It is also important to note that, of the possible enzyme deficiencies that result in CAH, only the 21-hydroxylase gene in CYP21A2 and pseudogene CYP21P are located in the class III region of the major histocompatibility complex; the 11b-hydroxylase gene is located in chromosome 8q, and the 17-hydroxylase gene is located in chromosome 10 [12]. The gene discussed is CYP21A2; the disease is congenital adrenal hyperplasia.