Defects in any of the enzymatic reactions in the pathway from cholesterol to testosterone can impair virilisation of the male embryo (see Fig. 11.7). Defects in P450scc, P450l7a, and 3b-HSD enzymes also result in congenital adrenal hyperplasia. In all of the enzymatic defects, Mullerian regression is usually normal. The masculinisation of the Wolffian ducts, urogenital sinus, and urogenital tubercle and virilisation at puberty vary from almost normal to absent and, therefore, the phenotype varies from men with mild hypospadias to women. This variability is due to the varying severity of the enzymatic defects and the varying effects of the steroids that accumulate proximal to the metabolic blocks. In subjects with partial defects, diagnosis may require measurement of the steroids that accumulate proxima, to the metabolic block.
