Cystic fibrosis in a low-incidence population: two major mutations in Finland

The incidence of cystic fibrosis (CF) in Finland, 125 000 newborn, is one of the lowest in Caucasian populations. The F508 mutation accounts for 18/40 (45%) of CF chromosomes in Finland. Other mutations were therefore sought among the remaining 55%. Twelve out of 40 chromosomes (30%) were found to carry 394delTT, whereas G542X and 3732delA were each detected in one chromosome. Eight mutations remained unidentified using a testing panel for 26 mutations. Mutation 394delTT was associated exclusively with haplotype 23-36-13. Five unknown mutations were associated with different haplotypes for microsatellite markers, whereas three shared the same haplotype. Most F508 mutations and all unidentified mutations originated from regions of old and dense settlement in the coastal regions, whereas 394delTT was geographically clustered and enriched in a rural location, consistent with a local founder effect. The remote location of Finland and her population history give a plausible explanation for the rarity of CF in Finland.     

Analysis of the spectra of mutations and polymorphic loci of cystic fibrosis transmembrane conductance regulator in the population of Bashkortostan

The spectra of mutations and polymorphic loci of the gene of cystic fibrosis transmembrane conductance regulator (CFTR) was studied in 60 cystic fibrosis (CF) families from Bashkortostan. Mutations delF508, 394delTT, CFTRdele2,3(21 kb), R334W, and S1196X (33.3, 3.3, 1.7, 0.8, and 0.8%, respectively) were identified. The frequencies of tandem tetranucleotide repeat (TTR) alleles were determined for locus IVS6a-GATT of intron 6 of the CFTR gene and two extragenic loci flanking the CFTR gene, D7S23 and MET (probes CS.7 and MetH) in mutant and normal chromosomes. Allelic and haplotypic associations of these loci with the mutations found were estimated. An absolute linkage between the 6TTR allele of locus IVS6a-GATT and the delF508 mutation was ascertained. A considerable linkage disequilibrium between the delF508 mutation and the C2 allele of locus D7S23 and between this mutation and the A1 allele of locus MET was found. Most of the other mutant chromosomes carried marker alleles 7TTR, C1, and A2. It was demonstrated that 67% of CF chromosomes carrying delF508 had haplotype 6-2-1 for loci IVS6a-GATT/D7S23/MET, respectively. The frequency distribution of haplotypes in CF chromosomes without delF508 had a high variance and did not differ significantly from the distribution in normal chromosomes (chi 2 = 9.415; p > 0.05).     

Spectrum of cystic fibrosis mutations in Serbia and Montenegro and strategy for prenatal diagnosis

We have screened 175 patients for molecular defects in the cystic fibrosis transmembrane conductance regulator (CFTR) gene using nondenaturing polyacrylamide gel electrophoresis (PAGE), denaturing gradient gel electrophoresis (DGGE), and sequencing. Six different mutations (F508del, G542X, 621+1G --> T, 2789+5G --> A, R1070Q, and S466X) accounted for 79.71% of CF alleles, with the F508del mutation showing a frequency of 72.28%. Another 12 mutations (R334W, 2184insA, I507del, 1525-1G --> A, E585X, R75X, M1I, 457TAT --> G, 574delA, 2723delTT, A120T, and 2907delTT) covered an additional 3.36%. A novel mutation (2723delTT) was found in one CF patient (F508del/2723delTT). Thus, a total of 18 mutations cover 82.57% of CF alleles. During our study, 72% of families at risk for having a CF child were found to be fully informative for prenatal diagnosis. Prenatal diagnosis was performed on 56 families; 76 analyses resulting in 16 affected, 38 carriers, and 22 healthy fetuses. These results imply that the molecular basis of CF in Serbia and Montenegro is highly heterogeneous, as is observed in other eastern and southern European populations. Because we detected more then 80% of CFTR alleles, results could be used for planning future screening and appropriate genetic counseling programs in our country.     

The mutation spectrum of the CFTR gene in mucoviscidosis patients from Bashkortostan

Mutations of CFTR were studied in patients with cystic fibrosis (CF) from Bashkortostan. In total, 15 mutations were observed and 51% of all mutant alleles identified. The most diagnostically significant mutations were delF508 (33.8%), 394delTT (3.52%), CFTRdele2.3(21 kb) (1.41%), R334W (1.41%), 3849+ 10 kbC-->T (1.41%), and N1303K (1.41%). Mutations G542X, 2184insA, S1196X, and W1282X were each found in less than 1% patients. Five new mutations and two neutral substitutions were revealed. These were I488M (exon 10), 1811 + 12A-->C (intron 11), T663S (exon 13), I1226R (exon 19), 4005 + 9A-->C (intron 20), 2097A-->C (A655A, exon 13), and 3996G-->C (V1288V, exon 20). Bashkortostan was shown to differ in CFTR mutation spectrum from other regions of Russia. The results will allow direct DNA diagnostics of CF in far more families. Molecular screening of probands' relatives will contribute to identification and medical genetic counseling of heterozygous carriers, which is essential for CF prevention.     

Cystic fibrosis as a cause of infertility

Cystic fibrosis (CF) is one of the autosomal recessive diseases, caused by mutations in a gene known as cystic fibrosis transmembrane regulator (CFTR). The majority of adult males with CF (99%) is characterized by congenital bilateral absence of vas deferens (CBAVD). CBAVD is encountered in 1-2% of infertile males without CF. Females with CF are found to be less fertile than normal healthy women. In females with CF, delayed puberty and amenorrhoea are common due to malnutrition. CFTR mutations are also associated with congenital absence of the uterus and vagina (CAUV). The National Institutes of Health recommend genetic counseling for any couple seeking assisted reproductive techniques with a CF male or obstructive azoospermia which is positive for a CF mutation.     

A 3′ splice site consensus sequence mutation in the cystic fibrosis gene

Summary In the cystic fibrosis (CF) gene, recently cloned, a three base pair deletion (ΔF508) has been identified in a majority of CF patients. This deletion has been found in 80% of CF chromosomes in families from north west Brittany. In order to identify new mutations we have selected 43 chromosomes negative for the three base pair deletion from these families and directly sequenced exon 11 after DNA amplification by the polymerase chain reaction. We have detected a base change (G→A) at the 3′ end of the consensus sequence of intron ten (namely 1717-1). This mutation destroys a splice site in the cystic fibrosis gene which probably produces a mutant allele. This single nucleotide mutation has been reported on two other CF chromosomes.     

Analysis of the Spectra of Mutations and Polymorphic Loci of Cystic Fibrosis Transmembrane Conductance Regulator in the Population of Bashkortostan

The spectra of mutations and polymorphic loci of the gene of cystic fibrosis transmembrane conductance regulator (CFTR) was studied in 60 cystic fibrosis (CF) families from Bashkortostan. Mutations delF508, 394delTT, CFTRdele2,3(21 kb), R334W, and S1196X (33.3, 3.3, 1.7, 0.8, and 0.8%, respectively) were identified. The frequencies of tandem tetranucleotide repeat (TTR) alleles were determined for locus IVS6a-GATT of intron 6 of the CFTR gene and two extragenic loci flanking the CFTR gene, D7S23and MET(probes CS.7 and MetH) in mutant and normal chromosomes. Allelic and haplotypic associations of these loci with the mutations found were estimated. An absolute linkage between the 6TTR allele of locus IVS6a-GATT and the delF508 mutation was ascertained. A considerable linkage disequilibrium between thedelF508mutation and the C2 allele of locus D7S23and between this mutation and the A1 allele of locus MET was found. Most of the other mutant chromosomes carried marker alleles 7TTR, C1, and A2. It was demonstrated that 67% of CF chromosomes carrying delF508 had haplotype 6–2–1 for loci IVS6a-GATT/D7S23/MET, respectively. The frequency distribution of haplotypes in CF chromosomes without delF508had a high variance and did not differ significantly from the distribution in normal chromosomes (² = 9.415; p > 0.05)).     

Analysis of the CFTR gene in Turkish cystic fibrosis patients: identification of three novel mutations (3172delAC, P1013L and M1028I)

In order to determine the spectrum of cystic fibrosis (CF) mutations in the Turkish population, a complete coding region of the cystic fibrosis transmembrane conductance regulator (CFTR) gene including exon-intron boundaries, on 122 unrelated CF chromosomes from 73 Turkish CF families was analysed by denaturing gradient gel electrophoresis and multiplex heteroduplex analysis on MDE gel matrix. In addition to 15 previously reported mutations and 12 polymorphisms, three novel mutations, namely 3172delAC, P1013L and M1028I, were detected. ΔF508 was found to be present on 18.8% of CF chromosomes. The second most common mutation was 1677delTA, with a frequency of 7.3%, followed by G542X and 2183AA→G mutations, with frequencies of 4.9%. These four most common mutations in Turkish CF population account for approximately 36% of mutations. This study could only detect 52.5% of disease-causing mutations in this population; 47.5% of CF alleles remain to be identified, reflecting the high molecular heterogeneity of the Turkish population. Received: 16 June 1997 / Accepted: 18 September 1997     

The haplotype distribution of the ΔF508 mutation in cystic fibrosis families in Scotland

Summary The gene defective in cystic fibrosis (CF) has recently been isolated and the major mutation identified. The haplotype distribution of this mutation (ΔF508) has been determined for 215 CF chromosomes in the Scottish population. ΔF508 represents 73% of all CF mutations in this group. There remains considerable linkage disequilibrium between XV2c and KM19 and other mutations in the CF gene.     

Genetic comparisons of patients with cystic fibrosis with or without meconium ileus. Clinical Centers of the French CF Registry.

Cystic fibrosis (CF) is an autosomal disorder caused by mutations in the cystic fibrosis transmembrane conductance regulator gene (CFTR). Neonatal meconium ileus (MI) occurs in 10-20 percent of newborns with CF. The purpose of this study was to determine the allelic frequencies of the CF mutation in French patients with and without MI and the incidence of MI in 7 homozygotes or compound heterozygotes for mutation of the CFTR gene. Our study confirms the positive association between delta F508, the most frequent CF mutation, G542X mutation and MI and a negative association with G551D.     

Genotype-phenotype correlation in cystic fibrosis patients bearing [H939R;H949L] allele

Cystic fibrosis (CF) is caused by CFTR (cystic fibrosis transmembrane conductance regulator) gene mutations. We ascertained five patients with a novel complex CFTR allele, with two mutations, H939R and H949L, inherited in cis in the same exon of CFTR gene, and one different mutation per patient inherited in trans in a wide population of 289 Caucasian CF subjects from South Italy. The genotype-phenotype relationship in patients bearing this complex allele was investigated. The two associated mutations were related to classical severe CF phenotypes.     

CF2603/4delT,a new frameshift mutation in exon 13 of the cystic fibrosis transmembrane conductance regulator (CFTR) gene

By using temperature gradient gel electrophoresis to screen for mutations in cystic fibrosis (CF) patients, we have found a new mutation in the CF transmembrane conductance regulator gene. It is a frameshift mutation named CF2603/4delT located at the 3-end of exon 13. A thymidine at position 2603 or 2604 is lost. The mutation eliminates an MseI site and, therefore, can be screened by restriction enzyme analysis.     

CA/GT microsatellite alleles within the cystic fibrosis transmembrane conductance regulator (CFTR) gene are not generated by unequal crossingover.

The gene responsible for cystic fibrosis (CF) has recently been identified, and a three-nucleotide deletion (delta F508 mutation) that results in the loss of a phenylalanine residue in the first putative ATP-binding domain of the predicted protein (CF transmembrane conductance regulator, CFTR) has been found to be the major CF mutation. Although several other mutations have been identified in the CFTR gene, most of them are very rare, making their application to genetic diagnosis difficult. While characterizing the genomic region encompassing the CF locus, we have identified three CA/GT blocks that flank exon 9 of the CF gene. One of the CA/GT blocks exhibits a highly informative variable number of dinucleotide repeats (VNDR) polymorphism. This intragenic VNDR microsatellite should, by itself, provide full information for genetic analysis in approximately 80% of CF families and will help elucidate the associations between DNA polymorphism haplotypes and specific gene mutations. Haplotype analyses of CF chromosomes with and without the delta F508 mutation suggest that the different alleles are generated by slipped-strand mispairing within the dinucleotide repeat during DNA replication, rather than by unequal crossingover within a recombination hot spot.     

Detection of 98.5% of the mutations in 200 Belgian cystic fibrosis alleles by reverse dot-blot and sequencing of the complete coding region and exon/intron junctions of the CFTR gene

We have previously shown that about 85% of the mutationsin 194 Belgian cystic fibrosis alleles could be detected by a reverse dot-blot assay (7). In the present study, 50 Belgian chromosomes were analyzed for mutations in the cystic fibrosis transmembrane conductance regulator gene by means of direct solid phase automatic sequencing of PCR products of individual exons. Twenty-six disease mutations and 14 polymorphisms were found. Twelve of these mutations and 3 polymorphisms were not described before. With the exception of one mutant allele carrying two mutations, these mutations were the only mutations found in the complete coding region and their exon/intron boundaries. The total sensitivity of mutant CF alleles that could be identified was 98.5%. Given the heterogeneity of these mutations, most of them very rare, CFTR mutation screening still remains rather complex in our population, and population screening, whether desirable or not, does not appear to be technically feasible with the methods currently available.     

The search for south European cystic fibrosis mutations: identification of two new mutations, four variants, and intronic sequences

The major mutation in the cystic fibrosis (CF) gene is a 3-bp deletion (delta F508) in exon 10. About 50% of the CF chromosomes in Southern Europe carry this mutation, while other previously described mutations account for less than 4%. To identify other common mutations in CF patients from the Mediterranean area, we have sequenced, exon by exon, 16 chromosomes that did not show the delta F508 deletion from a selected panel of eight unrelated CF patients. We describe here one missense and one nonsense mutation, and four sequence polymorphisms. We have also found two previously reported mutations in three chromosomes. Overall, these mutations may account for about 20% of CF alleles in the Italian and Spanish populations. No other mutations were detected in 10 out of 16 CF chromosomes after analyzing about 90% of the coding region of the CF gene, and 39 out of 54 intron/exon boundaries. Therefore, about 26% of CF mutations remain to be identified. In addition we provide the intron/exon boundary sequences for exons 4 to 9. These results together with previously reported linkage data suggest that in the Mediterranean populations further mutations may lie in the promoter region, or in intron sequences not yet analyzed.     

The frequency of mutations in exon 11 of the CF gene in Polish cystic fibrosis patients.

Results of mutation analysis in exon 11 of the CF gene have been presented. Using the SSCP technique 18 mutations (of four different types) were detected in cystic fibrosis patients of Polish origin. Thus, we were able to detect in exon 11 about 10% of all CF mutations occurring in the affected population examined.     

First report of c. 1499G>C mutation in a 6-month-child with cystic fibrosis

So far, more than 1800 mutations identified in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. In this case report, we presented first report of c. 1499G>C mutation in a 6-month-old girl with cystic fibrosis (CF) diagnosis. A 6-month-old girl with weakness and meconium Ileus referred to the pediatric clinic in Ilam, in the west of Iran. Patient''s skin was dark and suffered from bronchiectasis. The sweat test was performed, and the concentration of chloride and sodium in patient''s sweat was 130-135 mmol/L and 125-128 mmol/L, respectively. The exon 10 mutation analysis of a CF patient was performed. CFTR mutation analysis revealed the identification of 2 mutations in patient, the mutations were p.F508del (ΔF508) and c. 1499G>C (cd500), respectively. The mutation c. 1499G>C (cd500) were found for the first time in the world. Assessing this mutation in future study and genetic investigation is recommended.     

Polymorphic markers suggest a gene flow of CFTR gene from Sub-Saharan/Arabian and Mediterranean to Brazilian Population

The analysis of 2 diallelic loci (M470V and T854T) and a microsatellite IVS8(T)n of the cystic fibrosis transmembrane conductance regulator (CFTR) gene has shown different haplotype distribution in Brazilian cystic fibrosis (CF) chromosomes carrying different CF mutations. The DeltaF508 mutation was in absolute linkage disequilibrium with 1-1 haplotype (M470V-T854T). Most of DeltaF508 chromosomes (84%) were found to carry the IVS8-9T. The most frequent haplotypes IVS8-7T and 2-1 (M470V-T854T) were found associated with Non-DeltaF508 mutations. Although there is a remarkable linkage disequilibrium between these markers with CFTR locus, the mutations R334W (7T-1-2 and 7T-2-1) and the 3120 + 1G --> A (7T-1-2 and 9T-1-2) are associated with two different haplotypes probably introduced in the Brazilian population by migration. These findings suggest that recombination events from the original haplotype and gene flow among different ethnic groups (sub-Saharan and Mediterranean) might have resulted in CF mutations associated with different haplotypes by independent introductions.     

A new mutation, 3905insT, accounts for 4.8% of 1173 CF chromosomes in Switzerland and causes a severe phenotype

We have analysed 1173 cystic fibrosis (CF) chromosomes from Switzerland for eight mutations in the CF transmembrane conductance regulator (CFTR) gene. This permitted the identification of 88.5% of all mutations present. A novel insertion mutation in exon 20 of the CFTR gene, 3905insT, was discovered. This mutation accounted for 4.8% of CFTR gene mutations in Switzerland and has since been identified in other populations of probable Swiss descent. It is associated with a highly variable clinical phenotype but always with pancreatic insufficiency. Haplotype analysis with three intragenic microsatellites in the CFTR gene showed that the mutation is associated with a haplotype rarely identified on other CFTR alleles and, therefore, that the frequency of the mutation in Switzerland is explained by a founder effect of a relatively recent mutation event. Received: 17 February 1997 / Accepted: 26 March 1977