CONGENITAL BILATERAL ABSENCE OF THE VAS DEFERENS (CBAVD)

SCIENTIFIC BACKGROUND

Congenital bilateral aplasia of the vas deferens (CBAVD) causes male infertility and may occur in isolation or as a manifestation of cystic fibrosis (CF). Obstruction of the vas deferens, due to degenerative changes, is responsible for infertility. CBAVD is understood to be an atypical, monosymptomatic form of CF and is grouped under CFTR-associated disorders (CFTR-RD). Here, pathogenic alterations in the CFTR gene lead to dysfunction of a chloride channel in the apical cell membrane of glandular epithelial cells and ultimately to alteration of the salt content of sweat and other body secretions.

The heterozygote frequency for pathogenic CFTR variants is estimated to be 1:25 in the Caucasian population. However, the spectrum of pathogenic variants differs from that of CF. In 40-50% of Caucasian CBAVD patients, at least one of the following three pathogenic alterations in the CFTR gene is detectable: p.(Phe508del), p.(Arg117His), 5T allele. Typically, CBAVD is a combination of one "severe" (e.g., p.(Phe508del)) and one "mild" CFTR variant (e.g., p.(Arg117His)) or two "mild" CFTR variants. Even if only one pathogenic alteration is detectable, it is still assumed that there's a second alteration not detectable with current testing methods. It is recommended to examine the partner of a CFTR carrier for pathogenic changes in the CFTR gene before a planned artificial insemination (ICSI). If a pathogenic CFTR variant is detected in both partners, the joint offspring has a 25% risk of having CF, and therefore, genetic counseling is recommended.

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