CFTR and Azoospermia: CFTR mutants also occur in non-CBAVD obstructive azoospermia and spermatogenetic failure, where the frequency of CFTR mutants, such as the 5T allele, is lower than that in CBAVD (Stuppia et al., 2005; Asadi et al., 2019; Rudnik-Schöneborn et al., 2021).