Prader-Willi syndrome (PWS) is a rare genetic disorder that affects about 1 in 14,000 people in the United States. As the most commonly identified genetic cause of obesity, PWS is often confused with Early-onset Morbid Obesity (EMO). Individuals with EMO show some signs of PWS, but clinically do not have PWS. The purpose of this study is to evaluate the clinical features and genetic basis of PWS and EMO, and to determine how these conditions affect a person throughout a lifetime.

PWS is a complex neurobehavioral syndrome. Clinical features include obesity, increased appetite, low muscle tone, cognitive impairment, distinct behavioral features, hypogonadism, and neonatal failure-to-thrive. It is the most commonly recognized genetic cause of obesity; however, many obese children do not in fact have PWS. These individuals are therefore diagnosed with EMO, a condition that shares features with PWS. The development of new advances and strategies for treating PWS and EMO requires a thorough understanding of the conditions at both the clinical and molecular levels. One goal of this study is to collect long-term data on individuals with PWS and EMO in order to gain a better understanding of the natural progression of the conditions, from the neonatal period well into adulthood. Specific to PWS, this study will establish a genotype-phenotype correlation among the different sub-types and will evaluate the effects of growth hormone treatment on disease progression. Lastly, the study will compare PWS with EMO in terms of clinical features and genetic basis.

Participation in this natural history study will entail an initial evaluation, followed by yearly study visits until the age of 3 and then every 2 years thereafter. Each study visit will last between 3 and 4 hours, and will include a physical exam (including a DEXA scan to determine body composition), psychological testing, an interview with the study physician, and an evaluation of the participant's diet history. In addition, blood tests will be completed for genetic testing and photos will be taken to evaluate disease progression. Cognitive and behavioral assessments will also be conducted and will last between 10 and 30 minutes.

• Prader-Willi Syndrome
• Obesity

• Individuals with Prader-Willi syndrome
• Individuals with Early-onset Morbid Obesity

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Inclusion Criteria:

• Individuals enrolling in the Prader-Willi syndrome group will have a confirmed diagnosis of Prader-Willi syndrome, as confirmed by molecular and cytogenetic testing
• Individuals enrolling in the Early-onset Morbid Obesity group will have a documented medical history of their weight exceeding 150% of the ideal body weight or a body mass index greater than 97% before the age of 4 years; they will also be under the age of 30 years.

Exclusion Criteria:

• Known genetic, chromosomal, or hormonal cause of cognitive impairment other than Prader-Willi syndrome