Summer birth and deficit schizophrenia in Dumfries and Galloway, southwestern Scotland.

OBJECTIVE: An association between deficit schizophrenia and summer birth has previously been reported. Confirmation of a separate risk factor for this group of patients is potentially important, but the number of subjects with deficit schizophrenia in previous reports has been small. This analysis used data from an epidemiological study of incident cases of psychosis to test the hypothesis that deficit schizophrenia is associated with summer birth.
METHOD: Data were drawn from records for the first year of clinical contact for all new patients coming into treatment for psychosis in the region of Dumfries and Galloway, Scotland, from 1979 to 1998. Patients with schizophrenia were classified as having deficit (N=65) or nondeficit (N=277) schizophrenia. Time of birth in the deficit and nondeficit groups was compared, and time of birth in the deficit group was compared with that for all births in Dumfries and Galloway during the study period.
RESULTS: The deficit schizophrenia group had an excess of summer births, compared to both the nondeficit schizophrenia group and all births in Dumfries and Galloway. The difference between the deficit and nondeficit schizophrenia groups remained significant after accounting for demographic characteristics and symptoms of disorganization and hallucinations plus delusions. A measure of negative symptoms (as opposed to deficit schizophrenia) was a weaker predictor of summer birth.
CONCLUSIONS: This study confirmed an association between deficit schizophrenia and summer birth in the nontropical regions of the Northern Hemisphere. The existence of a risk factor for deficit but not nondeficit schizophrenia is also consistent with other evidence that the pathophysiology of deficit schizophrenia differs from that for other types of the disorder.