FGD4 and Aarskog-Scott syndrome, X-linked: FGD exhibits genetic heterogeneity, with five main subtypes classified according to their associated genes: FGD1 [melanocortin-2 receptor associated protein (MC2R)], FGD2 [melanocortin receptor accessory protein 2 (MRAP)], FGD3 [steroidogenic acute regulatory protein (STAR)], FGD4 [nicotinamide nucleotide transhydrogenase (NNT)], and FGD5 (TXNRD2) (4).