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Self- injurious behaviors (SIBs) occur in both people at risk of suicide and in people with intellectual delay, and it may be that the underlying pathologies are shared, at least in part. Genes identified as causative in people with intellectual delay that show SIBs may be the same genes that have an effect on suicide outcome in people without intellectual delay that self-injure.
The prevalence of self-injurious behaviors (SIBs) in the intellectually delayed population ranges from 1.7–41% and this large difference is due mostly to the criteria and setting used to assess SIB's (Rojahn, 1986; Saloviita, 2000). It is not clear why a large portion of people with intellectual delay self-injure, but it does not seem to be a means of communicating anger or frustration as some groups have suggested. For example, a recent study suggests no association between communication impairment and self-injury (Cooper et al., 2009). An alternative possibility is that the genetic alteration(s) leading to intellectual delay also have a role in self-injury. This hypothesis is supported by the association between certain genetic disorders that cause intellectual delay and SIBs. For example, people with Lesch-Nyhan Syndrome (mutations in the gene encoding hypoxanthine-guanine phosphoribosyltransferase), Smith-Magenis syndrome (deletion at 17p11.2), Cornelia de Lange syndrome (variation at the NIPBL gene) or Prader-Willi syndrome (loss of paternal contribution to 15q11-q13 genomic region) have higher frequencies of self-injurious behaviors than other people with intellectual delays, while people with Down syndrome very rarely show SIBs. These examples suggest that specific genes, or interactions of specific genes, may contribute to SIBs possibly by sensitizing or evoking interactions with other genetic variation.
Suicide has long been long known to have a genetic component, where family members are ~3 times more likely to complete suicide if someone in the family has already died by suicide, even after controlling for psychopathology and socioeconomic status, amongst other variables (Brent et al., 1996). Of note, self-injurious behaviors are not uncommon in people who go on to complete suicide (Zahl and Hawton, 2004). The search for genes involved in suicide, however, has proved remarkably challenging to find with any reliability, thus novel strategies to elucidate genetic findings in suicide are needed.
Finding the causative mutation in people with intellectual delay with SIBs is experimentally more feasible than studying the genetics of psychiatric populations that show SIBs, mostly because there is often a clearer link between genotype and phenotype in the intellectually delayed. While these mutations can be broad - large segmental deletions for example, they could narrow down some genes that could be involved in SIBs more generally. While multiple genes are likely involved in suicide, studying or identifying genes implicated in self-injury from patients with intellectual disability could help guide genetic studies in suicide research.
CE is funded by a Canadian Institute for Health Research fellowship.
Statement of Interest: None