Obesity is the most obvious physical feature of Prader-Willi syndrome (PWS). About one-third of individuals with untreated PWS weigh more than 200% of their ideal body weight. The paradox of the underweight infant with PWS evolving into an overweight or obese child and adult has led to considerable speculation regarding pathophysiology [Mutch: 2006] [Miller: 2006] [Holsen: 2006]

Four recognized factors contributing to obesity in PWS are:

• Hyperphagia or overeating beginning in early childhood (between 1-6 years)
• Reduced physical activity relating to decreased muscle tone and quantity, and increased fat mass
• Reduced metabolic rate (about 60% of normal) related to decreased muscle mass
• Inability to vomit

Obesity-related findings include:

• Heart failure
• Hypertension
• Thrombophlebitis and chronic leg edema
• Ulcers and cellulitis
• Orthopedic problems
• Abnormal lipid profiles
• Diabetes mellitus, type II

Other findings seen at an increased rate when compared to the general population with obesity include:

• Obstructive sleep apnea
• Narrowing of the airway
• Impaired respiratory function
• Hypoventilation
• High carbon dioxide levels
• Increased risks of complications with general anesthesia
• Hypometabolism

Effective strategies to prevent or limit obesity are necessary throughout the lifespan of individuals with PWS:

• Weight control through diet restriction (about 60% of normal daily caloric intake)
• Exercise programs tailored to the individual’s health status, age, and jointly established goals
• Sex hormone therapy and growth hormone therapy, which leads to increased height, decreased fat mass, increased muscle mass, and increased metabolic rate