Genetic hypotheses and environmental factors in the light of psychiatric morbidity in the families of schizophrenics.
The hypothesis that schizophrenia and some non-psychotic abnormalities occurring in the close relatives are both manifestations of a unitary "schizoid state' due to a major dominant gene is further examined. Comparisons are made (1) of the observed and expected frequencies of the different types of parent mating; and (2) of the observed and expected risks among sibs in families with neither, or with one or both, of the parents abnormal. It is concluded that the results do not fit well with the model of inheritance of the schizoid state through a major dominant gene. Since some hereditary contribution in schizophrenia can be regarded as established, the excess of personality disorders and heavy drinking in the families is thought to be due to a combination of polygenic inheritance and environmental influences. The findings are regarded only as tentative, but suggest several hypotheses which could be tested.