title: Familial clustering of suicide risk: a total population study of 11.4 million individuals.
abstract: BACKGROUND
  Research suggests that suicidal behaviour is aggregated in families. However, due to methodological limitations, including small sample sizes, the strength and pattern of this aggregation remains uncertain.
  
  
  METHODS
  We examined the familial clustering of completed suicide in a Swedish total population sample. We linked the Cause of Death and Multi-Generation Registers and compared suicide rates among relatives of all 83 951 suicide decedents from 1952-2003 with those among relatives of population controls.
  
  
  RESULTS
  Patterns of familial aggregation of suicide among relatives to suicide decedents suggested genetic influences on suicide risk; the risk among full siblings (odds ratio 3.1, 95% confidence interval 2.8-3.5, 50% genetic similarity) was higher than that for maternal half-siblings (1.7, 1.1-2.7, 25% genetic similarity), despite similar environmental exposure. Further, monozygotic twins (100% genetic similarity) had a higher risk than dizygotic twins (50% genetic similarity) and cousins (12.5% genetic similarity) had higher suicide risk than controls. Shared (familial) environmental influences were also indicated; siblings to suicide decedents had a higher risk than offspring (both 50% genetically identical but siblings having a more shared environment, 3.1, 2.8-3.5 v. 2.0, 1.9-2.2), and maternal half-siblings had a higher risk than paternal half-siblings (both 50% genetically identical but the former with a more shared environment). Although comparisons of twins and half-siblings had overlapping confidence intervals, they were supported by sensitivity analyses, also including suicide attempts.
  
  
  CONCLUSIONS
  Familial clustering of suicide is primarily influenced by genetic and also shared environmental factors. The family history of suicide should be considered when assessing suicide risk in clinical settings or designing and administering preventive interventions.
authors: Department of Clinical Neuroscience, Karolinska Institutet, Division of Psychiatry, Stockholm, Sweden. dag.tidemalm@ki.se
authors: D
authors: D
authors: Tidemalm
authors: B
authors: B
authors: Runeson
authors: M
authors: M
authors: Waern
authors: T
authors: T
authors: Frisell
authors: E
authors: E
authors: Carlström
authors: P
authors: P
authors: Lichtenstein
authors: N
authors: N
authors: Långström
mesh_terms: D016000:Cluster Analysis; D016208:Databases, Factual; D005190:Family / Q000523:psychology*; D005195:Family Relations; D005260:Female; D006801:Humans; D008297:Male; D012307:Risk Factors; D018454:Spouses / Q000523:psychology / Q000706:statistics & numerical data; D013405:Suicide / Q000706:statistics & numerical data*; D013406:Suicide, Attempted / Q000706:statistics & numerical data; D013548:Sweden / Q000453:epidemiology; D014429:Twins, Dizygotic / Q000523:psychology; D014430:Twins, Monozygotic / Q000523:psychology