A test of the equal-environment assumption in twin studies of psychiatric illness

Kendler, Kenneth S.; Neale, Michael C.; Kessler, Ronald C.; Heath, Andrew C.; Eaves, Lindon J.

doi:10.1007/bf01067551

Cited by 367 publications

(253 citation statements)

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“…In addition to that, twin studies assume that MZ and DZ twins share the same common environmental experiences. This assumption can be tested by comparing phenotypic similarity in twins of perceived versus true zygosity [28,29]. The assumption is violated if the phenotypic similarity of the twins is the result of perceived zygosity rather than of true zygosity.…”

Section: Discussionmentioning

confidence: 99%

“…The assumption is violated if the phenotypic similarity of the twins is the result of perceived zygosity rather than of true zygosity. While this assumption has been tested empirically for some traits [28], this is not commonly practised as part of most twin studies. A well known bias in twin studies is a biased sample of MZ and concordant twins.…”

Section: Discussionmentioning

confidence: 99%

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Are there common genetic and environmental factors behind the endophenotypes associated with the metabolic syndrome?

et al. 2007

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Aims/hypothesis The cluster of obesity, insulin resistance, dyslipidaemia and hypertension, called the metabolic syndrome, has been suggested as a risk factor for cardiovascular disease and type 2 diabetes. The aim of the present study was to evaluate whether there are common genetic and environmental factors influencing this cluster in a general population of twin pairs. Materials and methods A multivariate genetic analysis was performed on nine endophenotypes associated with the metabolic syndrome from 625 adult twin pairs of the GEMINAKAR study of the Danish Twin Registry.Results All endophenotypes showed moderate to high heritability (0.31-0.69) and small common environmental variance (0.05-0.21). In general, genetic and phenotypic correlations between the endophenotypes were strong only within sets of physiologically similar endophenotypes, but weak to moderate for other pairs of endophenotypes. However, moderate correlations between insulin resistance indices and either obesity-related endophenotypes or triacylglycerol levels indicated that some common genetic backgrounds are shared between those components. Conclusions/interpretation We demonstrated that, in a general population, the endophenotypes associated with the metabolic syndrome apparently do not share a substantial common genetic or familial environmental background.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Are there common genetic and environmental factors behind the endophenotypes associated with the metabolic syndrome?

et al. 2007

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“…inappropriately inflating estimates of trait heritability). Such characteristics, for example, physical twin similarity (Hettema et al 1995), self-perceived zygosity (Xian et al 2000), perceived zygosity and associated parental approach to rearing their twins (Kendler et al 1993(Kendler et al , 1994Kendler & Gardner, 1998 ;Cronk et al 2002), and physical and emotional closeness between the twins (LaBuda et al 1997 ;Kendler & Gardner, 1998;Cronk et al 2002) have been shown to be uncorrelated with zygosity differences in a number of psychiatric disorders such as alcohol and illicit drug dependence, major depression, anxiety, and externalizing disorders, supporting the validity of the equal environmental assumption in twin studies assessing these disorders. The equal environment assumption has also been found to be valid for DSM-III-R nicotine dependence in female (Kendler & Gardner, 1998) and male twins (Xian et al 2000).…”

Section: Discussionmentioning

confidence: 99%

Defining nicotine dependence for genetic research: evidence from Australian twins

et al. 2004

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Background. Whether current criteria used to define nicotine dependence are informative for genetic research is an important empirical question. The authors used items of the DSM-IV and of the Heaviness of Smoking Index to characterize the nicotine dependence phenotype and to identify salient symptoms in a genetically informative community sample of Australian young adult female and male twins.Method. Phenotypic and genetic factor analyses were performed on nine dependence symptoms (the seven DSM-IV substance dependence criteria and the two Heaviness of Smoking Index (HSI) items derived from the Fagerstro¨m Tolerance Questionnaire, time to first cigarette in the morning and number of cigarettes smoked per day). Phenotypic and genetic analyses were restricted to ever smokers.Results. Phenotypic nicotine dependence symptom covariation was best captured by two factors with a similar pattern of factor loadings for women and men. In genetic factor analysis item covariation was best captured by two genetic but one shared environmental factor for both women and men ; however, item factor loadings differed by gender. All nicotine dependence symptoms were substantially heritable, except for the DSM-IV criterion of 'giving up or reducing important activities in order to smoke ', which was weakly familial.Conclusions. The salient behavioral indices of nicotine dependence are similar for women and men. DSM-IV criteria of tolerance, withdrawal, and experiencing difficulty quitting and HSI items time to first cigarette in the morning and number of cigarettes smoked per day may represent the most highly heritable symptoms of nicotine dependence for both women and men.

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“…This would artificially inflate estimates of heritability. Research investigating this issue, however, suggests that the more similar environments experienced by MZ twins are due to genetic similarities between the twins causing them to elicit or produce more similar environments (Kendler, Neale, Kessler, Heath, & Eaves, 1993). A further general limitation concerns chorionicity.…”

Section: Limitationsmentioning

confidence: 99%

Exploring the Association Between Anxiety and Conduct Problems in a Large Sample of Twins Aged 2–4

Gregory

Eley

Plomin

2004

J Abnorm Child Psychol

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Anxiety and conduct problems covary, yet studies have not explored the genetic and environmental origins of this association.We analyzed parent-reported anxiety and conduct problems in 6,783 pairs of twins at 2-, 3-, and 4-years of age. As anxiety and conduct problems were fairly stable across the three ages (average 1-year correlation was .53), ratings from all three were combined. The aggregate anxiety and conduct ratings correlated .33 for boys and .30 for girls. Bivariate genetic analyses indicated fairly low genetic correlations (.31 for boys, .16 for girls), and high shared environmental correlations (1.0 for boys and 0.99 for girls) between anxiety and conduct problems. Most of the phenotypic correlation was accounted for by shared environmental mediation (65% for boys and 94% for girls), indicating that many of the same family environmental factors are responsible for the development of both anxiety and conduct problems.Keywords: anxiety; conduct; twins; genes; environment.Goldsmiths Research Online. A twin study of anxiety and conflict. 2Anxiety and conduct problems are common areas of difficulty in child psychopathology (Anderson, Williams, McGee, & Silva, 1987). Although each may appear alone these problems also co-occur in both epidemiological and clinic-referred samples (Fergusson & Horwood, 1993;Russo & Beidel, 1994). This is interesting because at first glance the symptoms of anxiety appear to be counter indicative of conduct problems, and the presumed causes of anxiety and conduct problems would seem to imply a negative association. Although estimates as to the degree of overlap between anxiety and externalizing problems vary between studies, a reviewof the literature has reported that between 2 and 21% of children referred for anxiety had externalizing problems (Russo & Beidel, 1994). Some of the studies leading to these estimates combine child and adolescent data, and co-occurrence between anxiety and externalizing problems may be greater in preadolescent as compared to adolescent samples. For example, in a study of children diagnosed with overanxious disorder, 61% of those aged 5-11 were also diagnosed with an externalizing disorder, but only 15% of those aged 12-19 received such a diagnosis (Strauss, Lease, Last, & Francis, 1988).Over the past decade there has been interest in using genetic data to examine the origins of associations between traits (for a textbook on behavioral genetics see Plomin, DeFries, McClearn, & McGuffin, 2001). Such data can be used to estimate the extent to which associations are mediated by genes, shared environment (any environmental influence contributing to the resemblance of family members) and nonshared environment (environmental factors not contributing to the resemblance of family members). An example of genetic mediation of the association between anxiety and conduct could be via the serotonin system-which has been associated with both anxiety and conduct problems (Eley, Collier,&McGuffin, 2002;Unis et al., 1997), although as discussed later most gen...

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A test of the equal-environment assumption in twin studies of psychiatric illness

Cited by 367 publications

References 25 publications

Are there common genetic and environmental factors behind the endophenotypes associated with the metabolic syndrome?

Are there common genetic and environmental factors behind the endophenotypes associated with the metabolic syndrome?

Defining nicotine dependence for genetic research: evidence from Australian twins

Exploring the Association Between Anxiety and Conduct Problems in a Large Sample of Twins Aged 2–4

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