abuse may be transmitted across generations, since non-abused children of sexually abused parents have increased suicidal behaviors (Brent et al., in press). Additional research is needed to sort out these issues.
Several lines of evidence point to a link between genetic inheritance and risk of suicide. The following sections describe some of that evidence that derives from adoption studies, twin studies, family studies, candidate genes, and a new microarray approach.
Schulsinger et al. (1979) conducted a record linkage study among Danish adoptees, and found that the rate of suicide in the biological relatives of adoptees who had completed suicide was 6-fold higher than the rate in the biological relatives of living adoptees. There was no elevation of the rate of suicide in the adoptive relatives. This study strongly supports a genetic component to suicide, although it is less informative on exactly what is being transmitted—psychopathology or some other liability. It also argues against imitation.
A second adoption study examined the risk of suicide in the biological and adoptive relatives of adoptee probands who had a mood disorder (Wender et al., 1986). Interestingly, the highest rate of suicide was in the biological relatives of those probands with a diagnosis of “affect reaction,” which roughly corresponds to borderline personality disorder. This rate (7.6 percent) was almost 3 times higher than the rate of suicide in the biological relatives of those with unipolar depression (2.2 percent), suggesting that the familial transmission of suicidal behavior might be more closely related to the transmission of difficulty with regulation of affect and impulses than mood disorder per se. An analysis of this study (Abbar et al., 1996) concluded that the genetic susceptibility to suicide was transmitted independently of the transmission of personality disorder.
Juel-Nielsen and Videbech (1970) showed that monozygotic (identical) twins showed greater concordance for suicide than did dizygotic (fraternal) twins. Roy and colleagues (1991) updated these results, reviewed the world literature of case reports of twin suicides, and again found a much higher concordance for suicide among monozygotic than dizygotic twins (11.3 percent vs. 1.8 percent), consistent with a genetic etiology, most likely polygenic. In a subsequent study, Roy et al. (1995)