Domain-Specific and Domain-General Genetic and Environmental Effects on the Intensity of Visual Aesthetic Appraisal

Visual aesthetic experiences are universally shared and uniquely diversified components of every human culture. The contribution of genetic and environmental factors to variation in aesthetic appraisal has rarely been examined. Here, we analysed variation in the intensity of aesthetic appraisal in 558 monozygotic and 216 dizygotic same sex adult twin pairs when they were presented with three kinds of visual stimuli: abstract objects, sceneries, and faces. We estimated twin resemblance and heritability for the three stimuli types, as well as a shared genetic factor between the three stimuli types. Genetic factors played a moderate role in the variation of intensity of aesthetic appraisal (heritability 26 to 41%). Both shared and unique underlying genetic factors significantly accounted for domain-general and domain-specific differences. Our findings are the first to show the extent to which variation in the intensity of aesthetic experiences result from the contribution of genetic and environmental factors.

Social Comparison Orientation in Monozygotic and Dizygotic Twins

Twin research has offered evidence that monozygotic (MZ) twins are more socially close than dizygotic (DZ) twins, but has not paid much attention to the way twins compare themselves with their co-twin. The few studies in this area suggest that ‘horizontal comparisons’ (social comparison motivated by solidarity or communion with others) matter more for MZ twins than for DZ twins, at least when the co-twin is the social comparison standard. Consistent with this view, we predicted higher interest in MZ twins relative to DZ twins to select their co-twin rather than other people in general as the social comparison standard. The Social Comparison Orientation (SCO) scale, which measures the inclination to compare with others in a horizontal rather than vertical mode (comparing either upward or downward), was administered in 90 MZ pairs and 57 same-sex DZ pairs (63% female; average age 18.06 years) from the Netherlands Twin Register. MZ twin pairs showed significantly higher SCO scores than DZ twin pairs (with a large effect size) on the co-twin SCO, whereas the two groups did not differ from each other on the general SCO excluding the co-twin as social comparison standard. In MZ twin pairs, anxiety was associated with social comparison with others in general, not with their co-twin. For both scales, twin resemblance was explained by additive genetic variance. The present findings provide direct evidence that horizontal comparisons with the co-twin are of particular importance for MZ twins.

A Genetic Analysis of Coffee Consumption in a Sample of Dutch Twins

Caffeine is by far the most commonly used psychoactive substance. Caffeine is consumed regularly as an ingredient of coffee. Coffee consumption and coffee preference was explored in a sample of 4,495 twins (including 1,231 pairs) registered with the Netherlands Twin Registry. Twin resemblance was assessed by tetrachoric correlations and the influence of both genetic and environmental factors was explored with model fitting analysis in MX. Results showed moderate genetic influences (39%) on coffee consumption. The remaining variance was explained by shared environmental factors (21%) and unique environmental factors (40%). The variance in coffee preference (defined as the proportion of coffee consumption relative to the consumption of coffee and tea in total) was explained by genetic factors (62%) and unique environmental factors (38%).

The Differential Heritability of Regular Tobacco Use Based on Method of Administration

Several large studies have demonstrated that the liability to smoke cigarettes is strongly genetically influenced. However, the role of genetic and environmental risk factors in the use of other common forms of tobacco use has yet to be studied. Data on the regular use of cigarettes, cigars, pipes, dip (moist snuff), and chewing tobacco from 2634 male twins were analyzed with ACE structural equation models. Twin similarity for regular cigarette and dip use was largely genetic in origin. However, twin resemblance for chewing tobacco was just about equally the result of genes and shared environment, and twin similarity for use of pipes and cigars was entirely the result of shared environmental factors. Thus, the genetic influences on the liability for regular tobacco use appear to vary based on tobacco type. The causes for the use of different forms of tobacco are complex and worthy of further study.

Parent–Child Feedback Predicts Sibling Contrast: Using Twin Studies to Test Theories of Parent–Offspring Interaction in Infant Behavior

Several studies report apparent sibling contrast effects in analyses of twin resemblance. In the presence of genetic differences, contrast effects reduce the dizygotic (DZ) twin correlation relative to that in monozygotic (MZ) twins and produce higher DZ than MZ variance. Explanations of contrast effects are typically cast in terms of direct social interaction between twins or an artifact of the process of rating children by their parents. We outline a model for sibling imitation and contrast effects that depends on social interaction between parents and children. In addition to predicting the observed pattern of twin variances and covariances, the parental mediation of child imitation and contrast effects leads to differences in the variance of parents of MZ and DZ twins and differences between the correlations of parents with their MZ and DZ children.

Sex differences in genetic and environmental risk factors for irrational fears and phobias

Background. For irrational fears and their associated phobias, epidemiological studies suggest sex differences in prevalence and twin studies report significant genetic effects. How does sex impact on the familial transmission of liability to fears and phobias?Methods. In personal interviews with over 3000 complete pairs (of whom 1058 were opposite-sex dizygotic pairs), ascertained from a population-based registry, we assessed the lifetime prevalence of five phobias and their associated irrational fears analysed using a multiple threshold model. Twin resemblance was assessed by polychoric correlations and biometrical model-fitting incorporating sex-specific effects.Results. For agoraphobia, situational and blood/injury fear/phobia, the best fit model suggested equal heritability in males and females and genetic correlations between the sexes of less than +0·50. For animal fear/phobias by contrast, the best fit model suggested equal heritability in males and females and a genetic correlation of unity. No evidence was found for an impact of family environment on liability to these fears or phobias. For social phobias, twin resemblance in males was explained by genetic factors and in females by familial–environmental factors.Conclusion. The impact of sex on genetic risk may differ meaningfully across phobia subtypes. Sex-specific genetic risk factors may exist for agoraphobia, social, situational and blood-injury phobias but not for animal fear/phobia. These results should be interpreted in the context of the limited power of twin studies, even with large sample sizes, to resolve sex-specific genetic effects.

Panic syndromes in a population-based sample of male and female twins

Background. The risk for panic disorder (PD) is substantially increased in relatives of probands with PD. Prior literature provides only limited information about the degree to which this increase is due to genetic factors or family environment.Methods. In personal interviews with both members of 3194 twin pairs, we assessed the lifetime history of lifetime panic attacks and PD. Twin resemblance was assessed by tetrachoric correlation and single and multiple threshold biometrical model fitting.Results. As fully syndromal PD, by DSM-III-R criteria, was too rare to analyse usefully we examined four other dichotomous definitions of increasing stringency: panic probe and very broad, broad and intermediate PD. For all four definitions and for the multiple threshold analyses, the best-fit model indicated that twin resemblance was due solely to genetic factors with a moderate heritability (33–43%). For the broad and intermediate dichotomous definitions of PD, however, a model with twin resemblance due to familial–environmental factors fit nearly as well. No gender effects were seen on the genetic risk factors for these PD-like syndromes.Conclusion. Even with large epidemiological samples of twins, studying disorders as uncommon as PD is problematical. Despite these difficulties, our results suggest that: (i) narrowly and broadly defined PD are probably on the same continuum of liability; (ii) twin resemblance for these PD-like syndromes is likely due largely to genetic factors with a moderate level of heritability although a contribution of familial–environmental factors cannot be excluded; and, (iii) the same familial risk factors impact, to a similar degree, on the liability to PD in males and females.

Cocaine use, abuse and dependence in a population-based sample of female twins

BackgroundAlthough cocaine use in women has increased substantially over the past half-century, we understand little about the aetiology in women of cocaine use and abuse, and know almost nothing about the role of genetic factors.MethodWe obtained by telephone interview a history of lifetime cocaine use, abuse and dependence from 1934 individual twins from female–female pairs ascertained through a population-based registry, including both members of 485 monozygotic (MZ) and 335 dizygotic (DZ) pairs.ResultsThe prevalence of lifetime cocaine use, abuse and dependence were 14.0%, 3.3% and 2.3%. Probandwise concordance rates, in MZ and DZ twins, respectively, were: cocaine use 54% and 42%; cocaine abuse 47% and 8% and cocaine dependence 35% and 0%. In MZ and DZ twins, odds ratios were: cocaine use 14.2 and 6.7 and cocaine abuse 40.8 and 2.7. Biometrical model-fitting suggested that twin resemblance for liability to cocaine use was due to both genetic and familial–environmental factors while twin resemblance for cocaine abuse and symptoms of dependence was due solely to genetic factors. Estimated heritabilities were: cocaine use 0.39, cocaine abuse 0.79 and symptoms of dependence 0.65.ConclusionsThe vulnerability to cocaine use and particularly cocaine abuse and dependence in women is substantially influenced by genetic factors.