Cytochrome P450 11B1, mitochondrial (CYP11B1) possesses steroid 11-beta-hydroxylase activity which can convert 11-deoxycortisol to cortisol. 11-beta-hydroxylase deficiency is one of the main causes of congenital adrenal hyperplasia (CAH) (5-8%), second only to 21-hydroxylase deficiency which accounts for more than 90% of CAH (Zhao et al. 2008). Defects in CYP11B1 can cause Adrenal hyperplasia 4 (AH4; MIM:202010), a form of congenital adrenal hyperplasia which is a common recessive disease due to failure to convert 11-deoxycortisol to cortisol. This impaired corticosteroid biosynthesis results in androgen excess, virilization and hypertension (White et al. 1991).