Variations of the CFTR gene in the Hanoi-Vietnamese

In order to investigate polymorphic backgrounds of the cystic fibrosis transmembrane conductance regulator gene (CFTR) in the Vietnamese, we analyzed 495 blood samples of randomly selected healthy individuals in Hanoi for the delta F508 mutation and TG-repeats, poly-T, and M470V polymorphisms. We compared their distributions with those of Caucasians and other Asian populations. No delta F508 mutation was found, being consistent with the extremely low incidence of cystic fibrosis (CF) in Vietnam. Allele frequency of the T5 allele promoting exon 9 skipping was 0.037. Greater number of TG-repeats, which is known to facilitate this aberrant splicing, was a predominant trend in the Vietnamese and other Asians. A "T5-TG12-V470" haplotype was most common (29/37) among T5-bearing haplotypes. Three major haplotypes, T7-TG12-M470, T7-TG11-V470, and T7-TG12-V470, estimated by PHASE program, related to 92% of the population. This is the first study of the CFTR gene among the Vietnamese.     

Molecular analysis of the IVS8-T splice variant 5T and M470V exon 10 missense polymorphism in Iranian males with congenital bilateral absence of the vas deferens

Congenital bilateral absence of the vas deferens (CBAVD) is responsible for 2-6% of male infertility in which mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene have been identified. To investigate CBAVD at the molecular level in Iran, we have characterized the mutations in the CFTR gene in 106 patients with this condition. None had clinical manifestations of cystic fibrosis (CF). We also analysed a DNA variant (the 5T allele) in a noncoding region of CFTR, which causes reduced levels of the normal CFTR protein and M470V exon 10 missense polymorphism. Five of the 106 patients with CBAVD had mutations in both copies of the CFTR gene, and none of them had the 5T allele. Eighty-five patients had a mutation in at least one copy of CFTR, and of these patients, 46 had one 5T allele (in 11 cases, two alleles and in 35 cases, just one allele of 5T was detected). In 21 patients, no CFTR and 5T mutations were found (19.81%). 5T/M470 genotype was found in 19 patients, 5T/V470 was found in 3 and 5T with heterozygote form of M470V was found in 24 CBAVD patients. In CBAVD patients, 28 F508del carriers were identified. Most of our patients with CBAVD have mutations in the CFTR gene. The combination of the 5T allele in one copy of the CFTR gene with a CF mutation in the other copy is the most common cause of CBAVD in Iran. The 5T allele mutation has a wide range of clinical presentations and revealed a high frequency, occurring in patients with CBAVD or moderate forms of CF and infertile men.     

A haplotype-based molecular analysis of CFTR mutations associated with respiratory and pancreatic diseases

Aberrant membrane transport caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene is associated with a wide spectrum of respiratory and digestive diseases as well as cystic fibrosis. Using a gene scanning method, we found 11 polymorphisms and mutations of the CFTR gene in the Korean population. Individual variants at these sites were analyzed by conventional DNA screening in 117 control and 75 patients having bronchiectasis or chronic pancreatitis. In a haplotype determination based on a Bayesian algorithm, 15 haplotypes were assembled in the 192 individuals tested. Several haplotypes, especially with Q1352H, IVS8 T5, and E217G, were found to have disease associations in a case-control study. Notably, a common polymorphism of M470V appears to affect the intensity of the disease association. Among the two haplotypes having IVS8 T5, the T5-V470 haplotype showed higher disease association than the T5-M470 haplotype. In addition, a Q1352H mutation found in a V470 background showed the strongest disease association. The physiological significances of the identified mutations were rigorously analyzed. Non-synonymous E217G and Q1352H mutations in the M470 background caused a 60-80% reduction in CFTR-dependent Cl(-) currents and HCO3(-) -transport activities. Surprisingly, the additional M470V polymorphic variant with the Q1352H mutation completely abolished CFTR-dependent anion transport activities. These findings provide the first evidence on the importance of CFTR mutations in the Asian population. Importantly, the results also reveal that interactions between multiple genetic variants in cis affect the final function of the gene products.     

Molecular analysis of the cystic fibrosis gene reveals a high frequency of the intron 8 splice variant 5T in Egyptian males with congenital bilateral absence of the vas deferens

It has previously been shown that defects in the cystic fibrosis transmembrane conductance regulator (CFTR) gene are largely responsible for the condition of congenital bilateral absence of the vas deferens (CBAVD), without associated renal abnormalities, in Caucasian populations. To assess the involvement of the CFTR in CBAVD in a population with presumed low cystic fibrosis (CF) frequency, we have analysed 20 CBAVD males from Egypt for the presence of 12 common Caucasian CFTR mutations and the intron 8 5T splice variant, IVS-5T, known to be a major cause of CBAVD in Caucasian patients. In 16 of the males without associated renal abnormalities only one deltaF508 carrier was identified, but an exceptionally high frequency of the IVS-5T variant was found (14 of 32 alleles or 43.7%), confirming that this variant is involved in many cases of CBAVD, even in populations where CF is rare. CFTR mutations or the IVS-5T variant were found neither in the remaining four patients with associated renal abnormalities nor in the spouses of the 20 CBAVD patients. However, one patient was homozygous for a leucine to proline substitution at amino acid position 541 (L541P) of the CFTR. It is as yet not clear whether this change is involved in CBAVD in this male.     

The susceptibility of T5-TG12 of theCFTR gene in chronic bronchitis occurrence in a Chinese population in Jiangsu province,China

Mutations in the cystic fibrosis transmembrane conductance regulator(CFTR) gene have been implicated in the onset of cystic fibrosis and other clinical respiratory disorders.In the present study,we investigated the role of CFTR variations,poly-T,TG-repeats,and M470V in susceptibility to bronchial asthma and chronic bronchitis in a Chinese population in Jiangsu province,China.A total of 72 bronchial asthma patients,68 chronic bronchitis patients,and 117 healthy subjects were included in this study.The Tn-TGm haplotype was sequenced and the CFTR variant M470V was detected using restriction fragment length polymorphism(RFLP).We found that the frequency of T5-TG12-V470 in chronic bronchitis patients was 0.07%,which was notably higher than that in healthy subjects(0.01%) and bronchial asthma patients(0.04%).Thus,the presence of the T5-TG12 haplotype of the CFTR gene is likely to play a role in the development and progression of respiratory conditions,such as chronic bronchitis.     

Bronchiectasis in adult patients: an expression of heterozygosity for CFTR gene mutations?

While all patients with cystic fibrosis (CF) have mutations in both CFTR alleles, often only one CFTR change is detected in patients with other lung disorders. The aim of this study was to investigate whether heterozygosity for CFTR mutations could be a determinant risk factor in the development of bronchiectasis in adult patients. We have performed the CFTR gene analysis in a cohort of 55 bronchiectasis adult patients with unknown etiology. The 5T variant (TG)m and the M470V polymorphisms were also analyzed. A general population in which the same molecular analysis was previously performed was used as the control group. The mutational spectrum of patients was also compared with that found in our CF population. CFTR mutations/variants were found in 20 patients (36%), 14 with only one mutant gene (25%). All six patients colonized by Staphylococcus aureus presented with at least one CFTR change (p = 0.001). No statistical significance was observed between patients with and without mutations for other clinical features. The 5T variant was found in four patients. Additionally, 90% of patients with mutations had the more functional M470 allele (p < 0.001). These results suggest the involvement of the CFTR gene in bronchiectasis of unknown etiology in adult patients.     

Mutation spectrum of the CFTR gene in Taiwanese patients with congenital bilateral absence of the vas deferens

BACKGROUND: Clinically affected cystic fibrosis (CF) patients present a spectrum of genital phenotypes ranging from normal fertility to moderately impaired spermatogenesis and congenital bilateral absence of vas deferens (CBAVD). Little is known about the CF incidence in the Taiwanese population. It has been shown that the CBAVD in men without clinical evidence of CF is associated with a high incidence of mutated CFTR (cystic fibrosis transmembrane conductance regulator) alleles. In order to understand the involvement of the CFTR gene in the aetiology of Asian/Taiwanese male infertility, we screened the entirety of the CFTR gene in 36 infertile males with CBAVD. METHODS: Temporal temperature gradient gel electrophoresis (TTGE) followed by direct DNA sequencing was used. RESULTS: Five mutations, p.V201M, p.N287K, c.-8G > C (125G > C), p.M469I and p.S895N, were found in five of the patients. p.N287K occurred in the first transmembrane-spanning domain, p.M469I in the first ATP-binding domain and p.S895N in the second transmembrane-spanning domain, were novel. In addition, seven homozygous and seven heterozygous 5T alleles in the intron 8 poly(T) tract were found. The overall frequency of CFTR mutant alleles in Taiwanese CBAVD males was 26 out of 72 = 36%. This finding was lower than the published frequency of CFTR mutations in other ethnic CBAVD patients (ranging from 50 to 74%). The frequency of p.M470V in Taiwanese CBAVD patients is not significantly different from that in the general population (P = 0.12). CONCLUSIONS: The results of this study add to the short list of Taiwanese/Asian CFTR mutations. Unlike Caucasian patients, the CFTR mutations cannot account for the majority of Taiwanese CBAVD. This is consistent with the low incidence of CF in the Asian/Taiwanese population. Furthermore, the mutation spectrum of CFTR in CBAVD patients does not overlap with the Caucasian CFTR mutation spectrum.     

Screening of mutations in the CFTR gene in 1195 couples entering assisted reproduction technique programs

Genetic testing of the cystic fibrosis transmembrane conductance (CFTR) gene is currently performed in couples undergoing assisted reproduction techniques (ART), because of the high prevalence of healthy carriers in the population and the pathogenic relationship with congenital bilateral absence of vas deferens (CBAVD). However, discordant data have been reported concerning the usefulness of this genetic test in couples with no family history of cystic fibrosis (CF). In this study, we report the results of CFTR molecular screening in 1195 couples entering ART. Genetic testing was initially carried out in a single partner of each couple. CFTR mutations were detected in 55 subjects (4.6%), a percentage that overlaps with the one reported in the general population. However, significantly higher frequencies of were found in CBAVD individuals (37.5%) and in males with nonobstructive azoospermia (6.6%). The 5T allele was found in 78 patients (6.5%). This figure was again significantly different in males with nonobstructive-azoospermia (9.9%) and in those with CBAVD (100%). All together, 139 subjects (11.6%) had either a CFTR mutation or the 5T allele. Subsequent molecular analysis of their partners disclosed a CFTR mutation or 5T allele in nine cases (6.5%). However, none of these couples had CFTR alterations in both members, a CFTR mutation being invariably present in one partner and the 5T allele in the other. In order to improve genetic counselling of these couples, the TG-M470V-5T association was analyzed, and a statistically significant relationship between 12TG-V470 and CBAVD was detected.     

Genetic findings in congenital bilateral aplasia of vas deferens patients and identification of six novel mutatations. Mutations in brief no. 138. Online

Congential bilateral aplasia of vas deferens (CBAVD), a form of male sterility, has been suggested to represent a "genital" form of cystic fibrosis (CF), as mutations in the CFTR gene have been identified in most patients with this condition. Interestingly, the 5T allele in intron 8 appeared to be the most frequent mutation associated with CBAVD. However, the molecular basis of CBAVD is not completely understood. We have analysed the complete coding and flanking CFTR sequences by PCR-DGGE in 64 men with CBAVD from southern France with the aim to list any sequence alteration. Fourty-two of the 64 patients (65.6%) had mutations on both copies of the CFTR gene, including one patient with two mutations in the same copy (DF508 + A1067T). The 5T allele was present in 21/64 cases (33%). Six of the 28 different mutations identified in this study had never been described previously, and appeared to be specific to CBAVD (P111L, M244K, A1364V, G544V, 2896insAG,-33G->A).     

Missense mutations in the cystic fibrosis gene in adult patients with asthma

Asthma is a complex genetic disorder that affects 5% of adults and 10% of children worldwide. The complete characterization of the cystic fibrosis transmembrane conductance regulator (CFTR) gene identified missense mutations in 15% of 144 unrelated adult patients with asthma, but in none of 41 subjects from the general population. The four more common mutations were analyzed in an extended sample consisting of 184 individuals from the general population and did not show a significant difference in frequency. The hyperfunctional CFTR M470 allele was detected in 90% of patients with CFTR missense mutations, but in 63% of subjects from the general population and 63% of asthma patients without CFTR mutations. None of the patients with missense mutations had the 5T allele of intron 8 of CFTR, responsible for low CFTR levels, while it was detected in 8% of asthma patients without CFTR mutations and in 9% of subjects from the general population. These findings suggest a putative role for a combination of CFTR missense mutations, including the M470 allele, in the genetic variability of asthma.     

Genetic findings in congenital bilateral aplasia of vas deferens patients and identification of six novel mutations

Congenital bilateral aplasia of vas deferens (CBAVD), a form of male sterility, has been suggested to represent a "genital" form of cystic fibrosis (CF), as mutations in the CFTR gene have been identified in most patients with this condition. Interestingly, the 5T allele in intron 8 appeared to be the most frequent mutation associated with CBAVD. However, the molecular basis of CBAVD is not completely understood. We have analysed the complete coding and flanking CFTR sequences by PCR-DGGE in 64 men with CBAVD from southern France with the aim to list any sequence alteration. Fourty-two of the 64 patients (65.6%) had mutations on both copies of the CFTR gene, including one patient with two mutations in the same copy (DF508 + A1067T). The 5T allele was present in 21/64 cases (33%). Six of the 28 different mutations identified in this study had never been described previously, and appeared to be specific to CBAVD (P111L, M244K, A1364V, G544V, 2896insAG, -33G→A). Hum Mutat 11:480, 1998. © 1998 Wiley-Liss, Inc.     

Contribution of the CFTR gene, the pancreatic secretory trypsin inhibitor gene (SPINK1) and the cationic trypsinogen gene (PRSS1) to the etiology of recurrent pancreatitis

Acute recurrent/chronic pancreatitis (CP) is a complex multigenic disease. This is a case-control study consisting of 25 Greek patients with CP and a control population of 236 healthy Greek subjects. The whole coding area and neighboring intronic regions of the three genes were screened. Seventeen of 25 patients (68%) had mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene: nine compound heterozygotes with either mild or severe mutations and eight heterozygotes. Four patients (16%) carried CFTR-modulating haplotypes V470-TG11-T5 and V470-TG12-T7. All were negative for PRSS1 gene mutations, while variants c.486C/T and c.738C/T were found in nine patients each, three homozygotes for the minor alleles. Two carried SPINK1 gene mutation p.N34S, one being transheterozygote with CFTR mutation p.F1052V. The promoter variant -253T>C was found in four individuals (one homozygous for the minor allele), all four being transheterozygotes with mutations in the CFTR gene as well. Finally two carried c.272C/T in the 3' untranslated region, one being a p.N34S carrier as well. In total, 80% (20/25) of patients had a molecular defect in one or both of the CFTR and SPINK1 genes, suggesting that mutations/variants in the CFTR plus or minus mutations in the SPINK1, but not the PRSS1 gene, may confer a high risk for recurrent pancreatitis.     

Two novel missense and one novel nonsense CFTR mutations in Iranian males with congenital bilateral absence of the vas deferens

Congenital bilateral absence of the vas deferens (CBAVD) is a frequent cause of obstructive azoospermia. Nearly 75% of men with CBAVD have at least one detectable common cystic fibrosis (CF) transmembrane conductance regulator (CFTR) mutation. To study the involvement of CFTR mutations in the Iranian population with presumed low CF frequency, we analysed 112 Iranian CBAVD males. Three Iranian CBAVD males with no clinical CF phenotype indicated by a normal karyotype, normal pancreatic function and sweat chloride concentration and no Y chromosome microdeletions were studied for CFTR mutations, IVS8-5T mutations and M470V exon 10 missense polymorphism. The entire coding sequence of each gene was analysed using a combination of the denaturing gradient-gel electrophoresis or by single-strand conformation analysis and direct DNA sequencing. Also, 52 fertile males were tested as controls to rule out polymorphism. This approach allowed us to detect one novel nonsense mutation (K536X) in the nucleotide-binding domain 1 (NBD1) region and two novel missense mutations (Y122H and T338A) in the M2 and M6 regions of CFTR gene in our studied population, which were not reported previously. Also, the conservation of changed nucleotide and amino acid in mutated regions was analysed by aligning with nine different species. K536X nonsense mutation (transversion) was found in the first NBD (NBF1), which plays an important regulatory role in CFTR function. It was, therefore, considered as a severe allele responsible for elevated sweat chloride levels and obstructive azoospermia. Because Y122H and T338A mutations were compound heterozygote with the IVS8-5T, it is difficult to judge the severity of these mutations and their role in the CBAVD phenotype.     

Identification and characterization of CFTR gene mutations in Indian CF patients

Cystic fibrosis (CF) is an autosomal recessive disease caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. This study was performed on Indian CF patients (n = 50) to investigate the spectrum of mutations in the CFTR gene and their association with intragenic and extragenic marker haplotypes. We report identification of 14 previously known and eight novel mutations, namely 3986-3987delC, 876-6del4, 1792InsA, L69H, S158N, Q493L, I530L and E1329Q. The frequency of delta F508 was found to be 27%. Absolute linkage between delta F508 and the KM.19-GATT-TUB9-M470V-T854T haplotype (2-2-1-1-1) predicts a relatively recent appearance of delta F508 in Indian CF patients. Low frequency of delta F508 mutation and detection of eight novel and thirteen rare mutations reflect a heterogeneous spectrum of mutations in Indian CF patients. Failure to detect mutations in 34% of alleles indicates the possible presence of gross deletions involving one or more exons or may indicate the location of the molecular defects in either the noncoding parts of the gene or in the promoter region, which warrants analysis of those regions.     

Cystic fibrosis transmembrane conductance regulator gene screening and clinical correlation in Taiwanese males with congenital bilateral absence of the vas deferens

BACKGROUND: In Taiwan, an area with a very low incidence of cystic fibrosis (CF), we first screened for the most common mutations of the cystic fibrosis transmembrane conductance regulator (CFTR) gene and looked for clinical correlations in 27 patients with clinically diagnosed congenital bilateral absence of the vas deferens (CBAVD). METHODS AND RESULTS: The clinical results showed that none of the 27 patients had CF symptoms. We did not detect any definite renal anomaly ultrasonographically. Mutation analysis was carried out on these 27 cases and 46 normal fertile males as controls. No mutations of Delta F508 or R117H were identified in any of the samples analysed. In the screening of IVS8-poly T, five of the 27 CBAVD patients showed the homozygous genotype for 5T/5T, 14 showed the heterozygous genotype for 5T/7T and eight showed the homozygous genotype for 7T/7T. The frequency of 5T alleles was 44.4%, which was significantly higher than in the 46 normal fertile males, for which there was a 5T frequency of 5.4%. CONCLUSIONS: The absence of major mutations of CFTR genes could be related to the much lower CF incidence in Taiwan. Further investigations into differences in the mutation spectrum of other CFTR genes are needed for a better understanding of the development of Taiwanese-Oriental CBAVD.     

Haplotype block structure study of the CFTR gene. Most variants are associated with the M470 allele in several European populations

An average of about 1700 CFTR (cystic fibrosis transmembrane conductance regulator) alleles from normal individuals from different European populations were extensively screened for DNA sequence variation. A total of 80 variants were observed: 61 coding SNSs (results already published), 13 noncoding SNSs, three STRs, two short deletions, and one nucleotide insertion. Eight DNA variants were classified as non-CF causing due to their high frequency of occurrence. Through this survey the CFTR has become the most exhaustively studied gene for its coding sequence variability and, though to a lesser extent, for its noncoding sequence variability as well. Interestingly, most variation was associated with the M470 allele, while the V470 allele showed an 'extended haplotype homozygosity' (EHH). These findings make us suggest a role for selection acting either on the M470V itself or through an hitchhiking mechanism involving a second site. The possible ancient origin of the V allele in an 'out of Africa' time frame is discussed.     

Frequency of the ΔF508 and exon 11 mutations in Norwegian cystic fibrosis patients

Eiklid K, Tranebjærg L, Eiken HG, Pedersen JC, Michalsen H, Fluge G, Schwartz M, Nilsen BR, Bolle R, Skyberg D, Boman H, Berg K. Frequency of the ΔF508 and exon 11 mutations in Norwegian cystic fibrosis patients.
Clin Genet 1993: 44: 12–14. © Munksgaard, 1993
We have searched for the ΔF508 mutation in 77 Norwegian cystic fibrosis patients. Of the 154 chromosomes tested, 93 (60%) carried the ΔF508 mutation. Haplotypes at the D7S23 locus (KM19 and XV2C markers) were determined. Of 81 chromosomes with the F508 mutation, the B haplotype was found on 77. We found three patients with the G551D and one patient with the R553X mutation in exon 11 of the CFTR locus.