Summer birth and deficit schizophrenia: Cantabria, Spain.

An association between deficit schizophrenia and summer birth has previously been reported. The authors attempted to replicate this association in a population-based study of incident cases of psychosis in the autonomous region of Cantabria, in northern Spain. Schizophrenia patients were categorized into deficit (N = 22) and nondeficit (N = 55) groups, and the pattern in the two groups was compared. After accounting for the variance due to disorganization, hallucinations and delusions, and demographic variables, deficit schizophrenia had a significant association with summer birth; this association did not depend on a single definition of summer. For instance, among the deficit patients, 59% were born from May to August, in contrast to 18% of nondeficit patients and 34% of the general population. These results confirm the association between summer birth in the Northern Hemisphere and deficit as opposed to nondeficit schizophrenia. The existence of a different risk factor for the two groups suggests a difference in etiology and pathophysiology.