CFTR Haplotype Analysis Reveals Genetic Heterogeneity in the Etiology of Congenital Bilateral Aplasia of the Vas Deferens

Congenital bilateral aplasia of the vas deferens (CBAVD) was suggested to be a mild form of cystic fibrosis (CF). Mutation analysis of the cystic fibrosis transmembrane conductance regulator (CFTR) gene in males with CBAVD revealed that in some males CBAVD is caused by two defective CFTR alleles. The genetic basis of CBAVD in the other males and its association with CF remained unclear. We undertook this study to test the hypothesis of commonality of CBAVD and CF by haplotype analysis, in the CFTR locus, of males suffering from CBAVD and of their families. According to the hypothesis of commonality of CBAVD and CF, two brothers with CBAVD are expected to carry the same two CFTR alleles, while their fertile brothers are expected to carry at least one different allele. Eleven families were studied, of which two families, with unidentified CFTR mutations, did not support this hypothesis. In these families two brothers with CBAVD inherited different CFTR alleles. Their fertile brothers inherited the same CFTR alleles as their brothers with CBAVD. These results provide evidence for genetic heterogeneity in CBAVD. Though in some families CBAVD is associated with two CFTR mutations, we suggest that in others it is caused by other mechanisms, such as mutations at other loci or homozygosity or heterozygosity for partially penetrant CFTR mutations.     

Cystic fibrosis as a cause of infertility

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

Gène CFTR et infertilité masculine en 2001 Conseil génétique, diagnostic prénatal, diagnostic pré-implantatoire

As the vas deferens is also absent in the majority of CF (cystic fibrosis) males, it has been proposed that CBAVD (Congenital Bilateral Absence of Vas Deferens) males may present an incomplete or mild form of CF. Many studies using more extensive mutation analysis have confirmed the role of CFTR gene defects: 80% of CBAVD patients carry one or two mutations. Each patient with a diagnosis of CBAVD should also be examined for pulmonary and pancreatic signs, and sweat tests should be performed. In couples with CBAVD linked to CFTR mutations, the risk of having children with CF or infertility is increased if the female is also a carrier. The woman should be screened for the most frequent CFTR mutations according to her ethnic background. After screening for 80% of the mutations responsible for CF, the residual risk of being a carrier with negative screening is: Z=h(1?a)/(1?ah)=1/120 considering a carrier frequency of 1/25 in the general population. In the case of positive screening, antenatal diagnosis by chorionic villus sampling may be proposed. However, in some situations it is difficult to predict the phenotypic consequences for the child, particularly when a severe transmutation of a variable allele is identified. As these couples require medically-assisted reproduction techniques, pre-implantation genetic diagnosis appears to be more appropriate than antenatal diagnosis. Only embryos that inherit the non-mutated maternal CFTR allele are replaced in the uterus. Examination of childre born to couples with CBAVD is mandatory: immunoreactive trypsinogen assay at 3 days of age, sweat test at 3 months and clinical examination, especially looking for signs of CF. Identification of CFTR mutations in a CBAVD patient has important consequences for his family. Each sibling has a 50% risk of being a carrier and a 25% risk of inheriting the same genotype. The genetic counsellor must inform these siblings about the possible risk of having CF children if they carry CFTR mutations and if their partner is also a carrier.     

Increased frequency of CFTR gene mutations identified in Indian infertile men with non-CBAVD obstructive azoospermia and spermatogenic failure

High incidence of mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene is associated with congenital bilateral absence of the vas deferens (CBAVD) and is considered as the genital form of cystic fibrosis (CF). The CFTR gene may also be involved in the etiology of male infertility in cases other than CBAVD. The present study was conducted to identify the spectrum and frequency of CFTR gene mutations in infertile Indian males with non-CBAVD obstructive azoospermia (n = 60) and spermatogenic failure (n = 150). Conspicuously higher frequency of heterozygote F508del mutation was detected in infertile males with non-CBAVD obstructive azoospermia (11.6%) and spermatogenic failure (7.3%). Homozygous IVS(8)-5T allele frequency was also significantly higher in both groups in comparison to those in normal healthy individuals. Two mutations in exon 25 viz., R1358I and K1351R were identified as novel mutations in patients with non-CBAVD obstructive azoospermia. Mutation R1358I was predicted as probably damaging CFTR mutation. This is the first report from the Indian population, emphasizing increased frequency of CFTR gene mutations in male infertility other than CBAVD. Thus, it is suggested that screening of CFTR gene mutations may be required in infertile Indian males with other forms of infertility apart from CBAVD and willing for assisted reproduction technology.     

Extensive analysis of 40 infertile patients with congenital absence of the vas deferens: in 50% of cases only one CFTR allele could be detected

Mutations in the cystic fibrosis (CF) conductance transmembrane regulator (CFTR) gene have been detected in patients with CF and in males with infertility attributable to congenital bilateral absence of the vas deferens (CBAVD). Thirty individuals with CBAVD and 10 with congenital unilateral absence of the vas deferens (CUAVD) were analyzed by single-strand conformation analysis and denaturing gradient gel electrophoresis for mutations in most of the CFTR gene. All 40 individuals were pancreatic sufficient, but twenty patients had recurrent or sporadic respiratory infections, asthma/asthmatic bronchitis, and/or rhino-sinusitis. Agenesia or displasia of one or both seminal vesicles was detected in 30 men and other urogenital malformations were present in six subjects. Among the 40 samples, we identified 13 different CFTR mutations, two of which were previously unknown. One new mutation in exon 4 was the deletion of glutamic acid at codon 115 (E115). A second new mutation was found in exon 17b, viz., an AC substitution at position 3311, changing lysine to threonine at codon 1060 (K1060T). CFTR mutations were detected in 22 out of 30 (73.3%) CBAVD patients and in one out of 10 (10%) CUAVD individuals, showing a significantly lower incidence of CFTR mutations in CBAVD/CUAVD patients (P 0.0001), compared with that found in the CF patient population. Only three CBAVD patients were found with more than one CFTR mutation (F508/L206W, F508/R74W+D1270N, Rl 17H/712-1GT), highlighting L206W, R74W/ D1270N, and R117H as benign CF mutations. Sweat electrolyte values were increased in 76.6% of CBAVD patients, but three individuals without CFTR mutations had normal sweat electrolyte levels (10% of the total CBAVD patients), suggesting that factors other than CFTR mutations are involved in CBAVD. The failure to identify a second mutation in exons and their flanking regions of the CFTR gene suggests that these mutations could be located in introns or in the promoter region of CFTR. Such mutations could result in CFTR levels below the minimum 6%–10% necessary for normal protein function.     

Is congenital bilateral absence of vas deferens a primary form of cystic fibrosis? Analyses of the CFTR gene in 67 patients.

Congenital bilateral absence of the vas deferens (CBAVD) is an important cause of sterility in men. Although the genetic basis of this condition is still unclear, it has been shown recently that some of these patients carry mutations in their cystic fibrosis transmembrane conductance regulator (CFTR) genes. To extend this observation, we have analyzed the entire coding sequence of the CFTR gene in a cohort of 67 men with CBAVD, who are otherwise healthy. We have identified four novel missense mutations (A800G, G149R, R258G, and E193K). We have shown that 42% of subjects were carriers of one CFTR allele and that 24% are compound heterozygous for CFTR alleles. Thus, we have been unable to identify 76% of these patients as carrying two CFTR mutations. Furthermore, we have described the segregation of CFTR haplotypes in the family of one CBAVD male; in this family are two male siblings, with identical CFTR loci but displaying different phenotypes, one of them being fertile and the other sterile. The data presented in this family, indicating a discordance between the CBAVD phenotype and a marked carrier (delta F508) chromosome, support the involvement of another gene(s), in the etiology of CBAVD.     

Les génotypes responsables de mucoviscidose ou d’absence bilatérale des canaux déférents ABCD

Over the last decade, the genetic basis for CBAVD has been identified by its association with CFTR gene mutations, and CBAVD is now generally considered to be a mild or incomplete form of CF. In this review, the author summarizes the main results of compilation of CFTR gene analysis conducted in French laboratories for 3,923 patients with CF and 800 males with CABVD. The degree of clinical expression can be affected by several variables, including the molecular mechanisms by which the various CFTR mutations impair or disrupt the function of the CFTR chloride channel. Phenotypic expression of CFTR mutational genotypes varies from severe, progressive pulmonary disease with pancreatic insufficiency (CF-PI), to mild pulmonary disease with pancreatic sufficiency (PS) or singleorgan forms of “CFTR-opathies”. In CF, a total of 310 different CFTR mutations accounting for 94% of 7,846 CF alleles have generated almost 500 different genotypes, comprising 2 severe mutations in 88% of cases (CF-PI), one severe mutation in trans to a mild mutation in 11% (CF-PS), and 2 mild mutations in 1% of identified genotypes. In CBAVD, 137 mutations scattered over the whole gene were identified in 60% of 1,600 CBAVD alleles during the study. Among the 150 characterized mutational CFTR genotypes, compound heterozygosity was the rule, and the most frequent CBAVD combinations were ΔF508/5T (35%), ΔF508/other mutation (30%, including ΔF508/R117H-7T: 5,6%), and 5T/other mutation (17%). No combination of two severe mutations was found in CBAVD (0%); by contrast with the CF population, 88% of genotypes identified in CBAVD comprised a severe mutation in trans to a mild mutation, and 12% consisted of 2 mild mutations. A total of 22 genotypes were shared by both CF and CBAVD. The role of the 5T allele as a splicing variant with variable, incomplete disease penetrance in CBAVD is reviewed. Other haplotype backgrounds, such as the TG12 sequence and the M470V polymorphism, may influence CFTR splicing and/or function. This study confirms the high molecular heterogeneity of CFTR mutations in CBAVD and emphasizes the importance of extensive CFTR analysis in these patients. Longterm follow-up studies of CBAVD patients are necessary in order to predict the phenotypic consequences of numerous CFTR mutational genotypes.     

Mukoviszidose – eine pleiotrope Ionenkanalerkrankung mit wesentlicher Lungenbeteiligung

The monogenic disease cystic fibrosis is caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene and is inherited in an autosomal recessive fashion. Successful diagnosis of the disease is achieved by patient history, clinical assessment, genetic analysis of the CFTR gene and by in vivo measurement and ex vivo characterization of the basic defect in patient’s samples. Frequently, differential diagnosis of CFTR-related disorders such as congenital bilateral absence of the vas deferens (CBAVD), pancreatitis and bronchiectasis needs to be performed. Molecular therapeutics has been developed for some CFTR mutations and these will facilitate direct clinical use of the information provided by CFTR mutation analysis.     

Implication of the Cystic Fibrosis Transmembrane Conductance Regulator Gene in Infertile Family Members of Indian CF Patients

Cystic fibrosis (CF) is an autosomal recessive disease caused by mutations in the CFTR gene. Among males with CF, 95% are infertile due to congenital absence of the vas deferens. We investigated the role of family history of infertility among CF subjects and characterized mutations in them. Among 50 CF subjects, four had a family history of infertility. A homozygous c.1521_1523delCTT mutation was detected in one, two had a compound heterozygous genotype (c.1521_1523delCTT/c.3717 + 10 kbC>T), and c.1521_1523delCTT mutation was identified on one allele of fourth CF subject. Genetic analysis of each infertile family members of CF subjects revealed the c.1521_1523delCTT mutation on one allele; however, no mutation could be identified on other allele. Haplotype analysis of the infertile family members showed that at least one of the alleles shared the same haplotype as that of the index case. It is suggested that the CFTR gene is implicated in the infertile members of the CF families. Failure to detect mutations on the other allele by SSCP analysis demands direct gene sequencing to detect mutations in the intronic or promoter region.     

Congenital bilateral absence of the vas deferens (CBAVD) and cystic fibrosis transmembrane regulator (CFTR): correlation between genotype and phenotype

To assess better the link between congenital bilateral absence of the vas deferens (CBAVD) and cystic fibrosis (CF), we compared sweat chloride values, analysis of the CFTR intron 8 poly(T) tract length and analysis of 10 exons in a population of 38 patients with CBAVD. The data indicate that this population can be divided into three groups of patients. In the first group of 15 patients with abnormal sweat chloride (> 60 mmol/l), the frequency of CF mutations is high. In the second group of 18 patients with equivocal sweat chloride (between 40 and 60 mmol/l), the frequency of the 5T variant is high; 6 patients have a F508 mutation and a 5T variant and 1 patient is homozygous for the 5T variant; a 5T variant has been detected in 3 other patients, and a F508 mutation in another patient. A third group of 5 patients is probably not related to CF: these patients have other congenital abnormalities of the urogenital tract, low chloride values (< 40 mmol/l) and apparently no abnormality of the CF gene.     

Absence de corrélation génotype-phénotype dans les absences de canaux déférents

Absence of the vas deferens is a rare cause of male infertility, associated with mutations in the cystic fibrosis transmembrane regulator (CFTR) gene in about 80% of cases. Only limited published data are available concerning the correlation between genotype and reproductive tract abnormalities observed in this disease: presence or absence of seminal vesicles and parts of the epididymis, symmetrical or asymmetrical lesions, testicular volumes. We screened 47 patients for the 13 most common CFTR mutations on the cystic fibrosis gene and for the 5-thymidine variant of the polythymidine tract of intron 8. Renal, scrotal and transrectal ultrasonography was performed in each patient to explore the testes and reproductive tract. All patients presented absence of the ampullae of the vas deferens. Forty patients presented bilateral absence of the vas deferens and 7 presented unilateral absence of the vas deferens. At least one mutation of the cystic fibrosis gene was present in 64% of cases: 47% had the ΔF 508 mutation and 63% had the 5T allele. No mutation was detected in seventeen patients, including 3 patients with unilateral renal agenesis and 3 patients with unilateral absence of the vas deferens. No differences were observed for seminal vesicles and symmetry of vesicular and epididymal abnormalities between patients with or without CFTR gene mutations, but epididymal abnormalities were significantly more frequent in the group without mutation (p=0.01). Testicular volumes were significantly lower in the patients without mutation or with the 5T allele only, than in the patients with at least one CFTR gene mutation: 10.7±4.1 ml versus 15.1±4.5 ml, respectively (p<0.001). In conclusion, in cases of isolated absence of the vas deferens, there is no difference in sperm duct abnormalities between patients with or without CFTR gene mutation. These results suggest that other genetic or environmental determinants are required to explain a common pathogenesis for these malformations. The decreased testicular volume of patients without CFTR gene mutation or with the 5T allele only suggests the existence of an unidentified secretory or mixed factor involved in these forms of absence of the vas deferens.     

Effects of cystic fibrosis and congenital bilateral absence of the vas deferens-associated mutations on cystic fibrosis transmembrane conductance regulator-mediated regulation of separate channels

The protein defective in cystic fibrosis (CF), the CF transmembrane-conductance regulator (CFTR), functions as an epithelial chloride channel and as a regulator of separate ion channels. Although the consequences that disease-causing mutations have on the chloride-channel function have been studied extensively, little is known about the effects that mutations have on the regulatory function. To address this issue, we transiently expressed CFTR-bearing mutations associated with CF or its milder phenotype, congenital bilateral absence of the vas deferens, and determined whether mutant CFTR could regulate outwardly rectifying chloride channels (ORCCs). CFTR bearing a CF-associated mutation in the first nucleotide-binding domain (NBD1), DeltaF508, functioned as a chloride channel but did not regulate ORCCs. However, CFTR bearing disease-associated mutations in other domains retained both functions, regardless of the associated phenotype. Thus, a relationship between loss of CFTR regulatory function and disease severity is evident for NBD1, a region of CFTR that appears important for regulation of separate channels.     

Swine models of cystic fibrosis reveal male reproductive tract phenotype at birth

Nearly all male cystic fibrosis (CF) patients exhibit tissue abnormalities in the reproductive tract, a condition that renders them azoospermic and infertile. Two swine CF models have been reported recently that include respiratory and digestive manifestations that are comparable to human CF. The goal of this study was to determine the phenotypic changes that may be present in the vas deferens of these swine CF models. Tracts from CFTR(-/-) and CFTR(ΔF508/ΔF508) neonates revealed partial or total vas deferens and/or epididymis atresia at birth, while wild-type littermates were normal. Histopathological analysis revealed a range of tissue abnormalities and disruptions in tubular organization. Vas deferens epithelial cells were isolated and electrophysiological results support that CFTR(-/-) monolayers can exhibit Na(+) reabsorption but reveal no anion secretion following exposure to cAMP-generating compounds, suggesting that CFTR-dependent Cl(-) and/or HCO(3)(-) transport is completely impaired. SLC26A3 and SLC26A6 immunoreactivities were detected in all experimental groups, indicating that these two chloride-bicarbonate exchangers were present, but were either unable to function or their activity is electroneutral. In addition, no signs of increased mucus synthesis and/or secretion were present in the male excurrent ducts of these CF models. Results demonstrate a causal link between CFTR mutations and duct abnormalities that are manifested at birth.     

Heterogeneity in the severity of cystic fibrosis and the role of CFTR gene mutations

Cystic fibrosis is a common, fatal disorder caused by abnormalities in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. CFTR encodes a chloride channel that regulates secretion in many exocrine tissues. The presentation of cystic fibrosis is highly variable as measured by the age of onset of disease, the presence of pancreatic insufficiency, or the progression of lung disease. Over 400 mutations in the CFTR gene have been described in cystic fibrosis patients and considerable effort has focused on the correlation between specific mutations and genotypes and clinical characteristics. Individual tissues display variation in their sensitivity to CFTR mutations. The vas deferens is functionally disrupted in nearly all males, whereas mild and severe pancreatic involvement is determined by the patient's genotype. The severity of pulmonary disease is poorly correlated with genotype, suggesting that there are other important genetic and/or environmental factors that contribute to lung infections and the subsequent disruption of lung function.     

Spectrum of CFTR mutations in Mexican cystic fibrosis patients: identification of five novel mutations (W1098C, 846delT, P750L, 4160insGGGG and 297–1G→A)

We have analyzed 97 CF unrelated Mexican families for mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. Our initial screening for 12 selected CFTR mutations led to mutation detection in 56.66% of the tested chromosomes. In patients with at least one unknown mutation after preliminary screening, an extensive analysis of the CFTR gene by single stranded conformation polymorphism (SSCP) or by multiplex heteroduplex (mHET) analysis was performed. A total of 34 different mutations representing 74.58% of the CF chromosomes were identified, including five novel CFTR mutations: W1098C, P750L, 846delT, 4160insGGGG and 297-1G-->A. The level of detection of the CF mutations in Mexico is still lower than that observed in other populations with a relatively low frequency of the deltaF508 mutation, mainly from southern Europe. The CFTR gene analysis described here clearly demonstrated the high heterogeneity of our CF population, which could be explained by the complex ethnic composition of the Mexican population, in particular by the strong impact of the genetic pool from southern European countries.     

Morphological changes in the vas deferens and expression of the cystic fibrosis transmembrane conductance regulator (CFTR) in control, deltaF508 and knock-out CFTR mice during postnatal life

The morphology of the mouse vas deferens still undergoes major changes from birth to 40 days of age, such as differentiation of the mesenchymal cells into fibroblasts and muscle cells, differentiation of the epithelium into basal and columnar epithelial cells, development of stereocilia, and the appearance of smooth endoplasmic reticulum organised in fingerprint-like structures or parallel, flattened saccules. In mutant homozygous DeltaF508 (DeltaF/DeltaF) and knock-out (cf/cf) CFTR mice, strain 129/FvB and 129/C57BL-6, respectively, a similar development occurred until the age of 20 days. At 40 days, however, the lumen was filled with eosinophilic secretions, and sperm cells were absent in the majority of the animals examined, although sperm production in testis and epididymis appeared to be normal. CFTR was localised in the apical membrane and cytoplasm of the vas deferens epithelium from 40 days on but could not be detected in the vas deferens before 20 days or in mutant adult CFTR mice as expected. Western blots of membrane preparations showed that the mature form of CFTR was present in vas deferens and testis but absent in seminal vesicles. Our results suggest that the function of CFTR is probably essential after 20 days in the vas deferens and that its absence or dysfunction may result in a vas deferens with a differentiated epithelium but a collapsed lumen, which could at least temporarily delay the transport of spermatozoa. These observations contrast with those made in the overall majority of CF patients. Mol. Reprod. Dev. 55:125-135, 2000.     

'CFTR-opathies': disease phenotypes associated with cystic fibrosis transmembrane regulator gene mutations

Cystic fibrosis is a genetic disease that is associated with abnormal sweat electrolytes, sino-pulmonary disease, exocrine pancreatic insufficiency, and male infertility. Insights into genotype/phenotype relations have recently been gained in this disorder. The strongest relationship exists between 'severe' mutations in the gene that encodes the cystic fibrosis transmembrane regulator (CFTR) and pancreatic insufficiency. The relationship between 'mild' mutations, associated with residual CFTR function, and expression of disease is less precise. Atypical 'mild' mutations in the CFTR gene have been linked to late-onset pulmonary disease, congenital bilateral absence of the vas deferens, and idiopathic pancreatitis. Less commonly, sinusitis, allergic bronchopulmonary aspergillosis, and possibly even asthma may also be associated with mutations in the CFTR gene, but those syndromes predominantly reflect non-CFTR gene modifiers and environmental influences.     

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.