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| Risk Factors
> Genetics |
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Twin, Family and Adoption Studies
Adoption and family studies have reported that suicidal behavior has a genetic component that is independent of the heritability of major psychiatric disorders. Twin studies have reported much higher concordance rates for suicidal acts in identical vs non-identical twins (13.2% vs 0.7%), and the rate of suicide in identical twins is over 3 times the expected rate. A higher concordance rate for suicide attempt has also been reported in identical vs non-identical twins who survive the co-twin’s suicide indicating that attempted and completed suicide are both heritable components of the phenotype of suicidal behavior. The largest twin study to date reported a 23.1% concordance rate for a serious suicide attempt in identical twins that was 17-fold greater than the risk compared to the total sample, and represented a heritability of 55%.
Candidate Genes
The search is now on for the genes which may be responsible for the heritablity of suicidal behavior, including studies incorporating surveys of the entire genome, as well as studies exploring candidate genes related to components of the serotonin system. For example, tryptophan hydroxylase is the rate-limiting enzyme for the biosynthesis of serotonin, and this gene has two polymorphisms (possible genetic variants). Some evidence suggests that both suicidal acts and indices of serotonin function are associated with a particular polymorphism of this gene. Other studies have examined the genes regulating different components of the serotonin system including various serotonin receptor subtypes as well as studying the gene that regulates the re-uptake of serotonin into nerve endings (serotonin transporter). The results from these studies to date are inconclusive which may have much to do with studying very small samples with incomplete definition of indices of suicidal behavior. A considerable amount of the variance in serotonergic activity is attributable to genetic factors (heritable paternal variance is 37% and heritable maternal penetrance is 22%). This therefore means that a considerable potential remains for environmental factors to influence serotonergic activity.
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Suicide: Facts and Fiction
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Fact
Most people who kill themselves have given definite w ...
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