Lisa Mariella Loibl

Genetics of suicide: a systematic review of twin studies.

ZusammenfassungHINTERGRUND: Übereinstimmende Befunde aus einer Vielzahl von Forschungsdesigns (Adoptions-, Familien-, Migranten- und Zwillingsstudien sowie Genom-Scans, familiennamenbasierte, geografische und molekulargenetische Studien) weisen auf eine Beteiligung genetischer Risikofaktoren für Suizid hin. Dieser Beitrag bietet einen ausführlichen und aktuellen Überblick über die zu diesem Thema vorhandenen Zwillingsstudien. METHODEN: Über extensive Literatursuche wurden insgesamt 32 Studien (19 Fallberichte, 5 zwillingsregisterbasierte Studien, 4 populationsbasierte epidemiologische Studien, 4 Studien überlebender Ko-Zwillinge) eruiert, die hier zusammengefasst und diskutiert werden. Dieses Literaturkorpus wurde zwischen 1812 und 2006 in 6 verschiedenen Sprachen publiziert und enthält Daten aus 13 Ländern. ERGEBNISSE: Eine Meta-Analyse aller zwillingsregisterbasierten Studien und aller Fallberichte aggregiert zeigt, dass eineiige Zwillinge signifikant häufiger für Suizid konkordant sind als zweieiige Zwillinge. Ausschließlich psychosoziale Erklärungen für diesen Befund werden durch die Ergebnisse von Ko-Zwillingsstudien ausgeschlossen. Populationsbasierte epidemiologische Studien zeigen einen signifikanten Beitrag genetischer Faktoren (geschätzte Heritabilität: 30–55%) für den weitergefassten Phänotyp suizidalen Verhaltens (Suizidgedanken, Suizidpläne, Suizidversuche), der für die verschiedenen Typen suizidalen Verhaltens weitgehend überlappt und von der Vererbung psychiatrischer Erkrankungen weitgehend unabhängig ist. Effekte nicht-geteilter Umwelt (persönliche Lebenserfahrungen) tragen ebenfalls substantiell zum Risiko für suizidales Verhalten bei, nicht jedoch Effekte geteilter Umwelt (Familie). SCHLUSSFOLGERUNG: Die Gesamtheit der Befunde aus Zwillingsstudien zu Suizid legt sehr deutlich eine Beteiligung genetischer Faktoren an der Anfälligkeit zu suizidalem Verhalten nahe. Beschränkungen der Zwillings-Methode, Mängel der Literatur und weitere Punkte werden zur Förderung des Forschungsfortschritts in diesem Bereich ausführlich diskutiert (u.a.: Bias-Quellen und Leerstellen in der Literatur, Fehler in früheren Überblicksarbeiten, Alters- und Geschlechtseffekte sowie Zwillingsbesonderheiten bezüglich Suizidrisiko, wissenschaftsgeschichtlicher Kommentar).SummaryOBJECTIVES: Convergent evidence from a multitude of research designs (adoption, family, genomescan, geographical, immigrant, molecular genetic, surname, and twin studies of suicide) suggests genetic contributions to suicide risk. The present account provides a comprehensive and up-to-date review of the twin studies on this topic. METHODS: A total of 32 studies (19 case reports, 5 twin register-based studies, 4 population-based epidemiological studies, 4 studies of surviving co-twins) located through extensive literature search strategies are summarized and discussed here. This literature corpus was published between 1812 and 2006 in six languages and reports data from 13 countries. RESULTS: A meta-analysis of all register-based studies and all case reports aggregated shows that concordance for completed suicide is significantly more frequent among monozygotic than dizygotic twin pairs. The results of co-twin studies rule out exclusively psychosocially based explanations of this pattern. Population-based epidemiological studies demonstrate a significant contribution of additive genetic factors (heritability estimates: 30–55%) to the broader phenotype of suicidal behavior (suicide thoughts, plans and attempts) that largely overlaps for different types of suicidal behavior and is largely independent of the inheritance of psychiatric disorders. Nonshared environmental effects (i.e. personal experiences) also contribute substantially to the risk of suicidal behavior, whereas effects of shared (family) environment do not. CONCLUSIONS: The totality of evidence from twin studies of suicide strongly suggests genetic contributions to liability for suicidal behavior. To further research progress in this area, an extensive discussion of design limitations, shortcomings of the literature and further points is provided, including sources of bias, gaps in the literature, errors in previous reviews, age and sex effects and twin-singleton differences in suicide risk, and notes from a history-of-science view.

Scientometric Analysis and Bibliography of Digit Ratio (2D:4D) Research, 1998–2008

A scientometric analysis of modern research on the second-to-fourth digit ratio (2D:4D), a widely studied putative marker for prenatal androgen action, is presented. In early 2009, this literature totalled more than 300 publications and, since its initiation in 1998, has grown at a rate slightly faster than linear. Key findings included evidence of publication bias and citation bias, incomplete coverage and outdatedness of existing reviews, and a dearth of meta-analyses in this field. 2D:4D research clusters noticeably in terms of researchers, institutions, countries, and journals involved. Although 2D:4D is an anthropometric trait, most of the research has been conducted at psychology departments, not anthropology departments. However, 2D:4D research has not been predominantly published in core and specialized journals of psychology, but rather in more broadly scoped journals of the behavioral sciences, biomedical social sciences, and neurosciences. Total citation numbers of 2D:4D papers for the most part were not larger than their citation counts within 2D:4D research, indicating that until now, only a few 2D:4D studies have attained broader interest outside this specific field. Comparative citation analyses show that 2D:4D research presently is commensurate in size and importance to evolutionary psychological jealousy research, but has grown faster than the latter field. In contrast, it is much smaller and has spread more slowly than research about the Implicit Association Test. Fifteen conjectures about anticipated trends in 2D:4D research are outlined, appendixed by a first-time bibliography of the entirety of the published 2D:4D literature.

Consistency of immigrant and country-of-birth suicide rates: a meta-analysis

Objective:  Multifaceted evidence (family, twin, adoption, molecular genetic, geographic and surname studies of suicide) suggests genetic risk factors for suicide. Migrant studies are also informative in this context, but underused. In particular, a meta‐analysis of the associations of immigrant (IMM) and country‐of‐birth (COB) suicide rates is unavailable.

Testing the Finno-Ugrian Suicide Hypothesis: Replication and Refinement with Regional Suicide Data from Eastern Europe

Multiple lines of evidence indicate specific genetic contributions to suicidal behavior. In particular, geographic studies support the Finno-Ugrian Suicide Hypothesis, i.e., genetic differences between populations may partially account for geographic patterns of suicide prevalence. Specifically, within Europe the high suicide-rate nations constitute a contiguous J-shaped belt. The present research replicated and extended 2003 findings of Voracek, Fisher, and Marušič with new data. Across 37 European nations, an interaction term of squared latitude multiplied with longitude (quantifying the J-shaped belt) accounted for 32% of the cross-national variance in total suicide rates alone, while latitude accounted merely for 18% of variance over and above those. Refined analysis included regional data from countries critical for testing the hypothesis (89 regions of Belarus, western Russia, and the Ukraine) and yielded an even more clear-cut pattern (56% and 3.5%, respectively). These results are consistent with the Finno-Ugrian Suicide Hypothesis. Study limitations and directions for further research are discussed.

Consistency of immigrant suicide rates in Austria with country-of-birth suicide rates: a role for genetic risk factors for suicide?

Multifaceted evidence (family, twin, adoption, molecular genetic, geographic, and surname studies of suicide) suggests genetic risk factors for suicide. The migrant study design is also informative in this context, but underused. In particular, immigrant studies of suicide with a continental European host country are unavailable. The correspondence of suicide prevalence among 22 immigrant groups in Austria (1970-2006) with those of the homelands during the same period was analyzed. Immigrant and homeland suicide rates were significantly positively associated. Controls for age of suicide victim, immigrant group size, national pride, and quality of life in the homelands left the finding essentially unchanged. This correspondence of immigrant and country-of-birth suicide rates is consistent with the assumption of population differences in the prevalence of genetic risk factors for suicide, for which there is emerging evidence.

The contributions of Hans-Dieter Rösler: pioneer of digit ratio (2D:4D) research.

Over the past decade, the second-to-fourth digit ratio (2D:4D), a putative biomarker for the organizational (permanent) effects of prenatal androgens on the human brain, body, and behavior, has received extensive research attention in psychology. This account makes more widely accessible the contributions of the German psychologist, Hans-Dieter Rösler, an early, for a long time unnoticed, predecessor of modern 2D:4D research. In the mid-1950s, Rösler collected a massive sample of hand outline drawings, totalling nearly 7,000 individuals, ranging in age from 1 mo. to 70 yr. With regard to the distal finger-extent pattern, Rösler differentiated radial (longer index than ring finger), ulnar (reversed pattern), and intermediate hand types, which reflect higher (more female-typical), lower (more male-typical), and intermediate 2D:4D, respectively. Here is summarized Röslers research. In a series of investigations into the hand types, he reported on their anatomical bases, unsuitability for paternity testing, developmental changes, heritability, sex, side, and occupational group differences, and associations with left-handedness, manual dexterity, mental retardation, and clinodactyly. Based on new data from 313 male and 316 female adults, hand type is further shown to be only a weak proxy of actual 2D:4D, leaving 75% of the interindividual variation in 2D:4D unexplained. Notwithstanding these shortcomings of the hand-type method, Röslers work from the 1950s still has the potential to inform modern 2D:4D research, as it contains a multitude of testable hypotheses not yet picked up by current research.

Beliefs about the genetics of suicide in Canadian students: cross-language validation of the Beliefs in the Inheritance of Risk Factors for Suicide Scale (BIRFSS)

Aim:  The genetics underlying suicidal behavior is becoming increasingly recognized and investigated. Convergent evidence towards this end has emerged from numerous research strategies (adoption, family, genome‐scan, geographic, immigrant, molecular genetic, surname, and twin studies of suicide). The topic‐related mental‐health literacy (i.e. knowledge and beliefs) of professionals and laypersons, however, may lag behind this research progress, and data on this question are scant. The aim of the present study was therefore to further validate, in a cross‐language setting, the novel 22‐item Beliefs in the Inheritance of Risk Factors for Suicide Scale (BIRFSS), originally developed in German, which assesses beliefs about the genetics of suicide.

The Beliefs in the Inheritance of Risk Factors for Suicide Scale (BIRFSS): Cross-Cultural Validation in Estonia, Malaysia, Romania, the United Kingdom, and the United States

The genetics of suicide is increasingly recognized and relevant for mental health literacy, but actual beliefs may lag behind current knowledge. We examined such beliefs in student samples (total N = 686) from Estonia, Malaysia, Romania, the United Kingdom, and the United States with the Beliefs in the Inheritance of Risk Factors for Suicide Scale. Cultural effects were small, those of key demographics nil. Several facets of construct validity were demonstrated. Marked differences in perceived plausibility of evidence about the genetics of suicide according to research design, observed in all samples, may be of general interest for investigating lay theories of abnormal behavior and communicating behavioral and psychiatric genetic research findings.

Beliefs in genetic determinism and attitudes towards psychiatric genetic research: psychometric scale properties, construct associations, demographic correlates, and cross-cultural comparisons.

Using two new scales, this study examined beliefs in genetic determinism and attitudes towards psychiatric genetic research in student samples from Austria, Malaysia, Romania, and the United Kingdom. For both constructs, effects of culture were detectable, whereas those related to key demographics were either small and inconsistent across samples (political orientation and religiosity) or zero (sex and age). Judged from factorial dimensionality and internal consistency, the psychometric properties of both scales were satisfactory. Belief in genetic determinism had lower prevalence and corresponded only modestly to positive attitudes towards psychiatric genetic research which had higher prevalence. The correlations of both constructs with a preference of inequality among social groups (social dominance orientation) were modest and inconsistent across samples. Both scales appear appropriate for cross-cultural applications, in particular for research into lay theories and public perceptions regarding genetic vs environmental effects on human behavior, mental disorders, and behavioral and psychiatric genetic research related to these.

Correlates of the Belief in the Inheritance of Suicide

The belief in the inheritance of suicide was not associated with manic-depressive tendencies or religiosity in a sample of 120 college students.