The incidence of cystic fibrosis in Scotland calculated from heterozygote frequencies

The incidence of cystic fibrosis (CF) has previously been calculated from epidemiological surveys and from neonatal screening. With the cloning of the CF gene it has become possible to derive incidence figures from heterozygote frequencies, provided that the distribution of mutant alleles among healthy carriers is the same as among affected people. We have estimated the allele frequencies for four CF mutations, ΔF508, G551D, G542X and R117H, in 14 360 unselected women undergoing antenatal heterozygote screening. The proportion of R117H, an allele of known mild effect, was much greater for heterozygotes than for homozygotes. The incidence of CF was therefore calculated from the heterozygote frequencies of ΔF508, G551D and G542X in a larger cohort of 27 161 successively screened women. The point estimate for the incidence of CF in the Scottish population was 1 in 1984, with 95% confidence intervals of 1 in 1692 to 1 in 2336.     

Mutation analysis and haplotype correlation for 139 cystic fibrosis patients from the Nebraska Regional Cystic Fibrosis Center

Cystic fibrosis (CF) is the most common autosomal recessive disorder in Caucasian populations with an approximate frequency of one in 2,500 live births and a carrier frequency of one in 25. We studied 400 individuals seen at The Nebraska Regional Cystic Fibrosis Center that included 139 CF patients, 206 parents, and 55 unaffected siblings to determine the frequency of the ΔF508, R117H, G542X, S549R/N, G551D, R553X, R560T, and W1282X mutations. In addition, we determined haplotypes on each of these individual's chromosomes using four markers that included XV-2c, KM-19, pMP6d.9, and G2. Results from this study showed that the ΔF508 mutation was present in 70% of CF chromosomes. Of the 139 CF patients 74 (53%) were homozygous for the ΔF508 deletion, 47 (34%) were heterozygous for the ΔF508 deletion and an unknown mutation, and 18 (13%) carried two unknown mutations. Four additional-mutations were also found in our population and included G542X (6%), G551D (5%), R553X (4%), and R560T (1%). One patient was documented to be a compound heterozygote for G542X/G551D. A polymorphism, F508C, that has previously been reported in several families was also present in our study. The most common haplotype associated with the ΔF508 deletion in our CF patients was the E haplotype (CF Consortium B) while other mutations were associated with a variety of haplotypes. © 1993 Wiley-Liss, Inc.     

Severity of chest disease in cystic fibrosis patients in relation to their genotypes.

A detailed comparison of the severity of chest disease with mutational status was carried out by cross sectional study of 127 cystic fibrosis patients, aged 1 to 31 years, living in Wales. Lung disease was classified according to severity, depending on pulmonary function tests (carried out on 76 patients) and chest radiograph status; information was obtained also on age at diagnosis in relation to severity of chest disease and colonisation with Pseudomonas species. Genotypes were determined by analysis for the mutations delta F508, delta I507, G551D, R553X, G542X, R117H, R560T, 1717--IG > A, and 621 + 1G > T. CF patients homozygous positive and heterozygous for the delta F508 deletion showed a significant decline of lung function with age. Unlike other studies, we did not find patients homozygous positive for the delta F508 deletion to have poorer lung function compared with heterozygous patients. Patients with the genotype 621 + IG > T/delta F508 tended to have more severe chest disease than the delta F508 homozygous patients in the same age group. There was some evidence that four patients heterozygous for R117H have mild chest disease.     

Prevalence of cystic fibrosis mutations in the East German population.

A representative multicenter cystic fibrosis (CF) mutation analysis on about half of all known cystic fibrosis patients of the 5 East German L?nder is reported. Analyses for 17 mutations, among them Delta F508, R553X, G542X, S549R,N,I, G551D, S1255X, R347P,H, and Y122X, were performed. As expected, the delta F508 mutation in exon 10 of the CFTR gene is the major gene alteration causing CF in our patients. However, in comparison to studies from Western Germany, a significantly lower percentage of just over 60% is found in our patients, resembling data obtained from slavonic populations. The severe phenotype of cystic fibrosis is most frequently associated with homozygosity for the delta F508 mutation. No particular allele association could be found with the intermediate and mild phenotypes of this disease. The next most frequent of the investigated mutations is R553X (13.3% of non-delta F chromosomes) followed by R347P (9.2%) and G542X (4.4%).     

Predicting the risk of cystic fibrosis with abnormal ultrasound signs of fetal bowel: results of a French molecular collaborative study based on 641 prospective cases

Hyperechogenic fetal bowel is prenatally detected by ultrasound during the second trimester of pregnancy in 0.1-1.8% of fetuses. It has been described as a normal variant but has often been associated with severe diseases, notably cystic fibrosis (CF). The aim of our study was to determine the risk of CF in a prospective study of 641 fetuses with ultrasonographically abnormal fetal bowel and the residual risk when only one mutation is detected in the fetus. Fetal cells and/or parental blood cells were screened for CFTR mutations. Two screening steps were used, the first covering the mutations most frequently observed in French CF patients (mutation detection rate of 70-90%) and, when a CF mutation was detected, a DGGE-sequencing strategy. We observed a 3.1% risk of CF when a digestive tract anomaly was prenatally observed at routine ultrasound examination. The risk was higher when hyperechogenicity was associated with bowel dilatation (5/29; 17%) or with the absence of gall bladder (2/8; 25%). The residual risk of CF was 11% when only one CF mutation was detected by the first screening step, thereby justifying in-depth screening. Mutations associated with severe CF (DeltaF508 mutation) were more frequently observed in these ultrasonographically and prenatally detected CF cases. However, the frequency of heterozygous cases was that observed in the normal population, which demonstrates that heterozygous carriers of CF mutations are not at increased risk for hyperechogenic bowel. In conclusion, fetal bowel anomalies indicate a risk of severe cystic fibrosis and justify careful CFTR molecular analysis.     

Calculating posterior cystic fibrosis risk with echogenic bowel and one characterized cystic fibrosis mutation: avoiding pitfalls in the risk calculations

We describe a general approach to derive fetal risk following two separate test results that each raise the likelihood of the same fetal abnormality without clearly determining whether the abnormality exists. Echogenic bowel observed on fetal ultrasonography may have multiple causes, including an a priori risk of approximately 1% of cystic fibrosis (CF). On numerous occasions our laboratory tests have detected only normal cystic fibrosis transmembrane regulator (CFTR) alleles in fetuses with echogenic bowel. This result indicates that another cause most likely explains the abnormal ultrasound finding. One of our tested fetuses was heterozygous for the deltaF508 CFTR mutation and had a normal karyotype. Over 770 CFTR mutations have been described, and a significant proportion of parental mutant alleles could not be detected by our 25-mutation test. Further mutation analysis demonstrated that the fetus' mother carried the deltaF508 mutation but the father (of different ethnic background than the mother) did not carry a detectable mutation. Thus, this test result substantially increased the risk of the fetus having CF, while still not giving a definitive answer to whether the fetus was affected. A rigorous mathematical analysis determined that the 1% risk of CF following ultrasound study was increased to slightly under 12% following DNA analysis. The case is described, and the mathematical formulas are explained and illustrated with examples, along with a review of conditional probability (Appendix 2).     

Molecular analysis of northwestern Mexican patients with cystic fibrosis: screening of 10 known mutations. Mutations in brief no. 185. Online

We have analyzed 45 unrelated Northwestern Mexican patients with Cystic Fibrosis for 10 known CF mutations (DF508, G542X, G551D. R553X, W1282X, NI303K, R334W, R347H, S549R, and R1162X). Screening was performed on exons 7, 10, 11, 19, 20 and 21 using standard methods such as polymerase chain reactions, reverse dot blot hybridization (non-radioactive), and restriction enzyme digestion. The analysis for these ten mutations permitted the identification of only two mutations in 37.7% of CF chromosomes in this sample. The major mutation, delta F508, accounts for 34.4% of CF chromosomes. Of the 45 CF patients 9 (20.0%) were homozygous delta F508 deletion, 11 (24.4%) were heterozygous for the delta F508 mutation and an unknown mutation. One additional mutation G542X was also found in 3 chromosomes in our population (3.3%). Two patients were documented to be a compound heterozygote for DF508/G542X, and other one heterozygous for G542X and an unknown mutation. Therefore 62.2% of chromosomes remain uncharacterized.     

Cystic fibrosis mutations among African Americans in the southeastern United States.

Since the cloning of the cystic fibrosis (CF) gene and the identification of delta F508, the most common CF mutation, screening the general population for CF has been vigorously debated. Adding to the controversy is the question of whether screening should be offered to African Americans, whose incidence of CF (1/17,000) is much lower than that of whites (1/2500). We tested for five common mutations (delta F508, G551D, G542X, R553X, and N1303K) in order to determine the frequency of common mutations in African Americans with CF from the southeastern United States. delta F508 was found on 50% of CF chromosomes; 46% of CF mutations were undetermined mutations. Our data indicate that at the current detection rate, the sensitivity of CF screening in African Americans would be appreciably lower than that of whites, and thus their inclusion in screening programs probably would not be warranted.     

CFTR gene: molecular analysis in patients from South Brazil

Cystic fibrosis (CF) is the most common genetic disease among Caucasians. The CF gene, named cystic fibrosis transmembrane conductance regulator (CFTR), codifies a protein that acts as a channel through the epithelial membrane. The present work aimed (1) to detect sequence alterations in the nucleotide binding regions and at the membrane spanning domain of the CFTR gene and (2) to detect the following frequent mutations R347P, R347H, R334W, and Q359K (located in exon 7), DeltaF508 (located in exon 10), G542X, G551D, R553X, and S549N (located in exon 11), W1282X (located in exon 20), and N1303K (located in exon 21). Seventy-seven unrelated CF patients were analyzed, who were previously diagnosed and currently under treatment at the Pneumology Service of our hospital. Regions of interest were amplified by PCR using specific primers. Each sample was analyzed by a non-radioactive single-stranded conformational polymorphism (SSCP) analysis technique and restriction enzyme digestion. The DeltaF508 mutation was found in 48.7% of the alleles. Frequencies of G542X, R334W, R553X, and W1282X mutations in our population were 3.25, 1.3, 0.65, and 0.65%, respectively. No alleles were found to carry mutations G551D, R334W, R347P, R347H, Q359K, S549N, and N1303K, which were included in the screening protocol. This study allowed the characterization of 84 out of 154 CF mutant alleles (54.5%). The incidence of main CF mutations analyzed was similar to that of the south European population. Mutation data presented here will be useful for designing new DNA testing strategies for CF in South Brazil.     

Genetic testing for cystic fibrosis: evaluation of the Elucigene CF20 kit in blood and buccal cells

Routine determination of mutations in cystic fibrosis requires accurate, rapid, reliable and low-cost methods, permitting the simultaneous detection of multiple mutations. The Elucigene CF20 kit developped by Cellmark Diagnostics, uses multiplex ARMS, which allows the screening for 20 CFTR gene mutations (deltaF508, G542X, N1303K, 1717-1G>A, G551D, W1282X, R553X, deltaI507, 1078delT, 2183AA>G, 3849+10kbC>T, R1162X, 621+1G>T, R334W, R347P, 3659delC, R117H, S1251N, E60X, A455E ) in a work day without specific instrumentation. The kit distinguishes between homozygotes and heterozygotes for deltaF508, but not for rare mutations. The kit detects from 68 to 92% of defective alleles in Caucasians. We evaluate the kit in a blind study in two independent laboratories. Thirty blood samples and thirty mouthwash samples from CF patients, carriers and unaffected individuals were analysed by the Elucigene CF20 kit. All the samples were previously analysed by denaturing gradient gel electrophoresis and sequencing. The Elucigene CF20 kit consists of three multiplexes. Each mutiplex contains ARMS specific primers for six to eight mutations and two control reactions. The absence of the upper control fragment indicates that a repeat test is required. We demonstrated a first time amplification rate of 98.3%: of the 60 samples tested, one required a reamplification. Results compared with the reference method demonstrated that in all cases where one or more of the 20 mutations detected by the kit were present in the test set, the kit accurately identified them. Reproducibility was assessed by repeating the analysis of a blood and mouthwash sample five times. Cross reactivity between R117C and R117H, R117P and R117H, R347P and R347H, deltaI507 and deltaF508, G551D and R553X were evaluated. Only a cross reactivity between R347P and R347H was observed. The kit is specially useful for first line study of patients and carrier identification.     

Andrology: Results of retroactive testing of human semen donors for cystic fibrosis and human immunodeficiency virus by polymerase chain reaction

Retroactive testing for cystic fibrosis carrier status was performedon 149 semen donors and 100 donor applicants; 162 human immunodeficiencyvirus (HIV-1) sero-negative non-active semen donors and 45 HIV-1sero-negative actively donating semen donors were also retroactivelytested for HIV-1 by polymerase chain reaction (PCR). The 249individuals tested for cystic fibrosis were examined for sevenmutations including F508, G542X, S5491, S549N, G551D, R553X,and W1282X. Of 149 retroactively tested donors, five (3.4%)were determined to be heterozygous carriers of the F508 mutationfor cystic fibrosis. One of the 100 donor applicants was alsoheterozygous for F508. The 207 HIV-1 sero-negative donors hadan average of 15.4 (range 2–45) HIV antibody tests duringan average of 15.6 (range 1–68) months of donations. Nodonors had positive seroconversion. These donors also testednegative for HIV by PCR. Cystic fibrosis testing of donor applicantsprevents known carriers from being used for artificial inseminationby donor therapy and reduces substantially the risk of an offspringbeing born with the disease. With stringent donor selectionand exclusion of high-HIV-risk applicants, the occurrence ofHIV infection and subsequent seroconversion in donor populationsshould be very infrequent.     

The incidence of different cystic fibrosis mutations in the Scottish population: effects on prenatal diagnosis and genetic counselling.

We present an analysis of the frequency of 16 different cystic fibrosis (CF) mutant alleles in the Scottish population. Each allele was detected in DNA amplified by the polymerase chain reaction (PCR) either directly on polyacrylamide gels, on agarose gels after restriction enzyme digestion, or by using allele specific oligonucleotides. Among 506 CF chromosomes, of predominantly Scottish origin, the frequencies of the different mutations were delta F508 0.71, G551D 0.05, G542X 0.04, R117H 0.01, 1717-1G----A 0.01, A455E + delta I507 + R553X + R560T + W1282X + 621 + 1G----T combined 0.03, unpublished 0.01, and unknown 0.13. No examples of D110H, R347P, S549N, S549I, or 2566ins AT mutations were found. The relevance of this type of analysis for both prenatal diagnosis and heterozygote screening is discussed.     

Partial CFTR genotyping and characterisation of cystic fibrosis patients with myocardial fibrosis and necrosis

Myocardial necrosis and fibrosis is a rare complication of cystic fibrosis (CF) causing sudden and unexpected death in infancy due to cardiac arrest. Characteristic morphological lesions are recognisable postmortem. The 18 CF patients with this complication had varied clinical features including mild pulmonary involvement, early onset severe pancreatic insufficiency, and profound electrocardiogram (ECG) changes. In this group of patients, 5 were deltaF508 homozygotes, 1 was deltaF508/ N1303K and 1 was a deltaF508/M compound heterozygote. A pair of affected siblings (deltaF508 homozygotes) were fully concordant for myocardial involvement and for the general course of the disease. The co-existence of a genetic predisposition to myocardial lesions resulting most probably from severe cystic fibrosis transmembrane (CFTR) genotypes (such as deltaF508/deltaF508, deltaF508/N1303K) and deficiency of certain trophic factors necessary for metabolism of the myocardium, are postulated to cause myocardial complications in CF leading to circulatory failure and early death.     

A Single-tube multiplex system for the simultaneous detection of 10 common cystic fibrosis mutations

We describe a nonisotopic single-tube polymerase chain reaction (PCR) multiplex system that detects 10 of the more common cystic fibrosis (CF) mutations (ΔF508, ΔI507, V520F, G551D, G542X, R553X, R117H, 621 + lG→T, N1303K, A455E). The use of this method detects approximately 90% of the CF alleles in the British population. Five exons of the CF gene are amplified simultaneously by PCR, followed by an overnight triple enzyme restriction digest, and then resolved by high-resolution gel acrylamide electrophoresis. © 1995 Wiley-Liss, Inc.     

Cystic fibrosis in Greece: molecular diagnosis,haplotypes, prenatal diagnosis and carrier identification amongst high-risk individuals

Cystic fibrosis (CF) mutation analysis on 437 CF patients, characterized 80 different mutations (20 so far specific to our population) accounting for 91% of CF genes and generating 103 different genotypes. Eight mutations were common [F508del (53.4%), 621+1G>T (5.7%), G542X (3.9%), N1303K (2.6%), 2789+5G>A (1.7%), 2183AA>G (1.4%), E822X (1.4%), R1158X (1%)], 12 showed frequencies between 0.5% and 1%, while the remaining (60) were very rare (1 to 3 alleles). Denaturing gradient gel electrophoresis (DGGE) screening of 12 exons (3, 4, 7, 10, 11, 13, 14b, 16, 17b 20 and 21) detected 85.5% of CF alleles. Haplotypes for eight diallelic and three microsatellite markers have been characterized for the common, a few rare and novel Greek mutations. Results of 165 prenatal diagnoses (including 49 due to bowel hyperechogenicity), testing a total of 41 different parental genotypes, are reported. One hundred and sixteen prenatal tests resulted in 22 affected, 59 heterozygous, 34 normal fetuses and one incomplete diagnosis. Of the 49 echogenic bowel fetuses, 3 were heterozygotes. Carrier screening was initiated, with emphasis on individuals and couples in high-risk groups - with a family history of CF, one partner with CF, and couples with male infertility seeking in vitro fertilization (IVF). Mutation analysis on 672 individuals (120 couples, 91 unaffected CF siblings, 283 CF family relatives and 58 general population subjects), identified a total of 176 heterozygotes and 7 couples where both partners were CF heterozygotes. Prenatal diagnosis was performed in 4 cases and 3 were counseled on the availability of a prenatal test.     

Sweat electrolyte and cystic fibrosis mutation analysis allows early diagnosis in Brazilian children with clinical signs compatible with cystic fibrosis

A total of 540 individuals with clinical signs suggestive of cystic fibrosis (CF) was studied. The sweat chloride was measured and the DF508, G542X, R553X, and W1282X mutations of the CF gene were screened by polymerase chain reaction (PCR). With this approach the diagnosis of CF was confirmed in 12 children, while 7 additional cases, who are heterozygous for the DF508 mutation, have had minor clinical signs. The frequency of the DF508 allele among the 540 individuals was approximately 3%. The mean age of children diagnosed with CF was 1.81 years, which is significantly earlier than in other studies of the Brazilian population. We also demonstrated that this approach has important clinical implications for earlier and adequate treatment, which was shown to be fundamental for increasing significantly the quality of life and life expectancy. This is particularly true in countries such as Brazil where most CF cases remain undiagnosed, mainly in families of low socio-economical status. Am. J. Med. Genet. 76:288–290. © 1998 Wiley-Liss, Inc.     

Mutation analysis of 184 cystic fibrosis families in Wales.

We describe a molecular analysis of 184 cystic fibrosis (CF) families in Wales. To determine accurate frequency data for the CF mutations in the Welsh population, families with at least three Welsh grandparents were strictly regarded as Welsh. Of these 74 families, we have identified approximately 90% of mutations causing CF, with delta F508 accounting for 71.8% and 621 + 1G greater than T 6.7%. We observed a significant difference between the Welsh and Scottish frequencies of 621 + 1G greater than T. To allow the rapid and efficient screening for the more common mutations we modified a multiplex used by Watson et al enabling the detection of delta F508, G551D, and R553X simultaneously with 621 + 1G greater than T. In parallel to this system we ran the Cellmark Diagnostics ARMS multiplex kit, which detects delta F508, 621 + 1G greater than T, G551D, and G542X. RFLP analysis of the 184 families shows that the delta F508 chromosomes are almost exclusively found on the B haplotype (XV2c 1, KM19 2); the other CF mutations have more heterogeneous backgrounds. Strong haplotype correlations exist between the markers XV2c, KM19, D9, and G2 and the other CF mutations. Haplotype data suggest that there are at least seven mutations that remain to be identified in these families.     

Genotype-phenotype relationship in 12 patients carrying cystic fibrosis mutation R334W.

We present a phenotype-genotype correlation analysis in 12 patients with cystic fibrosis (CF) carrying the mutation R334W in the CFTR gene. The clinical data obtained for this group were compared with the clinical data of deltaF508/deltaF508 patients. Current age and age at diagnosis were significantly higher in the R334W mutation group (p=0.028 and p=0.0001). We found a lower rate of Pseudomonas aeruginosa colonisation in patients carrying the R334W mutation, although the difference was not found to be statistically significant. However, we found a statistically significant higher age of onset of Pseudomonas aeruginosa colonisation (p=0.0036) in the group of patients with the R334W mutation. Thirty three percent of R334W patients were pancreatic insufficient, significantly lower than the deltaF508/deltaF508 patients (p=0.004). We also found that the weight expressed as a percentage of ideal weight for height was significantly higher in patients with the R334W mutation (p=0.0028).     

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.