The occurrence of various non-ΔF508 CFTR gene mutations among Hungarian cystic fibrosis patients

Summary Cystic fibrosis (CF) is an autosomal recessive disease caused by different mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. The frequency of the major mutation (F508) in the Hungarian population is 64%. To identify other common mutations in CF families from Hungary, 30 nonF508 CF chromosomes were analyzed for selected mutations in exon 11 (G551D, R553X, G542X), intron 4 (621+1GT), intron 10 (1717–1GA), exon 20 (W1282X), and in exon 21 (N1303K) of the CFTR gene. In 6 of the 30 non-F508 CF chromosomes the following mutations were detected: R553X, G542X, 1717–1GA, W1282X, and N1303K. After analysis of the above eight mutations, 30% of CF chromosomes are as yet undefined and further analysis is planned.     

The Mutation Spectrum of the CFTR Gene in Cystic Fibrosis 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(21kb) (1.41%), R334W (1.41%), 3849 + 10kbC 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 the 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.     

A novel donor splice site in intron 11 of the CFTR gene, created by mutation 1811+1.6kbA-->G, produces a new exon: high frequency in Spanish cystic fibrosis chromosomes and association with severe phenotype.

mRNA analysis of the cystic fibrosis transmembrane regulator (CFTR) gene in tissues of cystic fibrosis (CF) patients has allowed us to detect a cryptic exon. The new exon involves 49 base pairs between exons 11 and 12 and is due to a point mutation (1811+1.6kbA-->G) that creates a new donor splice site in intron 11. Semiquantitative mRNA analysis showed that 1811+1.6kbA-->G-mRNA was 5-10-fold less abundant than delta F508 mRNA. Mutation 1811+1.6kbA-->G was found in 21 Spanish and 1 German CF chromosomes, making it the fourth-most-frequent mutation (2%) in the Spanish population. Individuals with genotype delta F508/1811+1.6kbA-->G have only 1%-3% of normal CFTR mRNA. This loss of 97% of normal CFTR mRNA must be responsible for the pancreatic insufficiency and for the severe CF phenotype in these patients.     

Molecular analysis in Brazilian cystic fibrosis patients reveals five novel mutations

We have performed molecular genetic analyses on 160 Brazilian patients diagnosed with cystic fibrosis (CF). Screening of mutations in 320 CF chromosomes was performed through single strand conformation polymorphism (SSCP) and heteroduplex analyses assay followed by DNA sequencing of the 27 exons and exon/intron boundaries of the cystic fibrosis transmembrane conductance regulator (CFTR) gene. The frequency of CFTR variants of T-tract length of intron 8 (IVS8 Tn) was also investigated. This analysis enabled the detection of 232/320 CF mutations (72.2%) and complete genotyping of 61% of the patients. The deltaF508 mutation was found in 48.4% of the alleles. Another fifteen mutations (previously reported) were detected: G542X, R1162X, N1303K, R334W, W1282X, G58E, L206W, R553X, 621+1G-->T, V232D, 1717-1G-->A, 2347 delG, R851L, 2789+5G-->A, and W1089X. Five novel mutations were identified, V201M (exon 6a), Y275X (exon 6b), 2686 insT (exon 14a), 3171 delC (exon 17a), and 3617 delGA (exon 19). These results contribute to the molecular characterization of CF in the Brazilian population. In addition, the identification of the novel mutation Y275X allowed prenatal diagnosis in a high-risk fetus.     

Exon 9 of the CFTR gene: splice site haplotypes and cystic fibrosis mutations

The alternatively spliced exon 9 of the cystic fibrosis transmembrane conductance regulator (CFTR) gene codes for the initial part of the amino-terminal nucleotide-binding fold of CFTR. A unique feature of the acceptor splice site preceding this exon is a variable length polymorphism within the polypyrimidine tract influencing the extent of exon 9 skipping in CFTR mRNA. We investigated this repeat for its relationship to CFTR mutations and intragenic markers on 200 chromosomes from German patients with cystic fibrosis (CF). Four frequent length variations were strongly associated with the four predominant haplotypes previously defined by intragenic marker dimorphisms. One of these alleles displayed absolute linkage disequilibrium to the major CF mutation F508. Other frequent CFTR mutations were linked to one particular splice site haplotype indicating that differential exon 9 skipping contributes little to the clinical heterogeneity among CF patients with an identical mutation. We also identified a novel missense mutation (V456F) and a novel nonsense mutation (Q414X) within the coding region of exon 9. The missense mutation V456F adjacent to Walker motif A was present in a pancreas-sufficient CF patient. In contrast, the pancreas-insufficient Q414X/F508 compound heterozygote suffered from a severe form of the disease, indicating that alternative splicing of exon 9 does not overcome the deleterious effect of a stop codon within this exon.     

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.     

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)).     

Extended haplotype analysis of cystic fibrosis mutations and its implications for the selective advantage hypothesis

The major cystic fibrosis (CF) mutation, F508, is associated with one haplotype (B) determined by the two polymorphic markers, XV2C and KM19. This haplotype is rare (15%) among non-F chromosomes. Its frequency among non-F508 CF chromosomes is 50% with variation between populations. One hypothesis for the high frequency of CF haplotype B chromosomes suggests that there was a selective advantage for CF mutations on this specific background as a result of epistatic selection at other closely linked loci. Since the XV2C and KM19 markers are located 200kb 5 to the CF gene and span only 60 kb, an extended haplotype analysis was needed to test this hypothesis. Haplotypes were determined for 183 CF and 120 non-CF Israeli chromosomes at the XV2C and KM19 loci and at three intragenic polymorphic sites (GATT in intron 6A, TUB18 in intron 19, and 24M in exon 24). Among the studied chromosomes the frequency of non-F508 CF chromosomes associated with haplotype B was 70% (88% among Ashkenazi CF chromosomes). Nine mutations (F508, W1282X, G542X, N1303K, 3849+10 kb CT, Q359K/T360K, S549I, S549R, and 1717-1GA) were identified among the studied chromosomes. These mutations accounted for 96% of CF chromosomes of Ashkenazi origin. Haplotype B was associated with seven of these (F508, W1282X, G542X, N1303K, Q359K/ T360K, S549R, and 1717-1GA). The extended haplotype analysis revealed that in five of the seven mutations associated with the haplotype B, 97% of the chromosomes shared the same intragenic haplotype, 212. The variation found in 3% of the chromosomes was only in the GATT repeat. Two mutations, W1282X and 1717-1GA, were associated with a completely different intragenic haplotype, 121. The results of this study indicate that grouping of CF chromosome by haplotype analysis spanning a small extragenic region might not be sufficient. In addition, the results of the extended haplotype analysis indicate that all the studied CF chromosomes that carry the same mutation derived from the same origin. Furthermore, the results indicate that the majority of the CF mutations are associated with the same extended haplotype, supporting the selective advantage hypothesis.     

Different evolutionary pathway of B*570101 and B*5801 (B17 group) alleles based in intron sequences

Two theories about MHC allele generation have been put forward: (1) point mutation diversification and/or (2) gene conversion events. A model supporting the existence of both of these mechanisms is shown in this paper; the possible evolution of the HLA-B*570101 and HLA-B*5801 alleles (which belong to the HLA-B17 serology group) is studied. The hypothesis favoured is that gene conversion events have originated these alleles, because intron sequences are also analysed. Evolution by point mutation should only be accepted if flanking introns have also been sequenced.The nucleotide sequence data (exons and introns) reported in this paper have been sequenced in our laboratory. They are in the GenBank nucleotide sequence database and have been assigned the accession numbers: B*150101—(a) exon 1, L79939; (b) exon 2 and exon 3, L48400; (c) intron 1, L76249; (d) intron 2, L42468; B*1515—(a) exon 1, exon 2 and exon 3, L49343; (b) intron 1 and intron 2, L76254; B*1539—(a) exon 2, AF033501; (b) exon 3, AF033502; (c) intron 1, AF034961; (d) intron 2 AF034962; B*350101—(a) exon 1, exon 2 and exon 3, L63544; (b) intron 1, L79921; (c) intron 2, L57505; B*510101—(a) exon 1, L77204; (b) exon 2 and exon 3, L47985; (c) intron 1, L76245; (d) intron 2, L42469; B*520102—(a) exon 1, L77205; (b) exon 2 and exon 3, L47984; (c) intron 1, L76244; (d) intron 2, L76251; B*5301—(a) exon 1, intron 1, exon 2, intron 2 and exon 3, U90566; B*1302—(a) intron 1, exon 2, intron 2, exon 3, AF196182; B*400101/02—(a) exon 2 and exon 3, L79937; (b) intron 1, L79919; (c) intron 2, L76629; B*4101—(a) intron 1, exon 2, intron 2 and exon 3, U90560; B*4102 (a) intron 1, exon 2, intron 2 and exon 3, AF 126199; B*4501—(a) intron 1, exon 2, intron 2 and exon 3, U90562; B*570101—(a) intron 1, exon 2, intron 2 and exon 3, AF196183; B*5801—(a) intron 1, exon 2, intron 2 and exon 3, AF196184All exon sequences were officially assigned as confirmatory by the WHO Nomenclature Committee in December 2003: B*1302, B*150101, B*350101, B*400101/02, B*4101, B*510101, B*570101, B*5801, B*5301, B*4501, B*520102, B*1515, B*4102 and B*1539. This follows the agreed policy that, subject to the conditions stated in the Nomenclature Report [Marsh et al. (2002) Tissue Antigens 60:407–464], names will be assigned to new sequences as they are identified. Lists of such new names will be published in the following WHO Nomenclature Report     

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.     

Intra- and extragenic marker haplotypes of CFTR mutations in cystic fibrosis families

Summary In order to facilitate the screening for the less common mutations in the cystic fibrosis (CF) gene viz., the CF transmembrane conductance regulator gene (CFTR), marker haplotypes were determined for German nonCF (N) and CF chromosomes by polymerase chain reaction analysis of four polymorphisms upstream of the CF gene (XV-2c, KM.19, MP6-D9, J44) and six intragenic polymorphisms (GATT, TUB9, M470V, T854T, TUB18, TUB20) that span the CFTR gene from exon 6 through exon 21. Novel informative sequence variants of CFTR were detected in front of exons 10 (1525-61 A or G), 19 (3601-65 C or A), and 21 (4006-200 A or G). The CF locus exhibits strong long-range marker-marker linkage disequilibrium with breakpoints of recombination between XV-2c and KM.19, and between exons 10 and 19 of CFTR. Marker alleles of GATT-TUB9 and TUB18-TUB20 were found to be in absolute linkage disequilibrium. Four major haplotypes encompass more than 90% of German N and CF chromosomes. Fifteen CFTR mutations detected on 421 out of 500 CF chromosomes were each identified on one of these four predominant 7-marker haplotypes. Whereas all analysed F508 chromosomes carried the same KM.19-D9-J44-GATT-TUB9-M470V-T854T haplotype, another frequent mutation in Germany, R553X, was identified on two different major haplotypes. Hence, a priori haplotyping cannot exclude a particular CF mutation, but in combination with population genetic data, enables mutations to be ranked by decreasing probability.     

Nature and frequency of mutations in the argininosuccinate synthetase gene that cause classical citrullinemia

Citrullinemia is an autosomal recessive disorder caused by a genetic deficiency of argininosuccinate synthetase (ASS). So far 20 mutations in ASS mRNA have been identified in human classical citrullinemia, including 14 single base changes causing missense mutations in the coding sequence of the enzyme, 4 mutations associated with an absence of exons 5, 6, 7, or 13 in mRNA, 1 mutation with a deletion of the first 7 bases in exon 16 (which is caused by abnormal splicing), and 1 mutation with an insertion of 37 bases between the exon 15 and 16 regions in mRNA. In order to identify the abnormality in the ASS gene causing the exon 7 and 13 deletion mutations and the 37-base insertion mutation between exons 15 and 16 in mRNA, and to establish a DNA diagnostic test, we isolated and sequenced the genomic DNA surrounding each exon. The absence of exon 7 or 13 in ASS mRNA resulted from abnormal splicing caused by a single base change in the intron region: IVS-6^–2 (a transition of A to G at the second nucleotide position within the 3 splice cleavage site of intron 6) and IVS-13⁺⁵ (a transition of G to A at the fifth nucleotide position within the 5 splice cleavage site of intron 13), respectively. The IVS-6^–2 mutation resulted in the creation of an MspI restriction site. DNA diagnostic analysis of 33 Japanese alleles with classical citrullinemia showed that 19 alleles had the IVS-6^–2 mutation (over 50% of the mutated alleles in Japanese patients). It was thus confirmed that one mutation is predominant in Japan. This differs from the situation in the USA where there is far greater heterogeneity. The insertion mutation in mRNA on the other hand resulted from abnormal splicing caused by a 13-bp deletion at the splice-junction between exon 15 and intron 15. The deletion had a short direct repeat (CTCAGG) at the breakpoint junction and presumably resulted from slipped mispairing.     

Analysis of the complete coding region of the CFTR gene in a cohort of CF patients from North-Eastern Italy: identification of 90% of the mutations

A complete coding-region analysis on 225 cystic fibrosis (CF) chromosomes from a cohort that includes all the affected subjects born in two North-Eastern Italian regions over eight years was performed. In a previous study, we identified mutations on 166/225 (73.8%) CF chromosomes after screening for 62 mutations. To characterise the remaining 59 CF chromosomes, we carried out automated direct DNA sequencing (exons 9 and 13), RNA single-strand conformation polymorphism (exons 1–8 and 10–12) and denaturing gradient gel electrophoresis (exons 14a–24) of the 27 exons and flanking regions of the CF transmembrane conductance regulator gene. We identified 22 mutations, four of which are novel, viz. 711+5GA, R709X, 3132delTG and 2790-2AnG, and we characterised 90.2% (203/225) of the CF chromosomes. Taking advantage of the homogeneity of the sample, an evaluation of the most important clinical parameters, assessed at the age of 12 years, is presented. We confirm some previously reported genotype-phenotype correlations and we report a new nonsense mutation (R709X) associated with a pancreatic sufficient phenotype.     

Tyrosinemia type 1 — complex splicing defects and a missense mutation in the fumarylacetoacetase gene

Two mutations are reported in six tyrosinemia type 1 patients from northern Europe. In four patients, a G to A transition at nucleotide position 1009 (G¹⁰⁰⁹A) of the fumarylacetoacetase (FAH) coding sequence caused aberrant splicing by introducing an acceptor splice site within exon 12, thereby deleting the first 50 nucleotides of this exon. The following exon-intron boundary was frequently missed, and a cryptic donor splice site within intron 12 caused a partial intron 12 retention of 105 bp. This point mutation alternatively gave a glycine 337 to serine substitution in instances of correct splicing. The mutation is rapidly detected by PvuII digestion of polymerase chain reaction (PCR)-amplified genomic DNA. Another mutation, g⁺⁵a in the intron 12 donor splice site consensus sequence (IVS12 g⁺⁵a), was found in five of the patients. This caused alternative splicing with retention of the first 105 nucleotides of intron 12, exon 12 skipping, and a combined deletion of exons 12 and 13. Rapid detection of this mutation is achieved by restriction digestion of PCR-amplified genomic DNA; a mismatch primer combined with the point mutation creates a Tru9I restriction site. One patient who was homozygous for the G¹⁰⁰⁹A mutation had a chronic form of tyrosinemia. Three patients were combined heterozygotes for G¹⁰⁰⁹A and TVS12 g⁺⁵a. Their clinical phenotypes varied from acute to chronic, indicating the impact of background genes and/or external factors on the presentation of typrosinemia type 1.     

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.     

LDL受体基因内含子15结构分析及其在家族性高胆固醇血症基因诊断中的应用

为了解人类ＬＤＬ受体基因内含子１５的遗传背景,利用长链ＰＣＲ和锚定ＰＣＲ分离了ＬＤＬ受体基因外显子１５－内含子１５－外显子１６和内含子１５的３‘末端片段。利用Ｄｙｎａｌｂｅａｄｓ固相单链分离ＰＣＲ产物直接测序法测定了内含子１５ ３’末端１２２２个碱基序列。序列显示：３‘末端含有由１６个碱基组成的典型３’末端剪接位点;３‘端上游第３１个碱基处含有经典分支位点,除了经典分支位点外,在３’末端上游第２０     

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.     

Human familial and sporadic breast cancer: analysis of the coding regions of the 17β-hydroxysteroid dehydrogenase 2 gene (EDH17B2) using a single-strand conformation polymorphism assay

17-Hydroxysteroid dehydrogenase (17HSD) is one of the key enzymes in estrogen metabolism, catalyzing the reversible reaction between estradiol and the less active estrogen, estrone. The gene encoding this enzyme, EDH17B2, has been mapped to chromosome 17, region q12–q21, in the vicinity of BRCA1, an as yet unidentified gene that appears to be involved in familial breast cancer and in familial ovarian cancer. The possibility that EDH17B2 gene is the same as BRCA1 was tested by screening for mutations in the coding regions of EDH17B2, using a polymerase chain reaction/single-strand conformation polymorphism method. An AG transition creating a new BstUI site at exon 6 was the only frequent sequence alteration found in the coding region of the gene. This mutation also led to an amino acid substitution of serine to glycine at position 312 (312^S312^G) in the 17HSD protein. Since the nucleotide change was detected both in specimens from patients with familial or sporadic cancer and in control samples, and at similar rates, this mutation appears to be of a polymorphic nature. In addition, a rare polymorphism located at intron 5 was detected. This CT substitution creates a BbvI site and is not thought to have any effect on 17HSD activity. The results indicate that there are no major alterations in the coding areas of EDH17B2 and thus studies testing the hypothesis that EDH17B2 may be the same as BRCA1 should be extended to the promoter and regulatory elements of EDH17B2.     

Genetic Analysis of Hispanic Individuals with Cystic Fibrosis

We have performed molecular genetic analyses of Hispanic individuals with cystic fibrosis (CF) in the southwestern United States. Of 129 CF chromosomes analyzed, only 46% (59/129) carry ΔF508. The G542X mutation was found on 5% (7/129) of CF chromosomes. The 3849+10kbC→T mutation, detected primarily in Ashkenazi Jews, was present on 2% (3/129). R1162X and R334W, mutations identified in Spain and Italy, each occurred on 1.6% (2/129) of CF chromosomes. W1282X and R553X were each detected once. G551D and N1303K were not found. Overall, screening for 22 or more mutations resulted in detection of only 58% of CF transmembrane conductance regulator gene mutations among Hispanic individuals. Analysis of KM19/XV2c haplotypes revealed an unusual distribution. Although the majority of ΔF508 mutations are on chromosomes of B haplotypes, the other CF mutations are on A and C haplotypes at higher-than-expected frequencies. These genetic analyses demonstrate significant differences between Hispanic individuals with CF and those of the general North American population. Assessment of carrier/affected risk in Hispanic CF individuals cannot, therefore, be based on the mutation frequencies found through studies of the general population but must be adjusted to better reflect the genetic makeup of this ethnic group. Further studies are necessary to identify the causative mutation(s) in this population and to better delineate genotype/phenotype correlations. These will enable counselors to provide more accurate genetic counseling.     

Frequencies of cystic fibrosis mutations in the Maine population: high proportion of unknown alleles in individuals of French-Canadian ancestry

Cystic fibrosis (CF) is one of the most common severe autosomal recessive disorders in Caucasian populations. A mutation in the cystic fibrosis transmembrane conductance regulator (CFTR) gene causes this disorder. Reported here is the first analysis of CF mutations in the Maine population. We have screened 263 CF chromosomes for 16 previously reported mutations. Analysis of DNA from 124 apparently unrelated CF patients and 15 obligate carrier parents (whose partner and affected child were unavailable for study) resulted in the identification of 91% of the CF alleles and complete genotyping of 85% of the patients. The frequencies (%) of these mutations in the Maine population are ΔF508 (75% of the chromosomes), G85E (0.76), R117H (0.76), I148T (1.1), 621+1G→T (1.1), 711+1G→T (3.0), A455E (1.1), 1717-1G→A (1.1), G542X (1.9), G551D (1.9), R560T (0.76), Y1092X (0.38), W1282X (0.38), and N1303K (1.5). The exon 10 mutation, ΔI507, and the exon 11 mutation, R553X, were not observed. Surprisingly, whereas only 5% of the alleles remain unidentified in the non-French population, the unidentified proportion in the French population is 19%. CF testing for the Maine population will be further improved as the as yet unidentified CF mutations in this population are characterized. Received: 17 January 1996 / Revised: 28 February 1996