Schulsinger et al. (1979): Adoption Study: Rates of Suicide in Biological Versus Adoptive Relatives of Adoptees who Committed Suicide and of Live Adoptee Controls*
Three adoption studies have been conducted, all using the same Danish adoption registry. Kety et al., in a study designed to examine the genetics of schizophrenia and mood disorders, found a non-significant trend towards higher concordance for suicide in biological, compared to adoptive relatives of adoptees who committed suicide (2
). Subsequently, a second study compared the rates of suicide among the biological and adoptive relatives of adoptees who committed suicide vs. biological and adoptive relatives of a matched living adoptee control group in Denmark (3
). This study found a six-fold higher rate of suicide in the biological relatives of the suicide vs. those of the control adoptees, and an absence of suicide among the adopted relatives of the suicide vs. control adoptees supporting a genetic rather than environmental etiology (see ). The rate of suicide was higher in the biologic relatives of suicide adoptees regardless of whether the adoptees were psychiatric patients or not. However, it was not possible to determine if the genetic liability to suicide was attributable to the transmission of major psychiatric disorders or to a suicide diathesis per se
In a third adoption study using this registry, a comparison of biological and adoptive relatives of adult adoptees with mood disorder and matched unaffected adoptees were examined (4
), revealed a 15-fold increase in suicide among the biological relatives of the mood-disordered adoptees vs. those of the unaffected adoptees (4
). This finding supports the role of mood disorder in the genetics of suicide. However, the greatest increased risk for suicidal behavior was found in the relatives of those probands with “affect reaction,” a diagnosis akin to borderline personality disorder, suggesting that impulsive-aggressive personality traits may play a role in familial aggregation of suicidal behavior (see ).
Incidence of Suicide in Biological Relatives of Depressive and Control Adoptees*
Taken together, these studies support a strong role for genetics in explaining the familial concordance of completed suicide. Limitations of these studies include restriction to data gathered through routine medical records, and lack of systematic assessment of suicide attempts as well as completions. Thus, while these studies show there are genetic factors explaining the familial aggregation of suicide, they do not shed a great deal of light on what factors might be involved in familial transmission.