Psychological Medicine

  • Psychological Medicine / Volume 41 / Issue 12 / December 2011, pp 2527-2534
  • Copyright © Cambridge University Press 2011 The online version of this article is published within an Open Access environment subject to the conditions of the Creative Commons Attribution-NonCommercial-ShareAlike licence <>. The written permission of Cambridge University Press must be obtained for commercial re-use.
  • DOI: (About DOI), Published online: 01 June 2011

Original Articles

Familial clustering of suicide risk: a total population study of 11.4 million individuals

D. Tidemalma1 c1, B. Runesona1, M. Waerna2, T. Frisella3a4, E. Carlströma3, P. Lichtensteina3 and N. Långströma3a4

a1 Department of Clinical Neuroscience, Karolinska Institutet, Division of Psychiatry, Stockholm, Sweden

a2 Institute of Neuroscience and Physiology, Section of Psychiatry and Neurochemistry, Sahlgrenska Academy at Göteborg University, Göteborg, Sweden

a3 Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden

a4 Centre for Violence Prevention, Karolinska Institutet, Stockholm, Sweden


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.

Method 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.

(Received December 03 2010)

(Revised April 28 2011)

(Accepted April 30 2011)

(Online publication June 01 2011)


c1 Address for correspondence: Dr D. Tidemalm, Department of Clinical Neuroscience, Karolinska Institutet, Division of Psychiatry, St Göran, SE-112 81 Stockholm, Sweden. (Email: