FGD has been identified with mutations in the melanocortin-2 receptor gene (MC2R) (~ 25% of patients), the MRAP gene encoding the MC2R accessory protein (~ 20% of patients), the steroidogenic acute regulatory gene (STAR; ~ 5% of patients), and by a single mutation in the mini-chromosome maintenance-deficient 4 homolog gene (MCM4) in the Irish Traveler population [reviewed in ref [15]]. This evidence concerns the gene STAR and Aarskog-Scott syndrome, X-linked.