Cystic fibrosis mutations in French Canadians: Three CFTR mutations are relatively frequent in a Quebec population with an elevated incidence of cystic fibrosis

The French-Canadian population in the Saguenay-Lac St. Jean region of northeastern Quebec has an elevated frequency of cystic fibrosis (CF). The average incidence of cystic fibrosis was 1 in 891 births and the prevalence of CF carriers was estimated to be 1 in 15. We tested for 10 mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene in 133 French-Canadian CF families from Quebec. Ninety-one families were from the Saguenay-Lac St. Jean region and 42 families were referred from other regions of Quebec. We detected the CFTR mutation in 93 and 92% of the CF chromosomes in the Saguenay-Lac St. Jean and the major-urban Quebec families, respectively. The two groups of French-Canadian families were significantly different for the proportions of CFTR mutations. The three most common mutations in the Saguenay-Lac St. Jean families were ΔF508 (58%), 621 + 1G → T (23%), and A455E (8%); and in the major-urban Quebec families were ΔF508 (71%), 711 + 1G → T (9%), and 621 + 1G → T (5%). These results provide evidence for the role of founder effect in the elevated incidence of cystic fibrosis in the Saguenay-Lac St. Jean population.     

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.     

Cystic fibrosis mutations in French Canadians: three CFTR mutations are relatively frequent in a Quebec population with an elevated incidence of cystic fibrosis.

The French-Canadian population in the Saguenay-Lac St. Jean region of northeastern Quebec has an elevated frequency of cystic fibrosis (CF). The average incidence of cystic fibrosis was 1 in 891 births and the prevalence of CF carriers was estimated to be 1 in 15. We tested for 10 mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene in 133 French-Canadian CF families from Quebec. Ninety-one families were from the Saguenay-Lac St. Jean region and 42 families were referred from other regions of Quebec. We detected the CFTR mutation in 93 and 92% of the CF chromosomes in the Saguenay-Lac St. Jean and the major-urban Quebec families, respectively. The two groups of French-Canadian families were significantly different for the proportions of CFTR mutations. The three most common mutations in the Saguenay-Lac St. Jean families were delta F508 (58%), 621 + 1G----T (23%), and A455E (8%); and in the major-urban Quebec families were delta F508 (71%), 711 + 1G----T (9%), and 621 + 1G----T (5%). These results provide evidence for the role of founder effect in the elevated incidence of cystic fibrosis in the Saguenay-Lac St. Jean population.     

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。     

Increased incidence of cystic fibrosis gene mutations in adults with disseminated bronchiectasis

In order to identify a possible hereditary predisposition tothe development of obstructive pulmonary disease of unknownorigin, we have looked for the presence of Cystic Fibrosis TransmembraneRegu lator (CFTR) gene mutations in unrelated patients withno signs of Cystic Fibrosis (CF). We screened for 70 commonmutations, and also for rare mutations by denaturing gradientgel electrophoresis analysis. In this search, different CFTRgene mutations (R75Q,     

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.     

Complete screening of the CFTR gene in Argentine cystic fibrosis patients

In order to establish the nature and the distribution of mutations causing cystic fibrosis (CF) in 220 unrelated Argentine families, the present authors conducted an extensive molecular analysis of the CF transmembrane regulator (CFTR) gene. First, a direct mutation analysis of 13 common mutations was done, enabling the detection of 319 out of 440 CF alleles (72.52%). Then an exhaustive screening of the entire coding region and the adjacent sequences of the CFTR gene was performed in all patients carrying at least one unidentified CF allele using the multiplex heteroduplex analysis assay followed by direct DNA sequencing. Thirty-nine different CF mutations, including five previously undescribed mutations (i.e. L6V, Y362X, 1353insT, 2594delGT and 2686insT) and two novel polymorphisms (i.e. 1170G/C and 3315A/C) were identified. As a result, the overall detection rate increased by up to 83.45%. Besides DeltaF508, only five mutations showed frequencies higher than 1%. In addition, a total of 49% of the mutations were rare because they were found in only one CF family. This wide spectrum of CF mutations is in agreement with the heterogeneous ethnic origin of the Argentine population. The data obtained here may have important consequences for the development of adequate strategies for the molecular diagnosis of CF in Argentina.     

Gene mutations of cystic fibrosis in Brittany population

Eighty percent of chromosomes from cystic fibrosis children in Brittany exhibit the major gene mutation (delta F 508) consisting in deletion of three nucleotide pairs. Eighty-seven chromosomes without the delta F 508 mutation were studied for as yet undescribed gene mutations. A large number of mutations were located in exons 10 and 11. Consequently, a global strategy for identifying mutations in these exons was developed. Analysis of pedigrees of cystic fibrosis patients in Brittany evidenced a clear founder effect. Appropriate prevention strategies will therefore be developed.     

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.     

DHPLC screening of cystic fibrosis gene mutations

Denaturing high performance liquid chromatography (DHPLC) using ion-pairing reverse phase chromatography (IPRPC) columns is a technique for the screening of gene mutations. In order to evaluate the potential utility of this assay method in a clinical laboratory setting, we subjected the PCR products of 73 CF patients known to bear CFTR mutations to this analytic technique. We used thermal denaturation profile parameters specified by the MELT program tool, made available by Stanford University. Using this strategy, we determined an initial analytic sensitivity of 90.4% for any of 73 known CFTR mutations. Most of the mutations not detected by DHPLC under these conditions are alpha-substitutions. This information may eventually help to improve the MELT algorithm. Increasing column denaturation temperatures for one or two degrees above those recommended by the MELT program allowed 100% detection of CFTR mutations tested. By comparing DHPLC methodology used in this study with the recently reported study based on Wavemaker 3.4.4 software (Transgenomic, Omaha, NE) [Le Marechal et al., 2001) and with previous SSCP analysis of CFTR mutations [Ravnik-Glavac et al., 1994] we emphasized differences and similarities in order to refine the DHPLC system and discuss the relationship to the alternative approaches. We conclude that the DHPLC method, under optimized conditions, is highly accurate, rapid, and efficient in detecting mutations in the CFTR gene and may find high utility in screening individuals for CFTR mutations. Hum Mutat 19:374-383, 2002. Published 2002 Wiley-Liss, Inc.     

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.     

Rapid characterization of the variable length polythymidine tract in the cystic fibrosis (CFTR) gene: Association of the 5T allele with selected CFTR mutations and its incidence in atypical sinopulmonary disease

The CFTR intron 8 variable length polythymidine tract modulates the cystic fibrosis (CF) phenotype associated with the mutation R117H. To explore whether other mutations reside on multiple intron 8 backgrounds with discernible impacts on phenotype, we developed an allele-specific PCR assay to characterize this locus. Our approach types samples rapidly without the use of radioisotopes. Polythymidine alleles were identified for mutations either associated with a wide range of clinical phenotypes (R117H, R347P, G85E, D1152H, R334W, 2789+5 G>A, 3849+10kb C>T), and/or located at hypermutable CpG loci (R117H, 3849+10kb C>T, R553X, R334W, S945L and R75Q). R117H was detected in cis with each of three alleles (5T, 7T, 9T) at the intron 8 locus. The novel R117H-9T association was detected in a 10-month old African-American male with borderline-to-mildly elevated sweat chloride values (˜50–66 mEq/L). All other mutations studied were associated with 7T except 3849+10kb C>T, which was detected on both 7T and 9T backgrounds, but not 5T. Three individuals with a ΔF508/3849+10kb C>T genotype were 9T,9T and had pancreatic sufficiency and normal sweat chloride values, whereas 15 others who carried 3849+10kb C>T on a 7T background had variable pancreatic function (sufficient, n = 12, insufficient, n = 3), and variable sweat chloride values (normal, n = 12, elevated, n = 3). Surprisingly, when not associated with known CFTR mutations, 5T was detected with elevated frequency among individuals with sinopulmonary disease of ill-defined etiology, but with some characteristics of variant CF. In summary, the 5T allele was not found in cis with CF-causing mutations besides R117H, but an elevated 5T allele frequency in variant CF patients suggests 5T may be associated with disease in some situations. Hum Mutat 10:108–115, 1997. © 1997 Wiley-Liss, Inc.     

Single-stranded conformation polymorphism analysis of the CFTR gene in slovenian cystic fibrosis patients: Detection of mutations and sequence variations

Cystic fibrosis (CF) mutations have been identified in Slovenian CF patients using single-stranded conformation polymorphism (SSCP) analysis. The entire coding region and all of the splice junction sites were screened in 24 patients. By varying the electrophoretic conditions and composition of the gel, 16 different nucleotide changes have been observed in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. Three newly described mutations and four previously reported mutations were found. In addition two new polymorphisms have been identified. Of 35 non-ΔF508 chromosomes examined, mutations were detected on 25.7%, raising the proportion of Slovenian CF alleles characterized to 67.5%. Because of the high sensitivity of the SSCP technique most of the remaining uncharacterized CF mutations probably lie in large introns, promoter sequences, or putative regulatory regions not yet analyzed. © 1993 Wiley-Liss, Inc.