HSD17B3 and hyperinsulinemic hypoglycemia, familial, 4: The importance of the combined hCG-testosterone system as a crucial combined switch for sex differentiation is underlined by DSD individuals with inactivating molecular variations in several of the involved genes, e. g., in Leydig cell hypoplasia [47], StAR deficiency [48], P450scc deficiency [49], 3ß-hydroxysteroid dehydrogenase type II deficiency [50], 17alpha/17,20 lyase deficiency [51], 17ß hydroxysteroid dehydrogenase type III deficiency [52] and 5alpha-reductase type 2 deficiency due to mutations in the SRD5A2 gene [53, 54].