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

Structure-function analysis of a double-mutant cystic fibrosis transmembrane conductance regulator protein occurring in disorders related to cystic fibrosis

A number of disorders related to cystic fibrosis have been described since the cloning of the cystic fibrosis gene, including infertility due to the congenital bilateral absence of the vas deferens. We have identified, in several patients, complex cystic fibrosis transmembrane conductance regulator genotypes like double-mutant alleles. We have now analyzed the structure-function relationships of one of these mutants, R74W-D1270N cystic fibrosis transmembrane conductance regulator, expressed in HeLa cells, to evaluate the contribution of each mutation in the phenotype. We found that R74W cystic fibrosis transmembrane conductance regulator appears to be a polymorphism, while D1270N cystic fibrosis transmembrane conductance regulator could be responsible for the congenital bilateral absence of the vas deferens phenotype. The combination of the two produced a more severe effect on the chloride conductance pathway as well as on the phenotype.

Genetic diseases of the seminal ducts

Azoospermia due to an obstruction of the genital tract is one of numerous possible pathophysiologic mechanisms underlying male infertility. The blockage of the seminal ducts may be acquired or congenital. Only recently has the strong association between mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene and various subtypes of obstructive azoospermia been elucidated. Most patients with congenital bilateral absence of the vas deferens or bilateral ejaculatory duct obstruction are carriers of such mutations. The relationship between abnormal CFTR alleles and unilateral absence of the vas deferens, isolated seminal vesicle anomalies, and Young syndrome is less well characterized and awaits further investigation.

Nasal potential difference in congenital bilateral absence of the vas deferens

Congenital bilateral absence of the vas deferens (CBAVD) is supposed to be due to defective activity of the cystic fibrosis (CF) transmembrane conductance regulator (CFTR) in the genital tract. With the aim of studying CFTR activity in vivo we measured nasal potential difference (NPD) in a group of CBAVD subjects, who were then compared with normal control subjects and CF patients. Sodium transport, measured under basal conditions and after amiloride superinfusion, was normal in almost all CBAVD patients, who had NPD values similar to those of normal control subjects. Chloride transport was studied by measuring NPD during perfusion with a chloride-free solution and isoproterenol. Under these circumstances CBAVD patients as a whole showed normal chloride secretion. However, three subjects with CBAVD had abnormal NPD values. They had either elevated sweat chloride concentrations together with symptoms of mild CF, or compound heterozygosity (DeltaF508/R117H). In conclusion the group of CBAVD patients as a whole presented normal bioelectric properties of nasal epithelium, suggesting normal CFTR activity. In a small subgroup NPD was abnormal, suggesting a diagnosis of CF, later confirmed by elevated sweat chloride concentrations or positive DNA testing. We suggest that CBAVD patients with altered NPD should undergo further clinical follow-up in order to detect possible late complications of CF.

Mutation frequency of cystic fibrosis transmembrane regulator is not increased in oligozoospermic male candidates for intracytoplasmic sperm injection

OBJECTIVE

To examine the frequency of anomalies of the vas deferens and the frequency of mutations of the cystic fibrosis transmembrane regulator (CFTR) gene in male candidates for intracytoplasmic sperm injection (ICSI) who had severe oligoasthenoteratozoospermia.

DESIGN

The clinical data for male candidates for ICSI were studied. The three most frequent cystic fibrosis (CF)-causing CFTR mutations in the Dutch population (deltaF508, A455E, and G542X) and the three most frequent CFTR mutations potentially causing congenital bilateral absence of the vas deferens (CBAVD) in the Dutch population (deltaF508, R117H, and IVS8-5T) were analyzed. Delta I507 is also detected by the deltaF508 test. Samples of DNA from patients identified as CFTR mutation carriers were subjected to denaturing gradient gel electrophoresis analysis with use of a two-dimensional electrophoretic technique.

SETTING

University-based center for reproductive medicine and clinical genetics.

PATIENT(S)

Male candidates for ICSI who had oligoasthenoteratozoospermia and no history of operative sterilization and refertilization. Males with a chromosomal aberration or a Y-chromosome microdeletion were excluded.

INTERVENTION(S)

Semen and blood samples were collected from the patients at their first visit to the clinic.

MAIN OUTCOME MEASURE(S)

Frequency of anomalies of the vas deferens and frequency of mutations of the CFTR gene in male candidates for ICSI who had oligoasthenoteratozoospermia.

RESULT(S)

None of the patients had abnormalities of the vas deferens at physical examination. In 4 of the 150 chromosomes (75 patients), a CFTR mutation was found, yielding a CFTR mutation frequency of 2.7% (95% confidence interval, 1.0-6.7%). None of the patients had two CFTR mutations.

CONCLUSION(S)

The frequency of congenital abnormalities of the vas deferens in patients with oligoasthenoteratozoospermia is low. The frequencies of the CFTR mutations identified in this cohort did not differ significantly from the frequencies found in the normal Dutch population.

Sertoli cell expression of the cystic fibrosis transmembrane conductance regulator

Mutations of the cystic fibrosis transmembrane conductance regulator (CFTR) gene have been associated with a number of male reproductive problems, including testis abnormalities and a reduction in germ cell quality and number. To establish at least one site of functional CFTR expression in the testis, we subjected cultured Sertoli cells to analysis of message, protein, and channel activity for CFTR. With reverse transcription-polymerase chain reaction, we obtained evidence for the presence of CFTR RNA when CFTR primers were used with RNA from cultured Sertoli cells. Western analysis performed with both anti-R and anti-C domain CFTR antibodies revealed immunoreactive material in extracts from primary Sertoli cell cultures that seemed consistent with CFTR previously identified in other cells and tissues. This led us to perform more detailed studies using the whole cell arrangement of the patch-clamp technique. Application of the membrane-soluble cAMP analog, 8-chlorophenyl-thio-cAMP, resulted in the activation of a Cl- current that displayed a permeability sequence of Br- > I- > or = Cl- and was blocked by diphenylamine-2-carboxylate and glibenclamide. In addition, a 13-pS conductance Cl- channel was measured in excised membrane patches exposed to the catalytic subunit of protein kinase A. When taken together, our findings of evidence of CFTR message, immunoreactive material that appeared consistent with CFTR, and Cl- channels with properties similar to those reported for CFTR provide strong evidence that Sertoli cells express a functional CFTR-like protein. The presence of CFTR in these cells may be needed to maintain the specific nutritional and fluid balance in the seminiferous tubule that is vital for normal spermatogenesis.

The genetics of male infertility in relation to cystic fibrosis

Absence, dysfunction or low levels of cystic fibrosis (CF) transmembrane conductance regulator (CFTR) protein result in a broad range of clinical manifestations with CF with pancreatic insufficiency at the severe end of the phenotypic spectrum and, at the other end relatively mild clinical conditions, including several forms of male infertility. The condition of congenital bilateral absence of the vas deferens (CBAVD) is in 75-80% of the patients associated with defects in the CFTR gene. In the remaining patients, CBAVD is also associated with urinary tract malformations, and this form of CBAVD is not related to CF. Congenital unilateral absence of the vas deferens also seems to be associated with CF except when associated with renal abnormalities at the ipsilateral side of the absent vas. A possible role of the CFTR protein in the aetiology of infertility due to defects in sperm production and maturation has also been suggested recently. In contrast, Young's syndrome is probably not related to CF. The relation between some conditions of male infertility and CF implies appropriate clinical examination of the patients, CFTR mutation analysis and genetic counselling. Because infertility can now in many cases be treated by artificial reproductive technology couples have an increased risk of having children with CF or infertility if the female partner is also a carrier of a CFTR mutation. Couples should be well informed about these risks and risk prevention including pre-implantation diagnosis. Follow-up studies of children born to these couples are mandatory, whether male infertility is linked to CF or not.

Congenital absence of the vas deferens: incomplete penetrance of cystic fibrosis gene mutations

PURPOSE

We evaluated the penetrance of cystic fibrosis gene mutations for the clinical phenotype of congenital bilateral absence of the vas deferens.

MATERIALS AND METHODS

We retrospectively reviewed the fertility status of 244 brothers of 105 men with congenital bilateral absence of the vas deferens. Testing for the most common cystic fibrosis transmembrane conductance regulator (CFTR) gene mutations and for haplotype analysis of the intron 8/polythymidine segment was recommended for all men with congenital bilateral absence of the vas deferens.

RESULTS

Of 244 brothers of men with congenital bilateral absence of the vas deferens 131 were eligible for assessment of fertility. Of the 131 evaluable brothers only 7 (5%) were found to have congenital bilateral absence of the vas deferens. This prevalence is 5 times lower than that predicted for congenital bilateral absence of the vas deferens (25%) based on the autosomal recessive inheritance pattern seen in classical cystic fibrosis. For couples in which the man has congenital bilateral absence of the vas deferens and the female partner tests negative for standard CFTR gene mutations including 5T analysis, the maximum risk of having a child with congenital bilateral absence of the vas deferens is less than 1.0%.

CONCLUSIONS

Our data are consistent with incomplete penetrance for the congenital bilateral absence of the vas deferens phenotype after inheritance of cystic fibrosis gene mutations, even after adjusting for environmental factors and wolffian anomalies. Incomplete penetrance may account for a low prevalence of congenital bilateral absence of the vas deferens in the population and may lower the risk of having a child with congenital bilateral absence of the vas deferens for couples undergoing sperm retrieval and assisted reproductive techniques.

Disease-associated mutations in the fourth cytoplasmic loop of cystic fibrosis transmembrane conductance regulator compromise biosynthetic processing and chloride channel activity

A cluster of 18 point mutations in exon 17b of the cystic fibrosis transmembrane conductance regulator (CFTR) gene has been detected in patients with cystic fibrosis. These mutations cause single amino acid substitutions in the most C-terminal cytoplasmic loop (CL4, residues 1035-1102) of the CFTR chloride channel. Heterologous expression of the mutants showed that 12 produced only core-glycosylated CFTR, which was retained in the endoplasmic reticulum; the other six mutants matured and reached the cell surface. In some cases substitution of one member of pairs of adjacent residues resulted in misprocessing, whereas the other did not. Thus, the secondary structure of CL4 may contribute crucially to the proper folding of the entire CFTR molecule. Cyclic AMP-stimulated iodide efflux was not detected from cells expressing the misprocessed variants but was from the other six, indicating that their mutations cause relatively subtle channel defects. Consistent with this, these latter mutations generally are present in patients who are pancreatic-sufficient, while the processing mutants are mostly from patients who are pancreatic-insufficient. Single-channel patch-clamp analysis demonstrated that the processed mutants had the same ohmic conductance as wild-type CFTR, but a lower open probability, generally due to an increase in channel mean closed time and a reduction in mean open time. This suggests that mutations in CL4 do not affect pore properties of CFTR, but disrupt the mechanism of channel gating.

Mutations in the cystic fibrosis gene in patients with congenital absence of the vas deferens

BACKGROUND

Congenital bilateral absence of the vas deferens (CBAVD) is a form of male infertility in which mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene have been identified. The molecular basis of CBAVD is not completely understood. Although patients with cystic fibrosis have mutations in both copies of the CFTR gene, most patients with CBAVD have mutations in only one copy of the gene.

METHODS

To investigate CBAVD at the molecular level, we have characterized the mutations in the CFTR gene in 102 patients with this condition. None had clinical manifestations of cystic fibrosis. We also analyzed a DNA variant (the 5T allele) in a noncoding region of CFTR that causes reduced levels of the normal CFTR protein. Parents of patients with cystic fibrosis, patients with types of infertility other than CBAVD, and normal subjects were studied as controls.

RESULTS

Nineteen of the 102 patients with CBAVD had mutations in both copies of the CFTR gene, and none of them had the 5T allele. Fifty-four patients had a mutation in one copy of CFTR, and 34 of them (63 percent) had the 5T allele in the other CFTR gene. In 29 patients no CFTR mutations were found, but 7 of them (24 percent) had the 5T allele. In contrast, the frequency of this allele in the general population was about 5 percent.

CONCLUSIONS

Most patients with CBAVD have mutations in the CFTR gene. The combination of the 5T allele in one copy of the CFTR gene with a cystic fibrosis mutation in the other copy is the most common cause of CBAVD: The 5T allele mutation has a wide range of clinical presentations, occurring in patients with CBAVD or moderate forms of cystic fibrosis and in fertile men.