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Data on schizoaffective illness, schizophrenia and affective disorders were gathered on first-degree relatives of schizoaffective probands and matched controls (bipolars, unipolars and schizophrenics). The familial pattern of affective and schizophrenic subtypes of schizoaffective disorder resembled the familial pattern of affective and schizophrenic probands, respectively. The overall risk for the spectrum of schizoaffective and affective disorders was higher among relatives of schizoaffective-manic as compared to relatives of schizoaffective-depressive probands, although the difference fell short of significance. When tested for consistency with multiple threshold hypotheses of genetic transmission, schizoaffective illness did not qualify as either a more extreme form of affective illness nor as a disorder that occupies an intermediate position between bipolar and unipolar disorders or is genetically milder than affective disorder. The implications of diagnostic subtyping for genetic research in the major psychoses were discussed.

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To test the hypothesis that schizophrenia can be differentiated on the basis of family history, the authors compared two matched samples of 20 patients each, distinguished by the presence or absence of family history of schizophrenia. Family history was not associated with either onset characteristics, symptom picture, phenomenological subtypes of schizophrenia, prognostic indicators or global assessment score for psychosocial functioning.

Age-of-onset data were gathered on 93 chronic schizophrenic probands and 57 affected (mainly schizotypal) siblings. 55% of affected individuals were ill before age 20 and 14% had their onset before age 14. The risk period for schizophrenia and schizotypal personality disorders terminated at age 40. Age-of-onset did not distinguish paranoid from nonparanoid schizophrenics, or definite from probable schizotypal personalities. Schizophrenic and schizotypal subjects were similar in their age-of-onset patterns. Sex effect on age-of-onset was not present. A square-root normal distribution gave the best fit to the data. The implications of these findings for schizophrenia research were discussed.

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