Though clinical studies with conflicting results have been published, PWS-associated obesity exhibits clinical characteristics that are somewhat different from those of essential obesity (EOB), including body composition (particularly, adipose tissue), neuroendocrine system (e.g., ghrelin, oxytocin, and adiponectin), response to body weight reduction programs, occurrence of obesity-related comorbidities such as type 2 diabetes mellitus (T2DM), and long-term cardiovascular prognosis (6–12). The gene discussed is OXT; the disease is type 2 diabetes mellitus.