The importance of STK39 in mouse spermatogenesis was demonstrated by Liu et al. [71], where a Sertoli cell-specific OSR1−/− and STK39−/− double-knockout male mice displayed infertility with increased germ cell apoptosis and defective spermatogenesis, resulting in Sertoli cell-only syndrome. The gene discussed is STK39; the disease is Sertoli Cell-Only Syndrome.