Background:
Seasonal asymmetry of schizophrenia births is a well-documented phenomenon, with most studies finding a winter/early spring excess. This effect is consistent in the northern hemisphere but rare in the southern hemisphere. In Western Australia, using an endophenotype-based approach, we delineated a discrete, genetically distinct subtype of schizophrenia characterized by pervasive cognitive deficits (CDs), with the residual cases being cognitively spared (CS) (Hallmayer et al. 2005).
Purpose:
We compared birth seasonality in Australian-born patients with CD and CS subtypes.
Methods:
Data were grouped according to month of birth, with calendar adjustment. Season of birth was calculated using the Kuipers grouped method (Freedman 1979).
Results:
The CD, but not the CS, subtype showed a significant season-of-birth effect, with an autumn peak (April) and a summer trough.
Conclusions:
Analysis of northern hemisphere studies (Messias et al. 2004) found that the deficit syndrome of schizophrenia (Kirkpatrick et al. 2001), sharing some characteristics with our CD subtype, has a peak of summer births, at variance with the winter peak for all schizophrenia. Although the peak for CD is in autumn, it too contrasts with the spring peak of all schizophrenia births in Western Australia (Morgan et al. 2000). Despite numerous studies showing birth seasonality in schizophrenia, its cause remains elusive. Geographical differences in exposure to circannually fluctuating, nongenetic risk factor(s) may underlie this phenomenon (McGrath & Welham 1999). A challenge for future studies is to map the seasonal relationship between schizophrenia endophenotypes and risk factors such as low birth weight.
