With the advent of modern medical research and understanding of disease processes, genetics have been implicated as an important factor in diseases and psychiatric disorders. Genetic mutation and alteration through extensive medical research have been proven beyond doubt as an important factor in suicide attempts. This can be explained by the increased risk of suicide amongst family members with a history of suicide. Different studies have been carried out to this effect and this paper is a review of available studies on the relationship between genetics and suicide.
Extensive clinical studies have been carried out on the role of genetics in suicide, and these studies have shown a positive correlation as family history of suicide raises the risk of suicidal behavior in psychiatric patients. A study in 748 patients, 37 (4.9%) reported a definite suicide attempt in first-degree family members and in 25 (68%) of the affected 37, it was an affective disorder. In another study, 5845 admitted psychiatric patients, 243 (4.2%) had a family history of suicide and more than half of the affected 243 had a primary diagnosis of an affective disorder. Similarly, 100 patients out of the admitted 342 patients with major depressive symptoms have attempted suicide compared to 9 of 80 patients with no family history of suicide.
In the Amish study, 26 suicides occurred over 100 years in a community of Lancaster County in Pennsylvania. 24 of the 26 suicides had major affective disorder and three-quarter of the suicides clustered within 4 families with a pedigree history of suicides. This study went ahead to prove the relationship between family history and the risk of suicide.
Twins sharing similar genetic composition and as such, a risk of suicide is higher amongst twins because of similar genes. The risk is even higher in monozygotic (identical) twin pairs than in dizygotic pair (fraternal). A study reported a statistically significant suicide difference between the twin groups. 9 twin pair had committed suicide from 176 twin pair with seven from the 62 monozygotic twin pair and 2 from the 114 dizygotic twins. Other studies also concluded that suicide risk is higher in the second twin of a monozygotic twin pair than in a dizygotic pair.
Other studies reviewed the association between adoption and risk of suicide. In 548 adoptions, 57 went ahead to commit suicide. Further study revealed that 12 out of the 269 biological relations of the 57 adopted suicides had committed suicides. Results obtained from similar studies went ahead to conclude that genetics play a role in suicide hence the higher incidence amongst family members irrespective of family upbringing and an environment.
Molecular genetic studies have also implicated a variant of Tryptophan Hydroxylase (TH), an enzyme responsible for the synthesis of serotonin (a neurotransmitter that control behavior). A study revealed that 34 of the 36 patients who attempted suicide had either the UL of LL genotype hence a conclusion that the L allele is responsible for suicidal attempts. Further evaluation showed a much higher risk in patients with LL genotype than in UL genotype. The U allele gave some protection against suicidal tendency. In twin pair, 17 twin suicides with established genotype had seven with LL; nine with UL and just one with UU genotype hence further buttressing the association of L allele to suicide.
Other studies revealed significant association between low blood platelet monoamine oxidase (MAO) levels, change in serotonin receptors and transporters and polymorphism in TPH alleles with suicide.
From available data, genetics play a significant role in patients at risk of suicides. However, other factors like stress, environment, and the presence of major psychiatric disorder influence the rate of occurrence of suicides.
You have just read a summary of the research paper: Roy, A., Nielsen, D., Rylander, G., Sarchiapone, M., & Segal, N. (1999). Genetics of suicide in depression. Journal of Clinical Psychiatry, 60, 12-20. Full-text pdf here.