Medline ® Abstracts for References 58,61

All suicides were ascertained for a 100-year period (1880 to 1980) in a study of mental illness among the Old Order Amish. The majority (92%) of the 26 cases were diagnosed with a major affective disorder and were situated in multigenerational families with heavy loading for bipolar, unipolar, and other affective-spectrum illnesses. The suicides clustered in four primary pedigrees, and the role of inheritance was suggested by the way in which suicides followed the distribution of affective disorders in these kinship lines. We believe these extended pedigrees provide presumptive evidence of genetic factors in both suicides and affective disorders.

Suicide appears to cluster in families, suggesting that genetic factors may play a role in this behavior. We studied 176 twin pairs in which one or both twins had committed suicide. Seven of the 62 monozygotic twin pairs were concordant for suicide compared with two of the 114 dizygotic twin pairs (11.3% vs 1.8%). The presence of psychiatric disorder in the twins and their families was examined in a subsample of 11 twin pairs, two of whom were concordant for suicide. Eleven of these 13 twin suicide victims had been treated for psychiatric disorder, as had eight of their nine surviving cotwins. In addition, twins in 10 pairs had other first- or second-degree relatives who had been treated for psychiatric disorder. Thus, these twin data suggest that genetic factors related to suicide may largely represent a genetic predisposition for the psychiatric disorders associated with suicide. However, they leave open the question of whether there may be an independent genetic component for suicide.