95% of white patients with narcolepsy have the HLA DR2 (HLA DR 15 in the new terminology) genotype.
100% of black patients with narcolepsy have the HLA DQ w1 (HLA DQ w6 in the new terminology) genotype.
The environment may be important because there is only a 25% concordance for narcolepsy in monozygotic twins.
The risk of narcolepsy in first degree relatives of sufferer is 1-2% (a relative risk of 40).
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