We describe a novel heterozygous inactivating GNAS variant c.791A > C, p.(N264T) resulting in hyperphagia, obesity, developmental delay, mild brachydactyly, a variable effect on height and head circumference, and biochemical mild PTH resistance, fulfilling criteria for a diagnosis of AHO and PHP1A/IPPSD2 in 2 siblings and a similar phenotype without cognitive impairment and normal height in their mother, the phenotype cosegregating in the pedigree. Here, GNAS is linked to obesity due to melanocortin 4 receptor deficiency.