XY KO mice had a female appearance (external genital phenotype) (Fig. 1c); however, genotyping revealed a Mendelian ratio of XX and XY chromosomes (1:1), resembling the human phenotype in the rare form of the DSD and CAH, caused by CYP17A1 deficiency30. Here, CYP17A1 is linked to congenital adrenal hyperplasia.