Obstructed Vas Deferens
The most common reason for an absence of sperm in the semen is obstruction in the flow of sperm through the vas deferens on either side. This condition, called congenital bilateral absence of the vas deferens (CBAVD), is a primarily genital form of cystic fibrosis (CF).
Men with this disorder have invariably inherited two different, often uncommon or rarer CF gene mutations from either parent. These men manufacture normal sperm but have undeveloped vas and cannot deliver sperm. They are not sterile, since sperm can be obtained through needle aspiration from the testis, followed by in vitro fertilization (fertilization of the partner's harvested egg in a dish, followed by placement of the fertilized egg in the partner's womb). Incidentally, men with CF who have lung and/or pancreatic involvement are almost always azoospermic because of this problem with the vas deferens.
Men with CBAVD or CF should have a CF gene DNA mutation analysis before trying to have children. Their partners should also be tested; one in 25 caucasians are carriers of a CF gene mutation. At Boston University Center for Human Genetics, we assay for 100 CF mutations, providing the highest mutation detection rates available by clinical testing.