Cystic fibrosis and infertility caused by congenital bilateral absence of the vas deferens and related clinical entities.

The condition of congenital bilateral absence of the vas deferens (CBAVD) is, in the majority of patients, related to defects in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. CBAVD patients either are compound heterozygotes (carrying different mutations in their two CFTR genes) or carry a mutation in one of their CFTR genes and an intron 8 5T splice variant, associated with low levels of functional CFTR protein, in their second gene. The relationship between cystic fibrosis (CF) and CBAVD requires a proper clinical examination of the patient, a CFTR mutation analysis for himself and his family and genetic counselling. A mutation analysis should also be performed for the wives of CBAVD males because such couples now have the possibility of having their own genetic children but are at increased risk of having children with CF and/or CBAVD. The aetiology of some conditions of CBAVD is not related to CF, especially when CBAVD is associated with urinary tract malformations (up to 20% of cases). In couples with CBAVD not related to CF there is no increased risk of CF children, but it is not known whether they have an increased risk of having sons with CBAVD. In some of the patients with congenital unilateral absence of the vas deferens (CUAVD) the condition is also related to CF, especially in cases where there is an occlusion of the palpable vas. The CFTR gene is probably not involved in the aetiology of Young's syndrome. Follow-up studies of children born to couples where the males have CBAVD, CUAVD or Young's syndrome are mandatory and will help to better define the risk to their offspring of CF and/or of inheriting their paternal infertility condition.