Congenital bilateral absence of the vas deferens (ductus deferens) is a defect caused by a genetic mutation leading to male infertility. Congenital bilateral absence of the vas deferens in men occurs when the ducts that carry sperm from the testicles fail to develop properly. Although the testes normally develop and function normally, sperm cannot be transported through the vas deferens to enter the seminal fluid. As a result, men with this disorder suffer from infertility unless the use of assisted reproductive technologies is resorted to. It is not reported whether this condition affects sexual desire or sexual activity in men. Congenital bilateral absence of the vas deferens (CBAVD) can occur alone or as a sign of cystic fibrosis (cystic fibrosis), an inherited disease in which the body produces an abnormally thick viscous secretion. Cystic fibrosis causes progressive damage to the respiratory system and chronic problems with the digestive system. A large proportion of men with congenital bilateral vas deferens do not have the other signs of cystic fibrosis. However, some men with this condition may experience mild respiratory or digestive problems. Congenital bilateral absence of the vas deferens is caused by mutations in the CFTR gene. More than half of all men with this defect have mutations in the CFTR gene. Mutations in this gene also cause cystic fibrosis. When congenital bilateral vas deferens with CFTR mutations occurs, without other features of cystic fibrosis, the condition is considered a form of atypical cystic fibrosis. The protein, whose production information is encoded by the CFTR gene, forms a channel that transports negatively charged particles called chloride ions in and out of cells. The flow of chloride ions helps control the movement of water into tissues, which is necessary for the production of thin, free-flowing mucus (secretion). Mucus serves to lubricate and protect the lining of the respiratory tract, digestive system, reproductive system, and other organs and tissues. Mutations in the CFTR gene disrupt the function of chloride channels, preventing them from regulating the flow of chloride ions and water across cell membranes. As a result, cells in the male genital tract produce mucus that is unusually thick and sticky. This mucus blocks the vas deferens while it is forming, causing the abnormality before birth. In cases of congenital bilateral absence of the vas deferens without a mutation in the CFTR gene, the cause of the condition is often unknown. Some cases of the abnormality are associated with other structural problems of the urinary tract. When this condition is caused by mutations in the CFTR gene, it is inherited in an autosomal recessive pattern. In this pattern of inheritance, both copies of the gene (received from both parents) in each cell must have the mutation,for the offense to be developed. Men with this disease who choose to become fathers through assisted reproduction have an increased risk of having a child with cystic fibrosis. If congenital bilateral vas deferens is not caused by mutations in the CFTR gene, the risk of having children with cystic fibrosis does not increase. References: 1. Cuppens H, Cassiman JJ. CFTR mutations and polymorphisms in male infertility 2. Daudin M, Bieth E, Bujan L, Massat G, Pontonnier F, Mieusset R. Congenital bilateral absence of the vas deferens: clinical characteristics, biological parameters, cystic fibrosis transmembrane conductance regulator gene mutations, and implications for genetic counseling 3. de Souza DAS, Faucz FR, Pereira-Ferrari L, Sotomaior VS, Raskin S. Congenital bilateral absence of the vas deferens as an atypical form of cystic fibrosis: reproductive implications and genetic counseling 4. Jarzabek K, Zbucka M, Pepinski W, Szamatowicz J, Domitrz J, Janica J, Wolczynski S, Szamatowicz M. Cystic fibrosis as a cause of infertility 5. Nick JA, Rodman DM. Manifestations of cystic fibrosis diagnosed in adulthood