Winter birth and biological family history in adopted schizophrenics

To investigate relationships between birth season and biological family history in schizophrenia, this study used a sample of schizophrenics that had the advantages of (a) particularly thorough diagnostic assessments of schizophrenics' relatives, including information from direct interviews as well as chart reviews, and (b) schizophrenic probands who were adopted at early age, mitigating the usual confounding of genetic and postnatal environmental influences of the family. Adopted schizophrenics with no biological family history of schizophrenia-spectrum disorders were significantly more likely to be born in winter months than were either (a) their own biological relatives, including their sibs and half-sibs, (b) schizophrenics with a positive family history for schizophrenia-spectrum disorders, or (c) people in the general population. Family-history-positive schizophrenics and their schizophrenic relatives were, in turn, significantly less likely than their own non-schizophrenic biological relatives to be born in the winter; schizophrenics in these families tended to be born in the milder-weather seasons, particularly the spring and fall. Results suggest that environmental factors associated with winter birth may be etiologically important in schizophrenia, particularly for cases in which familial liability factors are weak. By contrast, a familial, probably genetic, liability factor may be especially important in schizophrenics born in mild weather.

Inverse relationship of perinatal complications and eye tracking dysfunction in relatives of patients with schizophrenia: evidence for a two-factor model

OBJECTIVE

Because both smooth pursuit eye tracking dysfunction and obstetrical complications are significant risk factors for schizophrenia, the authors tested the predictions of a two-factor model of how eye tracking dysfunction and obstetrical complications covary in patients with schizophrenia, their siblings, and comparison subjects.

METHOD

Psychiatric diagnoses, eye tracking dysfunction, and obstetrical complications noted in birth records were independently assessed in 18 patients with schizophrenia, 16 of their siblings without schizophrenia, and 49 comparison subjects with neither personal nor family histories of schizophrenia.

RESULTS

As hypothesized, 1) the combination of eye tracking dysfunction and perinatal obstetrical complications discriminated patients with schizophrenia significantly from subjects without schizophrenia, including siblings of patients with schizophrenia, and 2) eye tracking dysfunction and perinatal obstetrical complications manifested a significant inverse association in the nonschizophrenic siblings of patients with schizophrenia.

CONCLUSIONS

These results support a two-factor model in which obstetrical complications often interact with genetic liability, indicated by eye tracking dysfunction, to produce schizophrenia.