CFTR and Blindness: Mutations in the CFTR Cl− channel cause male infertility by a developmental defect, resulting in congenital absence of vas deferens (49), but Cftr−/− mice are fertile (50), whereas loss-of-function mutations in ClC-2 result in another form of syndromal male infertility that prominently includes leukodystrophy and blindness as additional pathologies (33, 51, 52).