Personality As an Endophenotype for Molecular Genetic Investigations Jonathan B

Research in Translation Trends in Suicidology: Personality as an Endophenotype for Molecular Genetic Investigations Jonathan B. Savitz*, Cinda-Lee Cupido, Rajkumar S. Ramesar sychopathology, especially depression, is the most important Prisk factor for suicidal behaviour [1,2] with between 25% and 40% of depressed patients attempting suicide [3] and about 3.4% completing suicide eventually [4]. Given recent fi gures suggesting that the lifetime prevalence of a major depressive episode among the US population is 32.6–35.1 million [5], it is no surprise that suicide ranks among the top ten causes of death in many other countries [6]. Understanding the aetiology of a signifi cant public health issue such as suicide is important but diffi cult because of its complex and multifactorial origins. Although most suicidal behaviour occurs within the context of a mood disorder, most depressed individuals never attempt suicide. Furthermore, no linear relationship between the severity of the DOI: 10.1371/journal.pmed.0030107.g001 depressive episode and the likelihood Colours of Depression of suicide has been forthcoming [7], (Illustration: Raj Ramesar) highlighting the importance of other Funding: The authors received no specifi c funding factors in addition to psychiatric for this article. At the family level, the risk of illness. These factors include substance Competing Interests: The authors declare that they abuse or alcoholism, a head injury, a suicide is higher in individuals with have no competing interests. dysfunctional family or childhood abuse a family history of suicide [16,17], and the suicide rate of adolescents Citation: Savitz JB, Cupido C-L, Ramesar RS [8], high rates of gun ownership [9], (2006) Trends in suicidology: Personality as an smoking [10], socioeconomic adversity is highly correlated with the suicide endophenotype for molecular genetic investigations. [11], and personality factors [12]. rate among their relatives [18]. Even PLoS Med 3(5): e107. Genetic factors may also be very studies that have controlled for levels DOI: 10.1371/journal.pmed.0030107 important [13,14]. Marusic and Farmer of psychopathology have shown that relatives of suicide completers and Copyright: © 2006 Savitz et al. This is an open-access [15] argue that the variation in the article distributed under the terms of the Creative suicide rate across European countries attempters are at an increased risk for Commons Attribution License, which permits (7–43 per 100,000 inhabitants per year) suicidal behaviour [19,20]. Twin studies unrestricted use, distribution, and reproduction in indicate that this familial clustering of any medium, provided the original author and source cannot be explained by sociocultural are credited. factors alone and is probably due to suicidal behaviour has a partly genetic basis with heritability estimates of 17%– Abbreviations: COMT, catechol-O-methyl- shared genetic vulnerability. A case transferase; EPQ, Eysenck Personality Questionnaire; in point is the high suicide rate in 55% for suicidal behaviour [21,22] FFM, Five-Factor Model inventory; MAO-A, Hungary and Finland, two populations and 20% for suicide [23] reported. monoamine oxidase A; SERT, serotonin transporter; The only adoption study we are aware TCI, Cloninger’s Temperament and Character with a common genetic origin but Inventory; TPH, tryptophan hydroxylase with divergent cultural and political of suggested that as far as suicidal trajectories [15]. behaviour is concerned, adoptees Jonathan B. Savitz, Cinda-Lee Cupido, and Rajkumar resemble their biological parents more S. Ramesar are at the UCT/MRC Human Genetics Research Unit, Institute of Infectious Disease and than the adoptive family [24]. Molecular Medicine, University of Cape Town, Cape Research in Translation discusses health interventions These data have catalysed the Town, South Africa. in the context of translation from basic to clinical search for genes that predispose to research, or from clinical evidence to practice. * To whom correspondence should be addressed: suicidal behaviour, with more than E-mail: [email protected] PLoS Medicine | www.plosmedicine.org 0619 May 2006 | Volume 3 | Issue 5 | e107 A rich body of data details the Table 1. Association Analyses of Genes Predisposing to Suicide or Suicidal Behaviour association between suicide attempts Gene OMIM Locus Association Evidence and impulsivity. Impulsivity has been Serotonin transporter 182138 17q11.2 7 + and 7 − studies, 2 + meta- shown to be a risk factor for suicidal analyses behaviour in a variety of adults Tryptophan hydroxylase 191060 11p15-14 5 + and 7 − studies, 2 + meta- [7,8,28–30] and adolescents [11,31,32] analyses and 1 − meta-analysis with psychiatric illness, in a forensic Monoamine oxidase A 309850 Xp11.23 3 + and 2 − studies psychiatric population [33], and in the Serotonin receptor 1A (5-HT1A) 109760 5q11.2-q13 1 + and 2 − studies general population [34]. Serotonin receptor 1B (5-HT1B) 182131 6q13 1 + and 5 − studies Serotonin receptor 2A (5-HT2A) 182135 13q14.2 3 + and 9 − studies, 1 − meta- Freud regarded suicide as an analysis aggressive act, a view borne out to Catechol-O-methyltransferase (COMT) 116790 22q11.21 3 + and 2 − studies some extent by modern data. Simon Dopamine receptor 2 (DRD2) 126450 11q23 1 + study and 1 − study et al. [35] found that involvement Dopamine receptor 4 (DRD4) 126452 11p15.5 2 − studies in physical fi ghts was associated with violent suicide attempts, and, according + and − indicate positive and negative studies published. DOI: 10.1371/journal.pmed.0030107.t001 to Appleby et al. [36], people who committed suicide were more likely 100 studies now published [25]. environmental factors—then the to have been arrested in the previous Post-mortem studies of people who endophenotype is a more elementary six months. Cavanagh et al. [37] committed suicide have led to the trait that is tightly correlated with confi rmed that a criminal record is general consensus that a disturbance suicide. The genetic architecture of a risk factor for subsequent suicide. of the serotonergic system is associated the endophenotype is assumed to Fulwiler et al. [38] detected a higher with suicidal behaviour. Therefore, it echo its relative phenotypic simplicity, rate of suicide attempts in a group is no surprise that most of the genes presenting a more tractable target for of violent compared with nonviolent implicated in suicidal behaviour—the geneticists. An understanding of the patients with psychiatric illness, and serotonin transporter (SERT), molecular basis of the endophenotype in South Africa conduct disorder was tryptophan hydroxylase (TPH), should theoretically be the fi rst step found to be the most frequently made monoamine oxidase A (MAO-A), and towards the larger prize: uncovering the diagnosis in suicidal adolescents [39]. the serotonin receptors, 5-HTR1A, molecular basis of the phenotype itself. Negative affect or anxiety is most 5-HTR2A, and 5-HTR1B—modulate Gottesman and Gould [27] commonly measured in the form central serotonergic function (see assert that for a biological marker of neuroticism from the Eysenck Table 1). As is the case with most to be classifi ed as a bona fi de Personality Questionnaire (EPQ) complex traits, however, success tends endophenotype, it must meet the or the Five Factor Model (FFM) to plateau at a point where good following conditions: 1) be associated inventory (see Glossary). Neuroticism candidate genes are identifi ed but with the illness in the relevant is a higher order trait that measures conclusive causal inferences remain population; 2) be largely state- a predisposition to experience anger, elusive because of replication failures. independent, manifesting in the anxiety, depression, guilt, and other The unequivocal identifi cation of individual during both periods of negative emotions or cognitions. genes related to psychiatric disorder health and illness; 3) be heritable; 4) A signifi cant relationship between is retarded by a complex interplay within families, the endophenotype neuroticism and suicidal ideation of latent environmental infl uences and illness should co-segregate; 5) if has been regularly demonstrated or gene–environment interactions; found in affected individuals should [11,22,40,41], and the same holds true genetically and phenotypically also be found in nonaffected family for neuroticism and attempted suicide heterogeneous samples; the possible members at a higher rate than in the [28,42–46]. High levels of anxiety or effects of numerous loci of small effect general population. negative affectivity have been equally size; and the diffi culty of adequately In the following sections we use implicated in completed suicide [47– correcting for multiple testing. Faced 50]. Gottesman and Gould’s [27] fi ve with these frustrations, the use of A number of studies have reported criteria above to evaluate the latest endophenotypes as an aid to molecular introversion to be associated with trend in suicide research: the merits genetic investigations has become suicidal thoughts and behaviour of using an endophenotype such almost de rigueur. In the case of [42,51–53]. In two psychological as personality to identify suicide suicide, a number of researchers have autopsies of completed suicides, susceptibility genes. advocated the use of personality traits Duberstein et al. [50] detected lower as endophenotypes [12,26]. Are Specifi c Personality Traits levels of extraversion in their cohort, and Maser et al. [53] found that Associated with Suicide What Is

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