Molecular and Functional Characterization of CBAVD-Causing Mutations Located in CFTR Nucleotide-Binding Domains

Abstract

Background: About 98% of male affected with cystic fibrosis (CF [MIM 219700]) are infertile due to bilateral absence of vas deferens (CBAVD [MIM 277180]), which makes up 1-2 % of all cases with male infertility. A previous screening of the entire coding region of the cystic fibrosis transmembrane conductance regulator gene (CFTR [MIM 602421]) in CBAVD patients identified three novel mutations: P439S is located in the first nucleotide binding domain (NBD1) of CFTR, whereas P1290S and E1401K are located in NBD2. Methods: We analysed the effects of these novel mutations on CFTR processing and chloride (Cl^-) channel activity. Results: Although maturation patterns were not affected, total amounts of mature P439S-CFTR and P1290S-CFTR were reduced. Confocal microscopy showed correct membrane localisation of E1401K-CFTR, whereas P439S-CFTR and P1290S-CFTR mutants were located mainly in the cytoplasm. Iodide influx assay and whole-cell patch clamp demonstrated significantly reduced cAMP-dependent anion conductances for all three mutants. Conclusion: Dysfunction of CFTR is caused by either defective CFTR trafficking (P439S and P1290S) or/and Cl- channel function (P1290S and E1401K). Thus reduced Cl- conductance caused by the three CFTR mutations affects normal development of vas deferens and leads to CBAVD, but the remaining function is sufficient to prevent other typical CF symptoms.

The H-loop in the Second Nucleotide-binding Domain of the Cystic Fibrosis Transmembrane Conductance Regulator is Required for Efficient Chloride Channel Closing

“…7D). Similar decrease in whole-cell currents has been very recently reported for another H-loop mutation E1401K, associated with CBAVD [66]. The above results may seem surprising in light of our finding that the HR→AA CFTR mutant shows increased open probability in single-channel analysis (Fig.…”

Meta-analyses of 4 CFTR variants associated with the risk of the congenital bilateral absence of the vas deferens

“…CBAVD is responsible for 1-2% of male infertility [1]. CBAVD was widely considered as an atypical symptom of cystic fibrosis (CF, MIM: #219700) [2,3], which was a severe recessive disease characterized by obstructive chronic lung disease, pancreatic disease and abnormal concentrations of electrolytes in the sweat in clinical studies [4].…”

“…CBAVD incidence is rare (1-2%) in the patients with male infertility [1]. Most genetic studies only involved a few number of individuals.…”

Management of male infertility due to congenital bilateral absence of vas deferens should not ignore the diagnosis of cystic fibrosis

“…In contrast, classes IV and V mutations cause a mild CF phenotype because of a residual CFTR protein activity. The type of CFTR mutation appears to be fundamental to modulate clinical expression of the disease (Grangeia et al ., ; Dequeker et al ., ). Indeed, CFTR genotype of CBAVD includes generally at least one mild mutation: one mild and one severe mutation in 88% of patients with CBAVD or two mild mutations in 12% of them (Gervais et al ., ; Radpour et al ., ,b; Ratbi et al ., ).…”