Assortative mating in schizophrenia: results from the Copenhagen High-Risk Study.

Assortative mating denotes a tendency for mated pairs to be more similar for some phenotypic trait (similar constitution) than would be the case if the choice of a partner occurred at random. Assortative mating occurs for a variety of physical (e.g., anthropometric variables) and psychological traits (e.g., IQ), including mental illness (Vandenberg 1972). Several studies have shown an excess of married couples suffering from a variety of psychiatric syndromes as compared to the frequency expected on the basis of noncontingent admissions into treatment facilities (Kreitman 1962, 1964, 1968; Nielsen 1964), a finding confirmed in a community study by Hagnell and Kreitman (1974). A recent review of the research literature (Merikangas 1982) concluded that there exists a true primary assortative mating for mental illness. This conclusion is strongly supported by the demonstration of an increased prevalence of mental disorders in the spouses' first-degree relatives (Slater and Woodside 1951; Guze et al. 1970; Cloninger et al. 1975; Gershon et al. 1973; Merikangas et al., in this issue.