Assortative mating in the affective disorders: a systematic review and meta-analysis

Assortative mating, or the tendency for individuals with similar phenotypes to mate more frequently than expected by chance, has been reported for a variety of complex traits, including many neuropsychiatric disorders. Although assortative mating has been reported in affective disorders, the studies done to date have been inconclusive. This study attempts to assess the degree of assortative mating in individuals with affective disorders using systematic review and meta-analytic techniques. Studies on assortative mating in affective disorders were identified by a computerized literature search and by bibliographic assessment of published studies and reviews. Studies were selected if they had a case-control design and if they reported rates of affective disorders in the spouses of probands and controls. Of the 17 studies reviewed, six were selected for meta-analysis. All studies were blinded. Details of study design, patient characteristics, and rates of affective disorders were assessed by two independent reviewers. Twelve of the 17 studies assessed reported an increase in assortative mating. Results of the meta-analysis supported these findings, and indicated that assortative mating occurs in both bipolar disorder and major depression. Although most studies examined reported an increase in assortative mating among individuals with affective disorders, the degree of assortative mating reported varied widely. Meta-analysis with six controlled studies showed evidence for assortative mating, and suggested that the degree of assortative mating is higher for individuals with bipolar disorder than for those with major depression. These results support the previously reported findings, and may have important implications for genetic studies.