The etiology of obesity in youth with DS is unclear (20), but Bertapelli et al. (18) suggest the increased rates of obesity are associated with both physiological factors, such as increased leptin, decreased resting energy expenditure (REE), hypotonia, DS associated comorbidities, and lifestyle factors such as an unhealthy diet, and low physical activity levels. The gene discussed is LEP; the disease is obesity due to melanocortin 4 receptor deficiency.