Genetic and environmental factors in pain symptoms and self-harm, and their association. A twin study

Individuals who self-harm are often insensitive to pain, and consequently pain sensitivity has been proposed as a barrier for self-harm. It is unclear how pain and self-harm interplay in real life settings, and to what extent genetics and environmental factors contribute to the etiology of both. This study was registry based using classical twin design. A cohort of 16 948 Swedish twin pairs born between 1992 and 2010, was prospectively assessed for pain symptoms at ages 9 and 18, and followed up for later self-harm until 2016 and a maximum age of 24. The relative contributions of genetic and environmental factors to each phenotype were estimated using univariate twin models. Logistic regression models assessed their association, and conditional models adjusted for familial confounding. Genetics and non-shared environment contributed to pain and self-harm to a moderate degree at both age 9 and age 18, while the contribution of shared environment was small for both pain and self-harm at both ages. At age 18 the pain symptoms group had higher odds for later self-harm (odds ratio 1.59, 95% CI 1.06-2.41, p = .003), and pain seemed to be partially in the causal pathway as it was not explained by familial confounding. This study adds to the evidence of pain symptoms as a predictor for self-harm.