Patients with maternally inherited GNAS mutations develop pseudohypoparathyroidism type 1A (PHP1A) and exhibit extraskeletal manifestations that include obesity and resistance to multiple hormones requiring Gαs, such as PTH, TSH, GHRH, and LH/FSH, [18–24] whereas patients with paternally derived GNAS mutations develop pseudopseudohypoparathyroidism (PPHP), in which patients have AHO skeletal features without severe obesity [25] or hormonal resistance (for review [6–11]). Here, GNAS is linked to obesity due to melanocortin 4 receptor deficiency.