A young couple has been unsuccessful in conceiving a child over a 4-month period. The 28-year-old wife had been extensively investigated by a female reproductive specialist, and no abnormalities were detected. The husband, who initially refused to undergo semen analysis now agreed to this investigation, which revealed a low volume and azotemia. Follicle-stimulating hormone (FSH) level is normal. What is the most likely diagnosis?

In congenital absence of the vas deferens, mutation of the cystic fibrosis transmembrane receptor gene (CFTg) occurs. The epididymis vas deferens, seminal vesicle, membranous urethra, part of the trigone of the bladder, and ureter arise from the mesonephric duct. In the presence of a normal FSH level, testicular biopsy would most likely confirm normal sperm formation. In the presence of a Sertoli cell tumor, spermatozoa are unlikely to form, and the FSH level is elevated.