Snapshot A 2-year-old boy is brought to the pediatrician as a new patient. His mother reports that since he was young, he has fed very poorly, and has had decreased muscle tone compared to his siblings. Recently, he started displaying behavioral issues, such as hyperphagia. On physical exam, he is short, overweight, and has cryptorchidism. The pediatrician sends him for screening test for growth hormone deficiency, as well as to a geneticist for possible genetic testing. Introduction Overview Prader-Willi syndrome is a disorder of imprinting associated with mutation or deletion of chromosome 15q11-13 login to view 1 more bullet Epidemiology incidence login to view 1 more bullet Pathogenesis the maternal allele on chromosome 15q11.2-13 is normally methylated or silenced mutation or deletion of the paternal allele then results in complete absence or defective gene expression, leading to Prader-Willi syndrome Genetics inheritance pattern login to view 1 more bullet mutations login to view 3 more bullets Associated conditions growth hormone deficiency Prognosis patients are typically able to function well into adulthood Presentation Symptoms intellectual disability hyperphagia behavioral problems Physical exam neonate and infant login to view 6 more bullets toddlers login to view 1 more bullet children login to view 5 more bullets Imaging Radiograph indication login to view 1 more bullet findings login to view 1 more bullet Studies Serum labs fasting levels of insulin-like growth factor 1 and insulin-like growth factor binding protein-3 login to view 2 more bullets Genetic testing chromosomal or microarray analysis prenatal testing via chorionic villus sampling or amniocentesis Differential Angelman syndrome key distinguishing factors login to view 2 more bullets Treatment Lifestyle behavioral therapy login to view 1 more bullet diet and exercise login to view 1 more bullet calorie restriction Medical growth hormone login to view 3 more bullets hormone-replacement therapy login to view 2 more bullets Surgical feeding tube login to view 2 more bullets Complications Hypopituitarism with deficiency in growth hormone Scoliosis Obstructive sleep apnea Cor pulmonale