Idiopathic hypersomnia: a report of three adolescent-onset cases in a two-generation family.

Idiopathic hypersomnia is an uncommon sleep disorder characterized by prolonged sleep time and excessive daytime sleepiness without cataplexy. This study concerned a case of familial occurrence. The proband expressed an idiopathic hypersomnia with long sleep time at the age of 12 years. Clinical interview and ad libitum polysomnographic study did not reveal any symptoms of narcolepsy or other sleep disorders. Family history revealed that a 20-year-old sister had experienced symptoms of hypersomnia from the age of 16 and their mother had been diagnosed with idiopathic hypersomnia previously. The diagnosis of idiopathic hypersomnia with long sleep time was confirmed in the sister by clinical interview and ad libitum polysomnography. Human leukocyte antigen (HLA) did not reveal the DQB1-0602 phenotype in the proband and relatives. This report confirms the hypothesis of a genetic predisposition in idiopathic hypersomnia.