Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Congenital bilateral absence of the vas deferens ?
    ### Response:
    Congenital bilateral absence of the vas deferens (CBAVD) occurs in males when the tubes that carry sperm out of the testes (vas deferens) fail to develop properly. Although the testes usually develop and function normally, sperm cannot be transported through the vas deferens to become part of semen.
    