Beyond Heritability

The heritability of human behavioral traits is now well established, due in large measure to classical twin studies. We see little need for further studies of the heritability of individual traits in behavioral science, but the twin study is far from having outlived its usefulness. The existence of pervasive familial influences on behavior means that selection bias is always a concern in any study of the causal effects of environmental circumstances. Twin samples continue to provide new opportunities to identify causal effects with appropriate genetic and shared environmental controls. We discuss environmental studies of discordant twin pairs and twin studies of genetic and environmental transactions in this context.

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An Epidemiologic, Longitudinal, and Discordant-Twin Study of the Association Between Gambling Disorder and Suicidal Behaviors

Clinical Psychological Science ◽

10.1177/21677026211062599 ◽

2022 ◽

pp. 216770262110625

Author(s):

Wendy S. Slutske ◽

Christal N. Davis ◽

Michael T. Lynskey ◽

Andrew C. Heath ◽

Nicholas G. Martin

Keyword(s):

Suicide Attempt ◽

Twin Study ◽

Financial Crises ◽

Gambling Disorder ◽

Twin Studies ◽

Genetic Influences ◽

Disordered Gambling ◽

Suicidal Behaviors ◽

Men And Women ◽

Discordant Twin

Gambling disorder is associated with suicidal behaviors, but it is not clear whether the association is due to common etiologic factors or to gambling disorder being causally related to suicidality. This question was examined from the perspective of epidemiologic, longitudinal, and discordant-twin studies. The results suggested that the causes of the association with disordered gambling differed for suicidal ideation, plan, and attempt and differed for men and women. The association of suicidal thoughts with disordered gambling was noncausally explained by common genetic influences among women but not men. Conversely, there was evidence consistent with a potentially causal influence of disordered gambling on suicide attempt among men but not women, which might have been related to gambling-related financial problems. The use of monetary data to identify individuals experiencing financial harms associated with their gambling may represent a more practicable target for screening, intervention, and prevention and may reduce gambling-related financial crises, thereby warding off a potential gambling-related suicide attempt.

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The Value of Twins for Health and Medical Research: A Third of a Century of Progress

Twin Research and Human Genetics ◽

10.1017/thg.2020.4 ◽

2020 ◽

Vol 23 (1) ◽

pp. 8-15 ◽

Cited By ~ 2

Author(s):

Jeffrey M. Craig ◽

Lucas Calais-Ferreira ◽

Mark P. Umstad ◽

Dedra Buchwald

Keyword(s):

Genetic Variation ◽

Medical Research ◽

Twin Study ◽

Environmental Influences ◽

Twin Studies ◽

Twin Research ◽

Study Designs ◽

Genetic Contributions

AbstractIn 1984, Hrubec and Robinette published what was arguably the first review of the role of twins in medical research. The authors acknowledged a growing distinction between two categories of twin studies: those aimed at assessing genetic contributions to disease and those aimed at assessing environmental contributions while controlling for genetic variation. They concluded with a brief section on recently founded twin registries that had begun to provide unprecedented access to twins for medical research. Here we offer an overview of the twin research that, in our estimation, best represents the field has progress since 1984. We start by summarizing what we know about twinning. We then focus on the value of twin study designs to differentiate between genetic and environmental influences on health and on emerging applications of twins in multiple areas of medical research. We finish by describing how twin registries and networks are accelerating twin research worldwide.

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A Registry of Adult African American Twins: The Carolina African American Twin Study of Aging

Twin Research and Human Genetics ◽

10.1017/thg.2012.79 ◽

2012 ◽

Vol 16 (1) ◽

pp. 476-480 ◽

Cited By ~ 8

Author(s):

Keith E. Whitfield

Keyword(s):

Mental Health ◽

North Carolina ◽

African American ◽

Twin Study ◽

Twin Studies ◽

Forced Expiratory Volume ◽

Major Objective ◽

Twin Design ◽

Public Records ◽

Birth Records

Twin studies have seldom addressed ethnicity as one of the possible factors that create unique combinations of genetic and environmental influences. The major objective of the Carolina African American Twin Study of Aging is to identify the proportion of the genetic and environmental sources of individual variation in measures of health and behavioral factors in a sample of adult African Americans. Drawn from birth records from the State of North Carolina, this in-person study used public records to identify a cohort of twins between 22 and 92 years of age (X = 49.82 yrs, SD = 14.62), 39.7% of which were men. Members of non-intact twin pairs and siblings were also recruited to explore alternative models to the classic twin design. To date, the project has contributed to knowledge about blood pressure, forced expiratory volume, chronic illness, body mass index, and waist-hip ratio memory, personality, social, and demographic factors, mortality, and mental health.

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The Concordance and Heritability of Type 2 Diabetes in 34,166 Twin Pairs From International Twin Registers: The Discordant Twin (DISCOTWIN) Consortium

Twin Research and Human Genetics ◽

10.1017/thg.2015.83 ◽

2015 ◽

Vol 18 (6) ◽

pp. 762-771 ◽

Cited By ~ 59

Author(s):

Gonneke Willemsen ◽

Kirsten J. Ward ◽

Christopher G. Bell ◽

Kaare Christensen ◽

Jocelyn Bowden ◽

...

Keyword(s):

Type 2 Diabetes ◽

Medical Records ◽

Fasting Glucose ◽

Meta Analysis ◽

Twin Studies ◽

Same Sex ◽

The United Kingdom ◽

High Heritability ◽

Discordant Twin

Twin pairs discordant for disease may help elucidate the epigenetic mechanisms and causal environmental factors in disease development and progression. To obtain the numbers of pairs, especially monozygotic (MZ) twin pairs, necessary for in-depth studies while also allowing for replication, twin studies worldwide need to pool their resources. The Discordant Twin (DISCOTWIN) consortium was established for this goal. Here, we describe the DISCOTWIN Consortium and present an analysis of type 2 diabetes (T2D) data in nearly 35,000 twin pairs. Seven twin cohorts from Europe (Denmark, Finland, Norway, the Netherlands, Spain, Sweden, and the United Kingdom) and one from Australia investigated the rate of discordance for T2D in same-sex twin pairs aged 45 years and older. Data were available for 34,166 same-sex twin pairs, of which 13,970 were MZ, with T2D diagnosis based on self-reported diagnosis and medication use, fasting glucose and insulin measures, or medical records. The prevalence of T2D ranged from 2.6% to 12.3% across the cohorts depending on age, body mass index (BMI), and national diabetes prevalence. T2D discordance rate was lower for MZ (5.1%, range 2.9–11.2%) than for same-sex dizygotic (DZ) (8.0%, range 4.9–13.5%) pairs. Across DISCOTWIN, 720 discordant MZ pairs were identified. Except for the oldest of the Danish cohorts (mean age 79), heritability estimates based on contingency tables were moderate to high (0.47–0.77). From a meta-analysis of all data, the heritability was estimated at 72% (95% confidence interval 61–78%). This study demonstrated high T2D prevalence and high heritability for T2D liability across twin cohorts. Therefore, the number of discordant MZ pairs for T2D is limited. By combining national resources, the DISCOTWIN Consortium maximizes the number of discordant MZ pairs needed for in-depth genotyping, multi-omics, and phenotyping studies, which may provide unique insights into the pathways linking genes to the development of many diseases.

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Genetic influences on suicide and nonfatal suicidal behavior: Twin study findings

European Psychiatry ◽

10.1016/j.eurpsy.2009.12.008 ◽

2010 ◽

Vol 25 (5) ◽

pp. 264-267 ◽

Cited By ~ 46

Author(s):

N.L. Pedersen ◽

A. Fiske

Keyword(s):

Suicidal Behavior ◽

Suicide Attempts ◽

Case Series ◽

Twin Studies ◽

Population Based ◽

Genetic Influences ◽

Familial Influences ◽

Age And Gender Differences ◽

And Gender ◽

Future Work

AbstractIt has been well established that suicidal behavior is familial. Twin studies provide a unique opportunity to distinguish genetic effects from other familial influences. Consistent with findings from previous twin studies, including case series and selected samples, data from the population-based Swedish Twin Registry clearly demonstrate the importance of genetic influences on suicide. Twin studies of suicidal ideation and suicide attempts also implicate genetic influences, even when accounting for the effects of psychopathology. Future work is needed to evaluate the possibility of age and gender differences in heritability of suicide and nonfatal suicidal behavior.

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Protocol for a longitudinal twin birth cohort study to unravel the complex interplay between early-life environmental and genetic risk factors in health and disease: the Chongqing Longitudinal Twin Study (LoTiS)

BMJ Open ◽

10.1136/bmjopen-2017-017889 ◽

2018 ◽

Vol 8 (2) ◽

pp. e017889 ◽

Cited By ~ 4

Author(s):

Chao Tong ◽

Li Wen ◽

Yinyin Xia ◽

Pamela Leong ◽

Lan Wang ◽

...

Keyword(s):

Genetic Variation ◽

Twin Study ◽

Twin Studies ◽

Birth Cohort Study ◽

Clinical Trial Registry ◽

Time Points ◽

Intermediate Phenotypes ◽

Genes And Environment ◽

Depth Analysis ◽

Longitudinal Twin Study

IntroductionNon-communicable diseases (NCD) now represent the major burden of adverse health in most countries. It is clear that much of the risk of such conditions begins very early in life, potentially in utero. Given their complex aetiology, an understanding of the origins of NCD requires an in-depth analysis of the interplay between genetic variation and environment, preferably over time. For decades, twin studies have played a key role in understanding such traits. Their strength lies in the ability to disentangle genetic and environmental factors that contribute to a phenotype. This is done by comparing genetically identical monozygotic (MZ) with dizygotic twins, who share on average 50% of genetic variation, or by comparing MZ twins within a pair. This study aims to determine the relative contributions of genes and environment to early-onset intermediate phenotypes related to later adult onset disease (such as growth and neurodevelopment) and to identify specific biomarkers and time points for emergence of phenotypes from infancy, largely independent of underlying genetic factors.Methods/designThe Chongqing Longitudinal Twin Study (LoTiS) will recruit 300 women pregnant with twins, enriched for MZ pregnancies, with follow-up to 3 years of age. Data collection will be undertaken at key time points in gestation (×3), at delivery and postnatally (×9). Maternal and infant biospecimens including blood, urine, hair, nails and buccal swabs along with measures such as fetal scans and body measurements will be collected. Additional information from questionnaires and medical records includes pregnancy, diet, sociodemographics, maternal stress, and infant growth and neurodevelopment.Ethics and disseminationThis study has been approved by the Ethics Committee of Chongqing Medical University (record no: 201530) and has been registered with the Chinese Clinical Trial Registry (registry no: ChiCTR-OOC-16008203). Results of the recruitment and all subsequent analyses will be submitted for publication in peer-reviewed journals.Trial registration numberChiCTR-OOC-16008203; Results.

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A Twin Study of Cigarette and Snus Initiation and Quantity of Use in Norwegian Adult Twins

Twin Research and Human Genetics ◽

10.1017/thg.2019.9 ◽

2019 ◽

Vol 22 (2) ◽

pp. 108-113

Author(s):

Kenneth S. Kendler ◽

Steven H. Aggen ◽

Nathan Gillespie ◽

Nikolai Czajkowski ◽

Eivind Ystrom ◽

...

Keyword(s):

Public Health ◽

Twin Study ◽

Twin Studies ◽

Self Report ◽

Shared Environment ◽

Cigarette Use ◽

Environmental Correlations ◽

Twin Models ◽

Adult Twins

AbstractWhile snus has been the focus of increasing public health interest, twin studies have examined neither sources of individual variation for its use nor the sources of resemblance between snus and cigarette use. Twins from the Norwegian Institute of Public Health Panel were assessed by self-report questionnaire for the initiation of regular use and maximal quantity used for snus and cigarettes. Twin modeling was performed using OpenMx on data from 2767 twins including 856 complete pairs. Fitting univariate twin models produced similar results for cigarette initiation and quantity with estimates of additive genetic, shared environmental and unique environmental effects of approximately 77%, 0% and 23%, respectively. Estimates of snus initiation and quantity were, respectively, approximately 53%, 26% and 21%. Joint analyses suggested that the genetic, shared environmental and unique environmental correlations between cigarette and snus initiation and quantity were +.82, 0 and +.42, respectively. However, these results could not be statistically distinguished from a model which postulated that resemblance between cigarette initiation and quantity resulted from genetic and unique environmental correlations of +.47 and +.43. Compared with cigarette initiation and quantity of use in Norwegian twins, the role of genes was less prominent and shared environment more prominent for initiation and quantity of use of snus. Joint analyses of both tobacco phenotypes suggested, but did not confirm definitively, that genetic risk factors for cigarette and snus use were similar but not identical, while shared environmental factors existed that were specific to snus use.

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Concurrent Schizophrenia-Like Psychosis in Monozygous Twins Suffering from CNS Disorder

The British Journal of Psychiatry ◽

10.1192/bjp.122.6.675 ◽

1973 ◽

Vol 122 (571) ◽

pp. 675-677 ◽

Cited By ~ 3

Author(s):

Albert West

Keyword(s):

Twin Study ◽

Genetic Factor ◽

Environmental Influences ◽

Twin Studies ◽

Identical Twin ◽

Cerebral Dysfunction ◽

The Relationship ◽

Monozygous Twins

Twin studies and investigations into the relationship between schizophrenia-like psychosis and cerebral dysfunction are of considerable interest. Refinement in twin studies has led to less emphasis being placed upon the genetic factor, but the pitfalls surrounding twin techniques, especially with regard to monozygous pairs and the similarity of their environment, have led Penrose (1971) to the opinion that twin study ‘is especially useful, not for genetical researches but in assessing the effects of environmental influences which lead to discordance in identical twin pairs'.

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Twin Studies of Political Behavior: Untenable Assumptions?

Perspectives on Politics ◽

10.1017/s1537592708081917 ◽

2008 ◽

Vol 6 (4) ◽

pp. 785-791 ◽

Cited By ~ 45

Author(s):

Jon Beckwith ◽

Corey A. Morris

Keyword(s):

Molecular Genetic ◽

Genetic Research ◽

Twin Studies ◽

First Century ◽

Behavioral Traits ◽

Political Ideologies ◽

Equal Environments Assumption ◽

Twin Method ◽

Genetic Techniques ◽

Equal Environments

Using the “classical twin method,” political scientists John Alford, Carolyn Funk, and John Hibbing conclude that political ideologies are significantly influenced by genetics, an assertion that has garnered considerable media attention. Researchers have long used human twins in attempts to assess the degree of genetic influence on various behavioral traits. Today, this methodology has been largely replaced in favor of contemporary molecular genetic techniques, and thus heritability studies have seen a diminishing role in behavioral genetic research of the twenty-first century. One important reason the twin method has been superseded is that it depends upon several questionable assumptions, the most significant of which is known as the equal environments assumption. Alford, Funk, and Hibbing argue that this crucial assumption, and thus their conclusion, holds up under empirical scrutiny. They point to several studies in support of this assumption. Here, we review the evidence presented and conclude that these attempts to test the equal environments assumption are weak, suffering significant methodological and inherent design flaws. Furthermore, much of the empirical evidence provided by these studies actually argues that, contrary to the interpretation, trait-relevant equal environments assumptions have been violated. We conclude that the equal environments assumption remains untenable, and as such, twin studies are an insufficient method for drawing meaningful conclusions regarding complex human behavior.

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