Familial risk factors and the familial aggregation of psychiatric disorders

SynopsisAll major psychiatric disorders aggregate in families. For most disorders, both genes and environmental factors play an important role in this aggregation. While recent work has tended to concentrate on the importance of genetic factors, this report focuses on the potential importance of environmental risk factors which themselves aggregate in families. In particular, this article examines how much of the familial aggregation of a psychiatric disorder may result from the familial aggregation of a risk factor. The model is illustrated and then applied to putative familial risk factors for schizophrenia and depression. The results of the model suggest that if parental loss and exposure to pathogenic rearing practices are true risk factors for depression, then they could account for a significant proportion of the familial aggregation of depression. By contrast, the model predicts that even if obstetric injury and low social class are true risk factors for schizophrenia, they together would account for only a very small proportion of the tendency for schizophrenia to aggregate in families.