A rare genetic condition present at birth. Neonates present with hypotonia, developmental delay, difficulty feeding, weak suck, weak cry, dolichocephaly, genital hypoplasia, and failure to thrive. As patients develop, physical features include a narrow face, almond-shaped eyes, triangular mouth with small upper lip, light skin, and light hair as well as short stature and small hands and feet. Starting in childhood, hyperphagia results in weight gain, often leading to morbid obesity. Patients may have cognitive impairment, delayed puberty, sleep abnormalities, and behavior issues (eg, stubbornness, short temper, and obsessive-compulsive disorder-like behaviors such as skin picking). Complications of obesity include type 2 diabetes, hypertension, and sleep apnea. Many patients do not live past the fifth decade due to complications from obesity.

Caused by a gene mutation on the long arm of chromosome 15. Most cases are the result of new mutations, but the condition can be the result of autosomal dominant inheritance.