SPINK2 and Azoospermia: Homozygous SPINK2 mutation leads to azoospermia in men [86]. Decreased SPINK2 expression in azoospermic infertile men [87]. Spink2 mutant mice have elevated serine protease activity and exhibit impaired fertility [88]. Spink2−/− mice are azoospermic and infertile [86]