CFTR and cystic fibrosis: Screening for CFTR mutations in infertile men is carried out after identification of congenital absence of the vas deferens, since mutations in the CFTR gene can cause both a severe hereditary disease of cystic fibrosis and aplasia of the vas deferens (Havasi et al., 2010; Ahmad et al., 2013; Jiang et al., 2017).