Screening for hormonal, monogenic, and syndromic disorders in obese infants and children.

The prevalence of pediatric obesity in the United States is nearly 17%. Most cases are "exogenous", resulting from excess energy intake relative to energy expenditure over a prolonged period of time. However, some cases of obesity are "endogenous", associated with hormonal, genetic, or syndromic disorders such as hypothyroidism, Cushing's syndrome, growth hormone deficiency, defective leptin signaling, mutations in the melanocortin 4 receptor, and Prader-Willi and Bardet-Biedl syndromes. This article reviews the hormonal, monogenic, and syndromic causes of childhood obesity and identifies critical features that distinguish "endogenous" obesity disorders from the more common exogenous obesity. Findings that raise suspicion for endogenous obesity include onset in infancy, lack of satiety, poor linear growth, dysmorphic features, and cognitive dysfunction. Selection and interpretation of appropriate laboratory tests and indications for subspecialist referral are also discussed.