Taro Adachi,
Prader-Willi Syndrome (PWS) is a genetic disorder with several clinical features, such as excessive daytime sleepiness (EDS). However, it is difficult to delineate which sleep disorder causes EDS in patients with PWS because they have several risks of EDS, including obstructive sleep apnea (OSA), narcolepsy, and manifestation of PWS. We present the case of an obese 11-year-old boy with PWS who experienced EDS and excessive weight gain concurrently. He was diagnosed with PWS at the age of 5 months. At the age of 10 years, he gradually gained weight and developed symptoms of EDS. His attending family doctor referred him to our clinic to assess OSA using nocturnal polysomnography; however, there were no signs of sleep apnea. Results of the multiple sleep latency test did not fulfil the diagnostic criteria for narcolepsy. We concluded that the EDS in this patient was due to a direct symptom of PWS.
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