Diagnostic criteria for narcolepsy and HLA-DR2 frequencies

HLA-DR2 frequencies were investigated in Japanese patients with narcolepsy as defined by various diagnostic criteria. The DR2 frequency was 100% when our criteria for narcolepsy were employed. The use of other criteria that lacked cataplexy as an obligatory symptom, however, reduced the DR2 frequency and led to an apparent "discovery" of DR2-negative cases with "narcolepsy". This observation indicates the necessity of precise diagnostic criteria in research on the HLA-narcolepsy association.