis transmembrane conductance regulator (CFTR) mutations in the Libyan population.

Subjects and methods: This study analysed the complete coding region and flanking intronic sequences of the CFTR gene in 10 unrelated Libyan CF patients.

Results: This study identified four mutations (F508del, c.1670delC, N1303K and E1104X), with a high frequency of the latter.

Conclusion: Identification of CF mutations facilitates molecular investigation of cystic fibrosis in the Libyan population and helps to provide effective genetic counselling among CF families.