Steroid 17-alpha-hydroxylase/17,20 lyase (CYP17A1) mediates both 17-alpha-hydroxylase and 17,20-lyase activity, allowing the adrenal glands and gonads to synthesise both 17-alpha-hydroxylated glucocorticoids and sex steroids respectively (Kagimoto et al. 1998). Defects in CYP17A1 can cause Adrenal hyperplasia 5 (AH5), a form of congenital adrenal hyperplasia (CAH), a common recessive disease due to defective synthesis of cortisol and sex steroids. Common symptoms include mild hypocortisolism, ambiguous genitalia in genetic males or failure of the ovaries to function at puberty in genetic females, metabolic alkalosis due to hypokalemia and low-renin hypertension. CYP17A1 can have defects in either or both of 17-alpha-hydroxylase and 17,20-lyase activities thus patients can show combined partial 17-alpha-hydroxylase/17,20-lyase deficiency or isolated 17,20-lyase deficiency traits (Yanase et al. 1992, Kater & Biglieri 1994, Fluck & Miller 2006, Miller 2012).