In FGD, the two most common gene defects are mutations in the melanocortin 2 receptor and its accessory protein (MC2R and MRAP), but recently, we have described defects in NADPH supply to and/or antioxidant defence in mitochondria, with defects in two genes, NNT and thioredoxin reductase 2 (TXNRD2), giving disorders of adrenal insufficiency primarily compromising glucocorticoid production (Meimaridou et al. 2012, 2013, Prasad et al. 2014). Here, MC2R is linked to Adrenal insufficiency.