Gradient of distribution in Europe of the major CF mutation and of its associated haplotype. European Working Group on CF Genetics (EWGCFG)

Targeted locus amplification reveals heterogeneity between and within CFTR genotypes and association with CFTR function in patient-derived intestinal organoids

BACKGROUND

Cystic fibrosis (CF) disease severity can be highly variable, even between people with CF (pwCF) with similar genotypes. Here we use patient-derived intestinal organoids to study the influence of genetic variation within the cystic fibrosis transmembrane conductance regulator (CFTR) gene on CFTR function.

METHODS

Organoids of F508del/class I, F508del/S1251N and pwCF with only one detected CF-causing mutation were cultured. Allele-specific CFTR variation was investigated using targeted locus amplification (TLA), CFTR function was measured using the forskolin-induced swelling assay and mRNA levels were quantified using RT-qPCR.

RESULTS

We were able to distinguish CFTR genotypes based on TLA data. Additionally, we observed heterogeneity within genotypes, which we were able to link to CFTR function for S1251N alleles.

CONCLUSIONS

Our results indicate that the paired analysis of CFTR intragenic variation and CFTR function can gain insights in the underlying CFTR defect for individuals where the disease phenotype does not match the CFTR mutations detected during diagnosis.

Genetics of cystic fibrosis: Basics

Cystic fibrosis (CF) is an autosomal recessive genetic disorder whose responsible gene - the CFTR gene - was discovered 30 years ago by a positional cloning strategy. This gene, which encodes a chloride channel, contains more than 2,000 mutations including a major one (p.Phe508del). This discovery has led to considerable progress in the understanding of the pathophysiology of CF as well as in the management of patients and their families. It has also paved the way for the development of specific therapies for the disease. From an epidemiological point of view, the incidence of CF, which shows loco-regional variations, is now estimated at 1/4,700 live births in France. The face of CF has dramatically changed over the past decades: CF has gradually become a disease of the adult with, today, more than 50% of the patients being 18 years old or more and a median predicted survival age that exceeds 45 years. © 2020 French Society of Pediatrics. Published by Elsevier Masson SAS. All rights reserved.

Prevalence of cholesteryl ester storage disease among hypercholesterolemic subjects and functional characterization of mutations in the lysosomal acid lipase gene

Lysosomal acid lipase hydrolyzes cholesteryl esters and triglycerides contained in low density lipoprotein. Patients who are homozygous or compound heterozygous for mutations in the lysosomal acid lipase gene (LIPA), and have some residual enzymatic activity, have cholesteryl ester storage disease. One of the clinical features of this disease is hypercholesterolemia. Thus, patients with hypercholesterolemia who do not carry a mutation as a cause of autosomal dominant hypercholesterolemia, may actually have cholesteryl ester storage disease. In this study we have performed DNA sequencing of LIPA in 3027 hypercholesterolemic patients who did not carry a mutation as a cause of autosomal dominant hypercholesterolemia. Functional analyses of possibly pathogenic mutations and of all mutations in LIPA listed in The Human Genome Mutation Database were performed to determine the pathogenicity of these mutations. For these studies, HeLa T-REx cells were transiently transfected with mutant LIPA plasmids and Western blot analysis of cell lysates was performed to determine if the mutants were synthesized in a normal fashion. The enzymatic activity of the mutants was determined in lysates of the transfected cells using 4-methylumbelliferone-palmitate as the substrate. A total of 41 mutations in LIPA were studied, of which 32 mutations were considered pathogenic by having an enzymatic activity <10% of normal. However, none of the 3027 hypercholesterolemic patients were homozygous or compound heterozygous for a pathogenic mutation. Thus, cholesteryl ester storage disease must be a very rare cause of hypercholesterolemia in Norway.

Mitochondrial DNA genetic diversity and LCT-13910 and deltaF508 CFTR alleles typing in the medieval sample from Poland

We attempted to confirm the resemblance of a local medieval population and to reconstruct their contribution to the formation of the modern Polish population at the DNA level. The HVR I mtDNA sequence and two nuclear alleles, LCT-13910C/T SNP and deltaF508 CFTR, were chosen as markers since the distribution of selected nuclear alleles varies among ethnic groups. A total of 47 specimens were selected from a medieval cemetery in Cedynia (located in the western Polish lowland). Regarding the HVR I profile, the analyzed population differed from the present-day population (P = 0.045, F(st) = 0.0103), in contrast to lactase persistence (LP) based on the LCT-13910T allele, thus indicating the lack of notable frequency changes of this allele during the last millennium (P = 0.141). The sequence of the HVR I mtDNA fragment allowed to identify six major haplogroups including H, U5, T, K, and HV0 within the medieval population of Cedynia which are common in today's central Europe. An analysis of haplogroup frequency and its comparison with modern European populations shows that the studied medieval population is more closely related to Finno-Ugric populations than to the present Polish population. Identification of less common haplogroups, i.e., Z and U2, both atypical of the modern Polish population and of Asian origin, provides evidence for some kind of connections between the studied and foreign populations. Furthermore, a comparison of the available aDNA sequences from medieval Europe suggests that populations differed from one another and a number of data from other locations are required to find out more about the features of the medieval gene pool profile.

Assessing the Disease-Liability of Mutations in CFTR

Over 1900 mutations have been reported in the cystic fibrosis transmembrane conductance regulator (CFTR), the gene defective in patients with cystic fibrosis. These mutations have been discovered primarily in individuals who have features consistent with the diagnosis of CF. In some cases, it has been recognized that the mutations are not causative of cystic fibrosis but are responsible for disorders with features similar to CF, and these conditions have been termed CFTR-related disorders or CFTR-RD. There are also mutations in CFTR that do not contribute to any known disease state. Distinguishing CFTR mutations according to their penetrance for an abnormal phenotype is important for clinical management, structure/function analysis of CFTR, and understanding the molecular and cellular mechanisms underlying CF.

An evolutionary approach to the high frequency of the Delta F508 CFTR mutation in European populations

The diffusion of the cattle pastoralism across Europe during the Neolithic period was probably accompanied by the emergence and spread of diverse contagious diseases that were unknown in the Paleolithic and that would have affected the frequency of genes directly or indirectly associated with differential susceptibility and/or resistance to infectious pathogens. We therefore propose that the high frequency of the CFTR gene, and in particular, the common Delta F508 allele mutation in current European and European-derived populations might be a consequence of the impact of selective pressures generated by the transmission of pathogenic agents from domesticated animals, mainly bovine cattle, to the man. Intestinal infectious diseases were probably a major health problem for Neolithic peoples. In such a context, a gene mutation that conferred an increased resistance to the diseases caused by pathogens transmitted by dairy cattle would have constituted a definite selective advantage, particularly in those human groups where cow's milk became an essential component of the diet. This selective advantage would be determined by an increased resistance to Cl(-)-secreting diarrheas of those individuals carrying a single copy of the Delta F508 CFTR mutation (heterozygote resistance). This hypothesis is supported by the strong association between the geography of the diffusion of cattle pastoralism (assessed indirectly by the lactase persistence distribution), the geographic distribution of a sizeable number of HLA alleles (as indicative of potential selective pressures generated by epidemic mortality) and the geographic distribution of the most common mutation causing cystic fibrosis (Delta F508). The systematic interaction of humans with infectious pathogens would have begun in northern Europe, among the carriers of the Funnel Beaker Culture, the first farmers of the North European plain, moving progressively to the south with the dissemination of the cattle pastoralism. This gradual exposure to epidemic mortality among populations located further and further south in Europe as cattle pastoralism expanded could have generated differences in CFTR gene frequencies, thereby shaping the latitudinal frequency gradients observed in present-day European populations.

Hierarchical fine mapping of the cystic fibrosis modifier locus on 19q13 identifies an association with two elements near the genes CEACAM3 and CEACAM6

On 19q13, TGFB1 and the cystic fibrosis modifier 1 locus (CFM1) have been identified as modifiers of the course of the monogenic disease cystic fibrosis (CF). Recently, we have described a transmission disequilibrium at the microsatellite D19S197, localized between TGFB1 and CFM1. To map the corresponding molecular variants, we have selected informative SNP markers within a 600-kb area and compared two-marker-haplotype-distributions between phenotypically contrasting sib pair groups, intending to type only phylogenetically old markers by aiming for close-to-maximal polymorphism information content of the SNPs. Starting with a seed set of five SNPs that cover intermarker distances of up to 50 kb, we have iteratively added more SNPs to the map, until we could identify two genomic fragments of 3,289 and 2,052 bp for which pairs with contrasting phenotypes showed different haplotype distributions on the final 17-SNP-map (P(raw) = 0.0002, P(corr17SNPs) = 0.0106 and P(raw) = 0.0008, P(corr17SNPs) = 0.0469, respectively). Resequencing of these fragments of four unrelated individuals for each element showed that the mildly and severely affected pairs differ in seven SNPs and concordant pairs differ from discordant pairs in five SNPs. Annotation of these variants indicate that CEACAM6 and a regulatory element near the 3' end of CEACAM3 are associated with CF disease severity and intrapair discordance, respectively. While our approach was only guided by the markers' position, the involvement of genes from the CEACAM family in host defense and innate immunity designates these proteins as likely modifiers of the multi-organ disease cystic fibrosis which is known for its cytokine imbalance and pro-inflammatory phenotype.

Biological V. Social Definitions of Race: Implications for Modern Biomedical Research

Misconceptions concerning the concordance of biological and social definitions of race are ongoing in American society. This problem extends beyond that of the lay public into the professional arena, especially that of biomedical research. This continues, in part, because of the lack of training of many biomedical practitioners in evolutionary thinking. This essay reviews the biological and social definitions of race, examining how understanding the evolutionary mechanisms of disease is crucial to addressing ongoing health disparities. Finally it concludes by laying bear the fallacies of “race-specific” medicine.

CFTR allelic heterogeneity in Brazil: historical and geographical perspectives and implications for screening and counseling for cystic fibrosis in this country

The goal of the present study was to provide a complete and updated spectrum of cystic fibrosis (CF) transmembrane conductance regulator (CFTR) gene mutations in the Brazilian population combining all available in silico data for patients with CF in Brazil, including founder background and migration flow that consisted of the actual genetic pool of the Brazilian population. Information sources in international databases (PUBMED and SCIELO) were searched. The Brazilian population shows a wide variation in the frequency of CFTR mutations in states Rio Grande do Sul (RS), Santa Catarina (SC), Paraná (PR), São Paulo (SP), Rio de Janeiro (RJ), Minas Gerais (MG), Pará (PA) and Bahia (BA); this variation includes the most common mutation p.F508del. Apparently, this frequency variation is because of the different ethnic compositions. States such as SC and PR have a greater European admixture with almost 90% of CF alleles identified. In other states, such as BA, higher frequency of alleles that are common among African populations is seen. Overall, the CFTR mutational spectrum indicates the presence of European, African and Amerindian ethnic groups in the contemporary Brazilian CF patients. Here, we present an analysis of the CFTR allelic heterogeneity and discuss the origin of its genetic composition, in an attempt to provide improved perspective for the CF population screening in Brazil and genetic counseling.

XV-2c/KM19 haplotypes analysis of cystic fibrosis patients from western Mexico

The analysis of polymorphic markers within or closely linked to the cystic fibrosis transmembrane regulator (CFTR) gene is useful as a molecular tool for carrier detection of known and unknown mutations. To establish the association between mutations in the CFTR gene in western Mexican cystic fibrosis (CF) patients, the distribution of XV2c/KM19 haplotypes was analyzed by PCR and restriction enzyme digestion in 384 chromosomes from 74 CF patients, their unaffected parents, and normal subjects. The haplotype analysis revealed that haplotype B was present in 71.9% of CF chromosomes compared to 0% of non-CF chromosomes. The F508del and G542X mutations were strongly associated with haplotype B (96.7% and 100% of chromosomes, respectively). The haplotype distribution of the CF chromosomes carrying other CFTR mutations had a more heterogeneous background. Our results show that haplotype B is associated with CFTR mutations. Therefore, haplotype analysis is a suitable alternate strategy for screening CF patients with a heterogeneous clinical picture from populations with a high molecular heterogeneity where carrier detection programs are not available. In addition, it may be a helpful diagnostic tool for genetic counseling and carrier detection in the relatives of CF patients and in couples who are planning to have children.

Expression levels of FAS are regulated through an evolutionary conserved element in intron 2, which modulates cystic fibrosis disease severity

We have analyzed frequent naturally occurring variants in the autogene FAS in two independent cystic fibrosis (CF) patient populations. Analysis of FAS expression levels from intestinal epithelial biopsies from 16 unrelated F508del-CFTR homozygotes showed a correlation between FAS intron 2 SNP rs7901656 and signals for Affymetrix GeneChip U133 Plus 2.0 probeset 204781_s_at consistent with a dominant model (P=0.0009). Genotype and haplotype analysis at six informative SNPs spanning the FAS gene locus was carried out on 37 nuclear families representing extreme clinical phenotypes that were selected from the European CF Twin and Sibling Study population of more than 300 affected sibling pairs. Case-control comparison of the haplotype composed of rs2296603-rs7901656-rs1571019 encompassing intron 2 of FAS reached significance (P=0.0246). Comparative phylogenetic analysis and functional annotation of the FAS intron 2 sequence revealed a conserved non-coding sequence surrounding rs7901656 and predicted binding sites for four transcription factors whereby the binding site of c-Rel is altered by rs7901656. Taken together, these findings from two independent CF patient cohorts indicate that allelic variants within FAS intron 2 alter FAS gene expression and that these functional variants modulate the manifestation of CF disease.

CFTR gene analysis in Latin American CF patients: heterogeneous origin and distribution of mutations across the continent

BACKGROUND

Cystic Fibrosis (CF) is the most prevalent Mendelian disorder in European populations. Despite the fact that many Latin American countries have a predominant population of European-descent, CF has remained an unknown entity until recently. Argentina and Brazil have detected the first patients around three decades ago, but in most countries this disease has remained poorly documented. Recently, other countries started publishing their results.

METHODS

We present a compilation and statistical analysis of the data obtained in 10 countries (Argentina, Brazil, Chile, Colombia, Costa Rica, Cuba, Ecuador, Mexico, Uruguay and Venezuela), with a total of 4354 unrelated CF chromosomes studied.

RESULTS

The results show a wide distribution of 89 different mutations, with a maximum coverage of 62.8% of CF chromosomes/alleles in the patient's sample. Most of these mutations are frequent in Spain, Italy, and Portugal, consistent with the origin of the European settlers. A few African mutations are also present in those countries which were part of the slave trade. New mutations were also found, possibly originating in America.

CONCLUSION

The profile of mutations in the CFTR gene, which reflects the heterogeneity of its inhabitants, shows the complexity of the molecular diagnosis of CF mutations in most of the Latin American countries.

A haplotype framework for cystic fibrosis mutations in Iran

This is the first comprehensive profile of cystic fibrosis transmembrane conductance regulator (CFTR) mutations and their corresponding haplotypes in the Iranian population. All of the 27 CFTR exons of 60 unrelated Iranian CF patients were sequenced to identify disease-causing mutations. Eleven core haplotypes of CFTR were identified by genotyping six high-frequency simple nucleotide polymorphisms. The carrier frequency of 2.5 in 100 (1 in 40) was estimated from the frequency of heterozygous patients and suggests that contrary to popular belief, cystic fibrosis may be a common, under-diagnosed disease in Iran. A heterogeneous mutation spectrum was observed at the CFTR locus in 60 cystic fibrosis (CF) patients from Iran. Twenty putative disease-causing mutations were identified on 64 (53%) of the 120 chromosomes. The five most common Iranian mutations together represented 37% of the expected mutated alleles. The most frequent mutation, DeltaF508 (p.F508del), represented only 16% of the expected mutated alleles. The next most frequent mutations were c.1677del2 (p.515fs) at 7.5%, c.4041C>G (p.N1303K) at 5.6%, c.2183AA>G (p.684fs) at 5%, and c.3661A>T (p.K1177X) at 2.5%. Three of the five most frequent Iranian mutations are not included in a commonly used panel of CF mutations, underscoring the importance of identifying geographic-specific mutations in this population.

The TNFalpha receptor TNFRSF1A and genes encoding the amiloride-sensitive sodium channel ENaC as modulators in cystic fibrosis

The CFTR mutations in cystic fibrosis (CF) lead to ion transport anomalities which predispose to chronic infection and inflammation of CF airways as the major determinants for morbidity and mortality in CF. Discordant clinical phenotypes of siblings with identical CFTR mutations and the large variability of clinical manifestations of patients who are homozygous for the most common mutation F508del suggest that both environment and genes other than CFTR contribute substantially to CF disease. The prime candidates for genetic modifiers in CF are elements of host defence such as the TNFalpha receptor and of ion transport such as the amiloride-sensitive epithelial sodium channel ENaC, both of which are encoded side by side on 12p13 (TNFRSF1A, SCNN1A) and 16p12 (SCNN1B, SCNN1G). Thirty-seven families with F508del-CFTR homozygous siblings exhibiting extreme clinical phenotypes that had been selected from the 467 pairs of the European CF Twin and Sibling Study were genotyped at 12p13 and 16p12 markers. The ENaC was identified as a modulator of CF by transmission disequilibrium at SCNN1G and association with CF phenotype intrapair discordance at SCNN1B. Family-based and case-control analyses and sequencing of SCNN1A and TNFRSF1A uncovered an association of the TNFRSF1A intron 1 haplotype with disease severity. Carriers of risk haplotypes were underrepresented suggesting a strong impact of both loci on survival. The finding that TNFRSF1A, SCNN1B and SCNN1G are clinically relevant modulators of CF disease supports current concepts that the depletion of airway surface liquid and inadequate host inflammatory responses trigger pulmonary disease in CF.

Musculoskeletal manifestations in cystic fibrosis

Although bone and joint manifestations are common in children with cystic fibrosis (CF), they have received little attention in adults. As compared to healthy individuals, bone mineral density is low, even with calcium intakes greater than 1500 mg/d. Nevertheless, calcium and phosphate levels in blood and urine are often normal, and vitamin D levels vary. Short stature with a low body mass index and central hypogonadism are the rule in these patients. Fractures and kyphosis are often reported. CF arthropathy occurs in 2-8.5% of patients. Arthritis develops, and there may be skin eruptions. Non-steroidal antiinflammatory drug therapy is effective. Hypertrophic osteoarthropathy associated with respiratory failure is present in 2-7% of patients. Rheumatoid arthritis, spondyloarthropathies, sarcoidosis, and amyloidosis have been reported in association with CF. Knee pain due to patellofemoral syndrome, quinolone-induced arthropathy, and mechanical back pain have been described. Rheumatoid factor titers are higher than in healthy controls, particularly in patients with episodic arthritis. No data are available on antiperinuclear factor or antikeratin antibody titers. Tests for antinuclear antibody are usually negative. Circulating immune complex levels and antibodies to heat shock proteins may be elevated. Antineutrophil cytoplasmic antibody of the bactericidal/permeability-increasing protein (BPI) or azurocidin (AZ) type has been reported, often in high titers (up to 40%).

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.

Cystic fibrosis: a worldwide analysis of CFTR mutations--correlation with incidence data and application to screening

Although there have been numerous reports from around the world of mutations in the gene of chromosome 7 known as CFTR (cystic fibrosis transmembrane conductance regulator), little attention has been given to integrating these mutant alleles into a global understanding of the population molecular genetics associated with cystic fibrosis (CF). We determined the distribution of CFTR mutations in as many regions throughout the world as possible in an effort designed to: 1) increase our understanding of ancestry-genotype relationships, 2) compare mutational arrays with disease incidence, and 3) gain insight for decisions regarding screening program enhancement through CFTR multi-mutational analyses. Information on all mutations that have been published since the identification and cloning of the CFTR gene's most common allele, DeltaF508 (or F508del), was reviewed and integrated into a centralized database. The data were then sorted and regional CFTR arrays were determined using mutations that appeared in a given region with a frequency of 0.5% or greater. Final analyses were based on 72,431 CF chromosomes, using data compiled from over 100 original papers, and over 80 regions from around the world, including all nations where CF has been studied using analytical molecular genetics. Initial results confirmed wide mutational heterogeneity throughout the world; however, characterization of the most common mutations across most populations was possible. We also examined CF incidence, DeltaF508 frequency, and regional mutational heterogeneity in a subset of populations. Data for these analyses were filtered for reliability and methodological strength before being incorporated into the final analysis. Statistical assessment of these variables revealed that there is a significant positive correlation between DeltaF508 frequency and the CF incidence levels of regional populations. Regional analyses were also performed to search for trends in the distribution of CFTR mutations across migrant and related populations; this led to clarification of ancestry-genotype patterns that can be used to design CFTR multi-mutation panels for CF screening programs. From comprehensive assessment of these data, we offer recommendations that multiple CFTR alleles should eventually be included to increase the sensitivity of newborn screening programs employing two-tier testing with trypsinogen and DNA analysis.

Can a place of origin of the main cystic fibrosis mutations be identified?

The genetic background of the mutations that most often cause cystic fibrosis (CF) is different from that of non-CF chromosomes in populations of European origin. It is not known whether these haplotype backgrounds could be found at high frequencies in populations in which CF is, at present, not common; such populations would be candidates for the place of origin of CF mutations. An analysis of haplotypes of CF transmembrane conductance regulator, together with their variation in specific CF chromosomes, in a worldwide survey of normal chromosomes shows (1) a very low frequency or absence of the most common CF haplotypes in all populations analyzed and (2) a strong genetic variability and divergence, among various populations, of the chromosomes that carry disease-causing mutations. The depth of the gene genealogy associated with disease-causing mutations may be greater than that of the evolutionary process that gave rise to present-day human populations. The concept of "population of origin" lacks either spatial or temporal meaning for mutations that are likely to have been present in Europeans before the ethnogenesis of present populations; subsequent population processes may have erased the traces of their geographic origin.

XV-2c/KM-19 haplotype analysis of cystic fibrosis mutations in Mexican patients

We analyzed 97 unrelated Mexican cystic fibrosis (CF) patients and their first-degree relatives to study the association of XV2C/TaqI/KM19/PstI haplotypes with CF mutations in this population. Haplotype phases could be established in 148 CF and 110 normal chromosomes, and haplotype distributions of normal and CF chromosomes differed significantly (P < 0.001). DeltaF508 and G542X mutations accounted for 56% of CF chromosomes and were found to be associated with haplotype B in 97.2% and 72.7% of chromosomes, respectively. The haplotype distribution of CF chromosomes carrying other rare and unknown mutations was similar to that of normal chromosomes (P > 0.05), haplotypes A and C being the most frequent. This is in accordance with the extensive heterogeneity and the spectrum of mutations reported in Mexican CF patients. We also report the haplotype distribution of all informative chromosomes bearing rare mutations; some were found to be associated with previously reported haplotypes, whereas others were found on different haplotypes. Recombination or recurrence of mutations may explain these different associations, although other intragenic markers must be used to better understand the origin and dispersion of CF mutations in our country. XK haplotype analysis allowed carrier detection among sibs in 24.3% of families, showing that this method may be useful for carrier detection in populations with high allelic heterogeneity.

Using linked markers to infer the age of a mutation

Advances in sequencing and genotyping technologies over the last decade have enabled geneticists to easily characterize genetic variation at the nucleotide level. Hundreds of genes harboring mutations associated with genetic disease have now been identified by positional cloning. Using variation at closely linked genetic markers, it is possible to predict the times in the past at which particular mutations arose. Such studies suggest that many of the rare mutations underlying human genetic disorders are relatively young. Studies of variation at genetic markers linked to particular mutations can provide insights into human geographic history, and historical patterns of natural selection and disease, that are not available from other sources. We review two approaches for estimating allele age using variation at linked genetic markers. A phylogenetic approach aims to reconstruct the gene tree underlying a sample of chromosomes carrying a particular mutation, obtaining a "direct" estimate of allele age from the age of the root of this tree. A population genetic approach relies on models of demography, mutation, and/or recombination to estimate allele age without explicitly reconstructing the gene tree. Phylogenetic methods are best suited for studies of ancient mutations, while population genetic methods are better suited for studies of recent mutations. Methods that rely on recombination to infer the ages of alleles can be fine-tuned by choosing linked markers at optimal map distances to maximize the information available about allele age. A limitation of methods that rely on recombination is the frequent lack of a fine-scale linkage map. Maximum likelihood and Bayesian methods for estimating allele age that rely on intensive numerical computation are described, as well as "composite" likelihood and moment-based methods that lead to simple estimators. The former provide more accurate estimates (particularly for large samples of chromosomes) and should be employed if computationally practical.

Geographic distribution and regional origin of 272 cystic fibrosis mutations in European populations. The Biomed CF Mutation Analysis Consortium

The geographic distribution of 272 cystic fibrosis (CF) mutations has been studied by assessing the origin of 27,177 CF chromosomes from 29 European countries and three countries from the North of Africa. The most common mutations are delta F308 (66.8%), G542X (2.6%), N1303K (1.6%), G551D (1.5%) and W1282X (1.0%). The delta F508 mutation has the highest frequency in Denmark (87.2%) and the lowest in Algeria (26.3%). Mutation G542X is common in the Mediterranean countries, with a mean frequency of 6.1%. N1303K is found in most of the western and Mediterranean countries and has the highest frequency in Tunisia (17.2%). The wide distribution of these mutations suggests an ancient origin. G551D is common in north-west and central Europe, but is uncommon in other parts of Europe. W1282X has the highest frequency in Israel (36.2%), being also common in most Mediterranean countries and north Africa. Seventeen mutation have frequencies between 0.1 and 0.9%, 1717-1G-->A (0.83%), R553X (0.75%), R1162X (0.51%), 621 + 1G-->T (0.54%) and 2183AA-->G (0.36%), being the most common ones. Some mutations reach relatively high frequencies in some extended geographic regions, such as mutation 394delTT in northern Europe (1.1-28.8%), R117H in northwestern Europe (1.3-3.0%), R553X in central Europe (1.1-24.4%), 1717-1G-->A in Belgium and France (1.1-5.3%), and 2183AA-->G in Italy and Greece (3.2%). Other mutations are only common in small regions: T338I (Sardinia), 711 + 1G-->T (Tunisia), R1162X (Algeria and north of Italy), 1609delCA (east of Spain), 1811 + 1.6kbA-->G (southeastern Spain), R1066C (Portugal), S549R (Algeria), R334W (Crete), 621 + 1G-->T (Central Greece), 3849 + 10kbC-->T (Israel), 2789 + 5G-->A (south of Greece), 451 + 1G--A (Israel), R347P (south of Bulgaria), 1677delTA (south of Bulgaria and Turkey), G85E (south of Greece), R347H (Turkey), 3905insT (Switzerland), 1078delT (Brittany), 1898 + 1G-->A (Wales), A455E (The Netherlands), delta I507 (Brittany), 3659delC (Sweden) and R560T (northern Ireland). Most of these mutations must have an origin and diffusion in the specific European population subgroup. Overall 55 mutations are common in one or several countries or regions of Europe and 217 mutations are rare with relative frequencies of lower than 1% in any of these regions and countries. This information might facilitate mutation analysis of CF in the different regions of Europe.

Identification of cystic fibrosis mutations in the United Arab Emirates. Mutations in brief no. 133. Online

We have designed a study aimed at identifying the genetic mutations responsible for cystic fibrosis (CF) in the population of the United Arab Emirates. The prevalence of CF in the UAE is at least 1/15,000 live births and the disease is associated with very severe clinical presentations. We have investigated 17 unrelated families. Ten UAE national families were of Bedouin descent: all 15 CF patients, who presented with very severe forms of the disease, were homozygous for a S549R mutation due to a T->G transversion at nucleotide postion 1779. Amongst a distinct population of Baluch origin, CF patients from 6 out of 7 affected families were DF508 homozyotes. Hence, the unique distribution of CF mutations in the United Arab Emirates--two mutations, S549R and DF508, characterize so far 94% of CF families--should allow efficient organizing and delivering of CF carrier screening programmes on the country's relatively limited population size.

Molecular basis of cystic fibrosis in the Republic of Macedonia

Eighty-three cystic fibrosis (CF) patients and their families, belonging to various ethnic groups living in the Republic of Macedonia were studied for molecular defects in the cystic fibrosis transmembrane conductance regulator (CFTR) gene, and for the associated extragenic marker loci XV-2c and KM19. The DNA methodology used included characterization of CFTR mutations in 19 exons (and flanking sequences) of the gene and analysis of distribution of the XV-2c/KM19 haplotypes among normal (N) and CF chromosomes by polymerase chain reaction (PCR) amplification followed by dot blot hybridization, restriction digestion, single-strand conformational polymorphism, constant denaturing gel electrophoresis, denaturing gradient gel electrophoresis, and sequencing. We identified 58.4% (97/166) of the CF chromosomes. Nine different CFTR gene mutations, including three novel ones, were found. Eight known and one new CFTR intragene polymorphisms were also characterized. The haplotype analysis of the XV-2c/TaqI and KM19/PstI polymorphic loci have shown that haplotype C is the most frequently found haplotype among the non-deltaF508 CF chromosomes from Macedonia (36.5%). The results demonstrate the broad heterogeneity of CF origin in this part of the Balkan Peninsula.

Costs, effects, and savings of screening for cystic fibrosis gene carriers

STUDY OBJECTIVE

Evaluating the costs, effects, and savings of several strategies for cystic fibrosis (CF) gene carrier screening.

DESIGN

A general model for evaluating prenatal, preconceptional, school, and neonatal carrier screening was constructed. For prenatal and preconceptional screening, two strategies were evaluated: single entry and double entry two step couple screening. Firstly, the Dutch situation was evaluated prospectively; subsequently the results were generalised to other carrier frequencies.

SETTING

Prospective simulation model.

MAIN RESULTS

Of all screening strategies, neonatal carrier screening gives most carrier couples an informed choice concerning reproduction. If the parents of carrier newborns would not be tested however, prenatal screening detects most carrier couples. Prenatal and single entry preconceptional screening programmes have a favourable cost-savings balance in the Netherlands under a wide range of assumptions. For double entry preconceptional screening and neonatal screening, high enough values of uptake of screening, prenatal diagnosis, and induced abortion are necessary. School carrier screening does not have a favourable cost-savings balance.

CONCLUSIONS

If a CF screening programme is judged to be useful on individual and social grounds, costs considerations are no obstacle for prenatal and single entry preconceptional screening.

A survey of the newborn populations in Belgium, Germany, Poland, Czech Republic, Hungary, Bulgaria, Spain, Turkey, and Japan for the G985 variant allele with haplotype analysis at the medium chain Acyl-CoA dehydrogenase gene locus: clinical and evolutionary consideration

Medium chain acyl-CoA dehydrogenase (MCAD) deficiency is an inborn error of fatty acid metabolism. It is one of the most frequent genetic metabolic disorders among Caucasian children. The G985 allele represented 90% of all the variant alleles of the MCAD gene in an extensive series of retrospective studies. To study the distribution of the G985 allele, newborn blood samples from the following countries were tested; 3000 from Germany (1/116). 1000 each from Belgium (1/77). Poland (1/98), Czech Republic (1/240). Hungary (1/168), Bulgaria (1/91), Spain (1/141). Turkey (1/216), and 500 from Japan (none). The frequency is shown in parentheses. The haplotype of G985 alleles in 1 homozygote and 57 heterozygote samples were then analyzed using two intragenic MCAD gene polymorphisms (Iaq1 and GT-repeat). The result indicated that only 1 of the 10 known haplotypes was associated with the G985 mutation, suggesting that G985 was derived originally from a single ancestral source. We made a compilation of the G985 frequencies in these countries and those in nine other European countries studied previously. The G985 distribution was high in the area stretching from Russia to Bulgaria in the east and in all northern countries in western and middle Europe, but low in the southern part of western and middle Europe. The incidence among ethnic Basques appeared to be low. This distribution pattern and the fact that all G985 alleles belong to a single haplotype suggest that G985 mutation occurred later than the delta F508 mutation of the CFTR, possibly in the neolithic or in a later period, and was brought into Europe by IndoEuropean-speaking people. The panEuropean distribution of the G985 allele, including Slavic countries from which patients with MCAD deficiency have rarely been detected, indicates the importance of raising the level of awareness of this disease.

Prenatal cystic fibrosis screening in a low-risk population undergoing chorionic villus sampling for fetal karyotyping

Screening for cystic fibrosis (CF) has been offered to pregnant women seeking chorionic villus sampling (CVS) for prenatal chromosomal abnormality investigation. The mutation panel has increased over the years to include 8 mutations and can detect 65% of abnormal CF genes in the Italian population. Testing was offered to a total of 2214 consecutive pregnant women; 45 of them declined screening (take up rate: 98%). In 1055 of the 2169 pregnancies screened, the test was at first done on the fetus, while in the remaining cases both parents were investigated. Among parents 46 carriers were identified (2.1%), in 41 of whom the mutation was delta F508. In two couples both parents were heterozygous, and in one the fetus was affected and the pregnancy was terminated. Although CF testing offered to pregnant women undergoing invasive investigation such as CVS may not be the model for a mass screening, its very high effectiveness can represent an advantageous component of more comprehensive strategies.

Prenatal diagnosis of cystic fibrosis in a highly heterogeneous population

Cystic fibrosis (CF) is the most common autosomal recessive disease in Caucasian populations. The Spanish CF population is highly heterogeneous, with more than 70 different mutations causing CF. Since the CFTR gene was cloned, we have performed 81 prenatal diagnoses for 74 couples. Sixty-nine cases had a high risk (1/4) for CF and 12 presented a lower risk (1/240). Direct analysis was possible in 36 cases (44.4 per cent); it was necessary to combine mutation analysis with polymorphic markers in 24 cases (29.6 per cent); mutation analysis and microvillar enzymatic (MVE) analysis were combined in five cases (6.1 per cent); and in 16 cases (19.8 per cent), only indirect analysis was possible. Nine different mutations were detected in this series of families: 621 + 1G -> T, delta F508, 1609delCA, G542X, G551D, 1949del84, R1162X, W1282X, and N1303K. Another ten mutations were identified in these samples after prenatal diagnosis (1811 + 1.6kbA -> G, 711 + 1G -> T, 2869insG, G85E, 2176insC, delta I507, 3272-26A -> G, Q890X, R1066C, and 4005 + 1G -> A). Our current strategy for molecular diagnosis of CF in the Spanish population is based, as a first step, on direct analysis for the two most frequent mutations (delta F508 and G542X) and indirect analysis using the intragenic markers IVS8CA, IVS17BTA, and IVS17BCA. The second step consists of screening for the mutations already associated with the CFTR microsatellite haplotypes. The third step is a specific search for unknown mutations. While actual diagnostic methods are not automatic and robust enough for heterogeneous populations, the diagnostic strategy outlined provides rapid, accurate, and reliable prenatal diagnosis for the majority of couples.

Mutation characterization of CFTR gene in 206 Northern Irish CF families: thirty mutations, including two novel, account for approximately 94% of CF chromosomes

A variety of mutation detection techniques, including restriction endonuclease digestion, allele specific oligonucleotides, and automated fluorescent sequencing, were used in the identification of 15 CFTR mutations representing 86.7% of CF chromosomes in 206 Northern Irish cystic fibrosis (CF) families. A systematic analysis of the 27 exons and intron/exon boundaries of the CFTR gene was performed using denaturing gradient gel electrophoresis (DGGE) in an attempt to characterise the 55 unknown CF mutations in 51 patients. Twenty different mutations were detected by DGGE on 30 chromosomes accounting for a further 7.3% of CF alleles. Fifteen of these mutations had not previously been found in Northern Ireland, and two are novel, M1I(G > T) and V562L. In total, 30 CFTR mutations account for 93.9% of the 412 Northern Irish CF chromosomes tested. The three major CF mutations in Northern Ireland are delta F508, G551D, and R117H with respective frequencies of 68.0%, 5.1%, and 4.1%. The efficacy of the DGGE technique was proven by the detection of 77 out of 77 control variants from all the CFTR exons. DGGE is a highly efficient and sensitive method for mutation screening especially in large genes where the mutation spectrum is known to be heterogeneous.

Search for mutations in pancreatic sufficient cystic fibrosis Italian patients: detection of 90% of molecular defects and identification of three novel mutations

A cohort of 31 cystic fibrosis patients showing pancreatic sufficiency and bearing an unidentified mutation on at least one chromosome was analyzed through denaturing gradient gel electrophoresis of the whole coding region of the cystic fibrosis transmembrane conductance regulator gene, including intron-exon boundaries. Three new and 19 previously described mutations were detected. The combination of these with known mutations detected by other methods, allowed the characterization of mutations on 56/62 (90.3%) chromosomes. Among those identified, 17 can be considered responsible for pancreatic sufficiency, since they were found in patients carrying a severe mutation on the other chromosome. Among these presumed mild mutations, eight were detected more than once, R352Q being the most frequent in this sample (4.83%). Intragenic microsatellite analysis revealed that the six chromosomes still bearing unidentified mutations are associated with five different haplotypes. This may indicate that these chromosomes bear different mutations, rarely occurring among cystic fibrosis patients, further underlying the molecular heterogeneity of the genetic defects present in patients having pancreatic sufficiency.

High incidence of cystic fibrosis on the Faroe Islands: a molecular and genealogical study

We have studied the genetics of cystic fibrosis (CF) in The Faroe Islands. Based on the number of affected children born during the period 1954-1993, the incidence of CF at birth is 1:1775, which is more than twice the incidence in the rest of Denmark. We have tested all known CF patients and/or their parents for the presence of delta F508 and found it to be the only CF mutation in this population. Based on testing 881 unrelated control individuals, the carrier frequency was estimated to be 1:24, given a calculated incidence of 1:2300. Genealogical studies enabled us to trace several of the families over seven generations. Haplotype investigations within the families suggest that delta F508 was introduced by two founders, probably from the Celtic population in Brittany, Ireland, Wales or the North West of Scotland.

Mutation analysis of Western Australian families affected by cystic fibrosis

OBJECTIVE

To document the results of mutation analysis on 160 individuals with cystic fibrosis and 31 obligate carriers of the cystic fibrosis gene in 191 Western Australian families to facilitate accurate genetic counselling.

METHODS

We tested for 17 mutations of the cystic fibrosis gene by either a variation of the polymerase chain reaction amplification refractory mutation system (PCR-ARMS) or with a series of restriction enzyme cuts and dot blots using chemiluminescent probes.

RESULTS

At least one of the two intragenic mutations causing cystic fibrosis was identified in 98% of affected individuals and both were detected in 68%. The delta F508 deletion occurred in 89.8% of patients: 51% were homozygous for this defect. In carriers, 85% of the mutations were detected with a panel of 16 probes, identifying 17 intragenic defects: the delta F508 deletion occurred in 72.4%. Both cystic fibrosis mutations were detected in 68% of cystic fibrosis families.

CONCLUSIONS

By analysis with 16 intragenic cystic fibrosis genomic probes, we have documented the frequencies of various mutations in the Western Australian population. These data will be useful in accurate genetic counselling for affected families and carrier screening for the general population.

Analysis of linkage disequilibrium between different cystic fibrosis mutations and three intragenic microsatellites in the Italian population

Three intragenic microsatellites of the CFTR gene, a TA and a CA repeats, namely IVS17bTA and IVS17bCA, located in intron 17b and a CA repeat (IVS8CA) located in intron 8 of the CFTR gene, were analyzed in a large sample of Italian cystic fibrosis (CF) and normal chromosomes. Linkage disequilibrium was evaluated between each marker and difference CF mutations on a total of 377 CF and 358 normal chromosomes. Our results are consistent with the hypothesis that all delta F508 chromosomes derive from a single mutational event. The same hypothesis is valid for mutations G542X, N1303K, 1717-1G-->A, which might have been originated more recently than delta F508.

Analysis of 40 known cystic fibrosis mutations in South African patients

A total of 140 South African (SA) Caucasoid cystic fibrosis (CF) families were analysed for the common CF mutation, delta F508. The 52 non-delta F508 CF chromosomes in a subset of 127 of these families were also tested for 39 other known CF mutations. The most frequent mutation, apart from delta F508 (which occurs at a frequency of 79%), was G542X (1.3%). Four other mutations, R553X, S549N, 621 + 1G-->T and N1303K, were each found in single families. The other 35 mutations remained unidentified in this sample of CF families. Since 83% of SA Caucasoid CF mutations have been identified, diagnosis by mutation analysis will be possible in only 69% of CF cases. When a diagnosis has been confirmed by a positive sweat test, a combination of linked marker analysis and mutation detection will be necessary if prenatal diagnosis and carrier detection are to be offered in the remaining families.

Molecular and clinical analyses of cystic fibrosis in the south of Spain

We report molecular and clinical analyses in 71 unrelated patients with cystic fibrosis (CF) from Andalusia (South of Spain). Direct mutation analysis of six mutations of the CFTR gene (delta F508, G542X, R1162X, N1303K, W1182X and 1949de184) was performed. The proportion of CF chromosomes with the above-mentioned mutations was 58.5%. Haplotype analysis was performed with the marker/enzyme pairs XV2C/TaqI and KM19/PstI. A particular haplotype has been found associated with each of the studied mutations, while the pooled data for the unknown mutations are not associated with any particular haplotype. This lack of association indicates that there will not be a single predominant mutation amongst the other CF chromosomes. To assess the relationship between genotype and phenotype in these patients, we correlated the pancreatic status and the occurrence of chronic Pseudomona aeruginosa infection with the observed genotype. Pancreatic insufficiency was present in all patients in whom the analyzed mutations were found to be homozygous or compound heterozygous. We also found a higher rate of Pseudomonas colonization in the group of patients in whom the genotype was homozygous or compound heterozygous for the analysed mutations when compared with the group of patients with a different genotype, but the difference was not statistically significant.

Arylsulfatase A pseudodeficiency: a common polymorphism which is associated with a unique haplotype

The allele for pseudodeficiency (PD) of the lysosomal enzyme arylsulfatase A (ARSA) is a common polymorphism in all populations. The PD allele frequency in different Israeli ethnic groups was found to range from 9.2-22.7%. The PD allele includes two different mutations PD(1) and PD(2) in an approximately 1 Kb interval. In this study we confirmed that while PD(1) may be found alone as a polymorphism, PD(2) is always associated with the PD allele (660 alleles screened). Analysis of three ARSA intragenic polymorphisms showed a complete linkage disequilibrium between the PD allele and an haplotype defined by the three polymorphic restriction sites. The results suggest that the origin of the PD polymorphism may be a common founder, or recurrent mutations which are occurring in a unique haplotype.

The origin of the major cystic fibrosis mutation (delta F508) in European populations

delta F508 is the most frequent cystic fibrosis (CF) mutation and accounts for approximately 70% of CF chromosomes worldwide. Three highly polymorphic microsatellite markers have been used to study the origin and evolution of delta F508 chromosomes in Europe. Haplotype data demonstrate that delta F508 occurred more than 52,000 years ago, in a population genetically distinct from any present European group, and spread throughout Europe in chronologically distinct expansions, which are responsible for the different frequencies of delta F508 in Europe.

Informativity of intragenic microsatellites for carrier detection and prenatal diagnosis of cystic fibrosis in the Italian population

Molecular diagnosis of cystic fibrosis (CF) in the Italian population, based on the detection of the deltaF508 mutation (51.2% of CF chromosomes), provides full informativity for prenatal diagnosis (PDN) in about 28% of families at risk. Identification of the predominant non-deltaF508 mutations allows the characterization of about 70% of CF chromosomes, making approximately 48% of couples fully informative. In families where at least one chromosome remains uncharacterized, allele segregation is still determined using RFLPs closely linked to the CF gene. The recent identification of three polymorphic clusters of dinucleotide repeats (IVS8/GT, IVS17b/TA and IVS17b/CA) led us to evaluate whether their analysis might improve feasibility studies for prenatal diagnosis or heterozygote identification. One hundred nuclear families with a CF child, reflecting the general Italian deltaF508 mutation distribution, were genotyped for the three microsatellites. In this study microsatellite analysis using IVS8/GT and IVS17b/TA allowed the identification of both parental CF chromosomes in 94% of couples; inclusion in the study of the less polymorphic repeat locus, IVS17b/CA, slightly improved this percentage (97%). Hence, a strategy involving primarily the detection of the deltaF508 mutation and secondarily microsatellite analysis makes possible PDN of CF in virtually all Italian CF families.

Mutation analysis in the diagnosis of cystic fibrosis

Since the characterization of the gene encoding the cystic fibrosis transmembrane conductance regulator protein and identification of its main mutation, delta F508, causing cystic fibrosis (CF), more than 150 mutations in this gene have been reported, most of them only in a few or even single CF patients. Attempts to use mutation analysis in genetic counselling or for the diagnosis of CF depends on prevalence data of certain mutations in the respective population, and considerable ethnic differences have been reported. In this study we determined the prevalence of the mutations delta F508, G551D, R553X, and G542X and of genotypes defined by these mutations in 239 CF patients (444 independent CF chromosomes) seen in our clinic. The analysis for those four mutations alone now permits identification of approximately 75% of all mutations in our CF patients. The complete genotype can be resolved in approximately 63% of patients. This represents the diagnostic sensitivity which can be achieved by mutation analysis in patients without a family history of CF. We conclude that in situations where conventional diagnostic tests are not feasible or difficult to interpret, mutation analysis using a limited set of mutations can contribute significantly to an early and specific diagnosis of CF.

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

The major cystic fibrosis (CF) mutation, delta F508, is associated with one haplotype (B) determined by the two polymorphic markers, XV2C and KM19. This haplotype is rare (15%) among non-CF chromosomes. Its frequency among non-delta 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 200 kb 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-delta F508 CF chromosomes associated with haplotype B was 70% (88% among Ashkenazi CF chromosomes). Nine mutations (delta F508, W1282X, G542X, N1303K, 3849 + 10 kb C-->T, Q359K/T360K, S549I, S549R, and 1717-1G-->A) 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 (delta F508, W1282X, G542X, N1303K, Q359K/T360K, S549R, and 1717-1G-->A). 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 1717-1G-->A, 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.

Prevalence of cystic fibrosis mutations in the Grampian region of Scotland

We have identified all known sufferers of cystic fibrosis (CF) alive in the Grampian region, north east Scotland, on 1 January 1989. DNA samples were obtained for a prevalence study of the common mutations with near to complete ascertainment. A relatively high prevalence of the delta F508 mutation was found (82%), with one of four mutations being present on 92% of CF chromosomes. The high prevalence of these four easily detectable mutations in Grampian has local implications for genetic counselling, the efficacy of population carrier screening, and the usefulness of mutation analysis in cases where the diagnosis of CF is in doubt.

Absence of cystic fibrosis mutations in a large Asian population sample and occurrence of a homozygous S549N mutation in an inbred Pakistani family

The occurrence of cystic fibrosis is very rare in the Asian population. Carriers of the mutations most commonly found in Caucasians were not detected in a large Asian population sample of almost 900 chromosomes. However, an affected Pakistani child born to consanguineous parents was further investigated and shown to be homozygous for the mutation S549N (G-->A). Molecular and clinical data are presented which may improve our understanding of the phenotypic effects of the S549N mutation in the CFTR gene.

Spectrum of mutations in cystic fibrosis

Cystic fibrosis (CF) is a disorder characterized by elevated sweat electrolytes and thick mucous secretions due to abnormal chloride permeability in epithelial tissues. The gene responsible for this disease, the CF transmembrane conductance regulator (CFTR) was identified by a positional cloning approach 3 years ago. Since that time, over two hundred mutations have been found in CFTR genes from affected individuals. Analysis of these disease-associated mutations has provided new insight into the etiology of this disease and into the mechanisms of epithelial electrolyte secretion.

Psychological and social consequences of community carrier screening programme for cystic fibrosis

We have assessed the effect of screening for cystic fibrosis (CF) carrier status on anxiety levels, attitudes, knowledge and actions of participants in a pilot programme conducted through primary health care services. Over 3000 individuals were screened and 100 carriers with no previous family history were identified. Varying degrees of anxiety were found to be associated initially with a positive result, but most of this was allayed by genetic counselling, and we find no adverse long-term psychological consequences in carriers. Most discussed carrier status with their partner (89%), parents, other relatives and also with friends; 87% of partners to whom testing was suggested have been screened. Those testing positive indicated that knowledge of carrier status would be considered in future reproductive decisions, and after 6 months carriers retained a reasonable level of knowledge about CF and its inheritance. Carriers and non-carriers uniformly approve of screening and are glad to have been tested. Knowledge of CF in the sample of non-carriers has also increased after testing, suggesting screening may improve understanding of CF among the entire target population. Fears of possible social costs of screening may be ill-founded.