Objective: Five Japanese studies, to the authors' knowledge, without exception, have consistently shown an increased frequency of human leukocyte antigen (HLA)-DR1 in patients with schizophrenia. This suggests an association between HLA-DR1 and schizophrenia in the Japanese population. The mechanism of the association is unknown; however, prenatal infections may be involved. The present study explored factors, including winter birth, that might correlate with this mechanism. Age at onset and gender were also studied.
Method: Factors were compared between Japanese patients with schizophrenia with and in those without HLA-DR1 (N=60 and N=307, respectively).
Results: A significantly higher incidence of births in February and March was observed in patients with (31.7%) than those without (15. 6%) HLA-DR1. No association was found between the presence of HLA-DR1 and other variables.
Conclusions: Although this result is preliminary, it may suggest an interaction between HLA and winter birth in the development of schizophrenia in the Japanese population.