A Novel Maternally Inherited GNAS Variant in a Family With Hyperphagia and Obesity: 3 Cases

GNAS variants were recently described in 1% of patients not known to have pseudohypoparathyroidism/inactivating PTH/PTHrP signalling disorder 2 in the UK Genetics of Obesity Study. We describe a new missense GNAS variant, c.791A > C, p.(Asp264Thr), in a family with obesity, hyperphagia and mild PTH resistance. A 6-year-old female (body mass index +4.3 SD score [SDS], height +1.9 SDS) presented with hyperphagia and obesity from age 3 years. She had subtle brachydactyly, macrocephaly, and mildly delayed development. The 12-year-old brother (height +2.1 SDS, body mass index +2.9 SDS) had hyperphagia, obesity, mildly delayed development, and autism. He had subtle brachydactyly, as did the affected mother. We assessed the functional effect of the mutant, measuring cAMP production in cells transfected with wild type and mutant GNAS after ligand stimulation. Cells with the mutant GNAS showed impaired cAMP generation through melanocortin receptor 4, GH releasing hormone receptor, and PTH receptor. These cases demonstrate the clinical heterogeneity of monogenic disease, suggesting a need to test for PHP1A in children with obesity even without classical signs of PHP1A.