Congenital bilateral absence of the vas deferens (CBAVD) accounts for 1%-2% of sterility in men. A high incidence of mutations, as well as the involvement of the 5T variant of the T tract length in intron 8 of the cystic fibrosis conductance regulator (CFTR) gene, have been previously described in males with CBAVD. Herein we report the screening for mutations and for the 5T variant of the CFTR gene in 17 patients with CBAVD and three others with non-CABVD obstructive azoospermia. In the CBAVD

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... oup, three patients (15%) were compound heterozygotes for mutations, and five patients (25%) had a mutation in one allele and the 5T variant in the other; the 5T variant was also present in two other patients, one of them being homozygous. The most frequent mutation was ∆F508, present on five chromosomes (12.5%). A novel missense mutation (A399D) was detected in a Japanese CBVAD patient. Our results yield further evidence for a strong association between male obstructive azoospermia caused by CBAVD and mutation/5T variant in the CFTR gene. The search for CFTR mutations in such patients is thus recommended for genetic counseling of couples who undergo assisted fertilization due to CBAVD.