title: Genetic and familial environmental effects on suicide--an adoption study of siblings.
abstract: BACKGROUND
  While there is clear evidence of familial influences on suicide, the origin of these is less certain. We have investigated genetic and familial environmental factors by studying the occurrence of suicide in biological and adoptive siblings of adoptees who died by suicide compared to siblings of surviving adoptees.
  
  
  METHODS
  We used the Danish Adoption Register and Danish population registers to compare 221 siblings of adoptees who died by suicide with the siblings of 1,903 adoptees who did not die by suicide. All adoptions in the Danish Adoption Register are non-familial, i.e. the adoptive parents are biologically unrelated to the adoptee. Analyses were conducted on incidence rates of suicide in biological and adoptive siblings given occurrence of suicide in the adoptees while also taking into account psychiatric disorders.
  
  
  RESULTS
  The risk of suicide in full siblings of adoptees who died by suicide before age 60 years was significantly higher than in full siblings of adoptees who had not died by suicide (incidence rate ratios (IRR) = 5.01; 95% confidence interval [CI] = 1.28-19.6). This increase persisted after adjustment for history of psychiatric admission of siblings (IRR = 4.19; 95% CI = 1.00-17.5).
  
  
  CONCLUSIONS
  Genetic factors influence risk of suicide, probably independently of psychiatric disorder. This is relevant in provision of advice to families, including possible prevention of suicide.
authors.affiliation: Institute of Preventive Medicine, Bispebjerg and Frederiksberg Hospital, Capital Region, Copenhagen,  2: National Centre for Register-based Research, University of Aarhus, Aarhus, Denmark.
authors.forename: Liselotte
authors.initials: L
authors.lastname: Petersen
authors.forename: Thorkild I A
authors.initials: TI
authors.lastname: Sørensen
authors.forename: Per Kragh
authors.initials: PK
authors.lastname: Andersen
authors.forename: Preben Bo
authors.initials: PB
authors.lastname: Mortensen
authors.forename: Keith
authors.initials: K
authors.lastname: Hawton
mesh_terms: D020022:Genetic Predisposition to Disease; D006801:Humans; D035781:Siblings / Q000523:psychology*; D013405:Suicide / Q000523:psychology* / Q000706:statistics & numerical data*