DR2-positive monozygotic twins discordant for narcolepsy.

Narcolepsy runs in families, and recent research has revealed the human leukocyte antigen (HLA) DR2 to be a genetic marker closely associated with the disease. But, as indicated by family studies, other factors contribute to the pathogenesis of narcolepsy. The investigation of monozygotic twins is the most specific research tool for distinguishing between a multigenetic and a multifactorial pathogenetic model. We present clinical and sleep polygraphic data from two pairs of monozygotic twins, and in addition, from some of their first-degree relatives. In both pairs only one twin suffered from the clinical symptoms of narcolepsy/cataplexy. Only in these subjects did night sleep recordings and a multiple sleep latency test reveal both multiple sleep onset rapid-eye-movement periods (SOREMPs) and short mean sleep onset latencies. However, in two of the asymptomatic, HLA DR2+ relatives, short mean sleep onset latencies during the multiple sleep latency test (MSLT) were observed, and one, HLA DR2- relative showed REM sleep two times during the MSLT. Our results strongly favor a multifactorial pathogenetic model for narcolepsy.