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.