[A six year-old case of narcolepsy].

We report here a 6-year-old boy with narcolepsy. The diagnostic criteria were met by the clinical symptoms including excessive daytime sleepiness and cataplexy, and by the results of overnight polysomnography (PSG), multiple sleep latency test (MSLT), and human leukocyte antigen (HLA). PSG showed increased ratio of sleep stages 1 and 2 due to frequent awakening. All the five test session of MSLT showed a sleep onset REM period. HLA typing was positive for DRB1* 1501 and DQB1* 0602. Though the present case had very early onset, all the clinical symptoms and results of sleep studies met the criteria of narcolepsy. The CSF orexin level was far below the lower limit of the control values. It is very useful to measure CSF orexin for the diagnosis of early onset narcolepsy.