ABSTRACT
A genetic component for narcolepsy has been consistently reported across all cultures. Since its initial description by Westphal in 1877, familial narcolepsy has been described by several authors (1,2), suggesting the existence of predisposing genetic factors. Nevsimalova-Bruhova and Roth reported in 1972 that 39.1% of 23 cases of idiopathic hypersomnia and 32.9% of 85 cases of narcolepsy had a positive family history of hypersomnia or narcolepsy (3), and suggested a polyfactorial type of inheritance with two or more genes to explain the transmission of narcolepsy. Kessler in 1976 (4) analyzed 130 narcoleptic families with a narcolepsy proband, and calculated the heritability of narcolepsy to be 0.74. Baraitzer and Parkes (5) analyzed 50 families with a narcolepsy proband and reported that 52% had affected first-degree relatives. Finally, Honda analyzed the mode of inheritance in 232 families with a narcolepsy proband and in 76 families with an excessive daytime sleepiness (EDS) proband (6), and calculated that the heritability of narcolepsy was 0.33 and the heritability of both narcolepsy and EDS was 0.62. There were no narcolepsy patients in families with an EDS proband. Honda proposed a two-threshold multifactorial inheritance model with dominant human leucocyte antigen (HLA)-Dw2 inheritance.
