Below is an instruction from Human. Write a response.
    ### Instruction:
    What are the genetic changes related to congenital bilateral absence of the vas deferens ?
    ### Response:
    Mutations in the CFTR gene cause congenital bilateral absence of the vas deferens.  More than half of all men with this condition have mutations in the CFTR gene. Mutations in this gene also cause cystic fibrosis. When congenital bilateral absence of the vas deferens occurs with CFTR mutations, it is considered a form of atypical cystic fibrosis.
    