Shared Environmental Influences Research Articles

The Association Between Toddlerhood Self-Control and Later Externalizing Problems.

Lower self-control is a significant correlate or predictor of a wide range of adult outcomes, and this association may be due to more general tendencies toward childhood externalizing problems. The present study examined the association between toddlerhood self-control expressed within a "don't" compliance task (at 14-36months) and later externalizing problems (parent-reported externalizing problems from age 4 to 12 years, teacher-reported externalizing problems from age 7 to 12 years, and self-reported conduct disorder symptoms at age 17years) in a longitudinal, genetically informative study. The slope of self-control, but not its intercept, predicted later teacher-reported, but not parent- or self-reported, externalizing problems. That is, increase in self-control during toddlerhood was associated with lower levels of later teacher-reported externalizing problems. The slope of self-control was no longer a significant predictor of teacher-reported externalizing problems after controlling for observed disregard for others, a robust predictor of externalizing problems. Thus, the hypothesis that self-control is the primary predictor of externalizing problems was not supported. Results from genetic analyses suggested that the covariance between the slope of self-control and teacher-reported externalizing problems is due to both genetic and shared environmental influences.

Genetic and environmental architecture of executive functions in midlife.

Research on executive functions (EFs) has revealed evidence for general abilities that underlie performance across multiple EF tasks and domains. This Common EF factor is highly stable in adolescence through young adulthood, correlates with other important cognitive abilities, and is explained largely by genetic influences. However, little is known about Common EF beyond young adulthood. This study examines 3 hypotheses regarding the latent structure, genetic/environmental etiology, and cognitive correlates of Common EF in middle age. We examined data from 1,284 middle-aged twins (51-60 years) in the Vietnam Era Twin Study of Aging who completed 7 neuropsychological measures of EFs, as well as measures of general cognitive ability and processing speed. Our confirmatory factor analysis indicated that Common EF explained variation across all 7 EF tasks. Inhibition and shifting were subsumed entirely under the Common EF factor, and there was an additional working memory span-specific factor. Common EF was heritable in midlife (a2 = .46), with additional evidence for both shared environmental influences (c2 = .41) and nonshared environmental influences (e2 = .13). Higher Common EF was moderately associated with higher general cognitive ability, measured both in early adulthood and midlife, and faster processing speed in midlife. These correlations were primarily driven by shared genetic influences. These results support the hypothesis that Common EF captures similar EF abilities in midlife as in adolescence and young adulthood. However, environmental influences may explain a larger portion of variance in this construct as individuals age. (PsycINFO Database Record

Examination of Cross-Sectional Associations of Neighborhood Deprivation and Alcohol Outlet Density With Hazardous Drinking Using a Twin Design.

The purpose of this study was to examine whether neighborhood socioeconomic deprivation and alcohol outlet density are associated with hazardous drinking using a co-twin design to control for confounding because of genetic and shared environmental factors. The study sample included cross-sectional data from 1,996 same-sex adult twin pairs (mean age = 36.6; 65.9% female) from the Washington State Twin Registry. The Singh Index was used to characterize neighborhood social deprivation for participants' census tract of residence. Geocoded alcohol outlet data were used to create a measure of census tract alcohol outlet density. The three-item Alcohol Use Disorders Identification Test-Consumption scale (AUDIT-C) was used to measure the level of hazardous drinking. Poisson mixed-effects models were used to examine associations between neighborhood factors and AUDIT-C score. Covariates included household income, level of education completed, non-White race, sex, and rurality of residence. Accounting for covariates, there was a statistically significant within-pair association between neighborhood socioeconomic deprivation and a higher level of hazardous drinking. There was no within-pair association between the density of alcohol outlets and hazardous drinking. Associations did not differ by zygosity. The socioeconomic conditions of the neighborhood may play an important role in the development of alcohol misuse even after accounting for genetic and shared environmental influences. Twin designs may be a promising complementary approach to investigating the role of neighborhood characteristics on alcohol and substance use. Further research is needed to better understand the ways through which and for whom neighborhood characteristics may influence hazardous drinking.

Familial aggregation of tonsillectomy in early childhood and adolescence.

BackgroundThe tonsils are immunological gatekeepers against pathogens. Immunological response to tonsillitis may vary clinically from no enlargement of the tonsils to nearly obstructive conditions. In this investigation, we studied the familial aggregation of tonsillectomy, as an indicator of the extent to which tonsillar immune responses to infections might be genetically controlled.MethodsData on kinship relations and vital status from the Danish Civil Registration System were used to establish a cohort of Danes with relatives born since 1977. Tonsillectomies in all hospitals and clinics from 1977 to 2013 were identified in national registers together with the indication for tonsillectomy. Rate ratios (RRs) for tonsillectomy >1 year after tonsillectomy in specific types of relatives (first to fourth degree) were estimated in Poisson regression models with adjustment for calendar period, sex, age, and total number of specified relatives.ResultsA cohort of 2.4 million persons was followed for 44,100,697 million person-years (mean 18.4 years/person), and included 148,190 tonsillectomies. RRs of tonsillectomy were consistently higher when the relatedness and the number of tonsillectomized relatives were higher. RRs were similar in boys and girls, but were larger in early childhood. Additional analyses suggested that this relatively higher RR at younger ages was due to a larger influence of shared environment at younger ages, whereas the genetic influence was similar at all ages. Results were similar for tonsillectomies performed strictly due to tonsillitis.ConclusionsGenetic factors appear to predispose to severe tonsillitis underlying tonsillectomies, regardless of age and sex. Further studies are needed to understand how genes regulate the tonsils’ immune response against infections.

Differential environmental influences on the development of cognitive abilities during childhood

Twin studies have shown strong evidence that cognitive abilities are heritable. This longitudinal study examines genetic and environmental influences on distinct developmental patterns of verbal and non-verbal cognitive abilities from age 7 to 12 in 4718 British twins. Six subgroups with distinct patterns were identified with comparable heritabilities of group membership (ranging 0.37–0.62). Non-shared environmental influences that differentiate family members on group membership appear to be particularly strong in the three subgroups that demonstrated substantial developmental mean changes of cognitive abilities (ranging 0.51–0.54), compared to the other three subgroups with relatively stable mean levels (ranging 0.29–0.34). Shared environmental influences making family members similar for group membership were significant in only two subgroups – among the children with continuously low scores (0.20) and developmental early starters (0.28). These results suggest the existence of distinct developmental patterns of cognitive abilities. The impact of shared and non-shared environment on the membership of different developmental patterns may be greater for some children than others.

Home environmental influences on children's language and reading skills in a genetically sensitive design: Are socioeconomic status and home literacy environment environmental mediators and moderators?

This twin study examined how family socioeconomic status (SES) and home literacy environment (HLE) contributes to Chinese language and reading skills. It included 312 Chinese twin pairs aged 3 to 11. Children were individually administered tasks of Chinese word reading, receptive vocabulary and reading-related cognitive skills, and nonverbal reasoning ability. Information on home environment was collected through parent-reported questionnaires. Results showed that SES and HLE mediated shared environmental influences but did not moderate genetic influences on general language and reading abilities. Also, SES and HLE mediated shared environmental contributions to receptive vocabulary and syllable and rhyme awareness, but not orthographic skills. The findings of this study add to past twin studies that focused on alphabetic languages, suggesting that these links could be universal across languages. They also extend existing findings on SES and HLE's contributions to reading-related cognitive skills.

Are there individual and sibling differences in appraisals of interparental conflict?

Despite decades of empirical literature documenting the harmful effects of frequent, intense, violent, and unresolved interparental conflict on children's adjustment, there is considerable variability in the extent to which marital conflict contributes to the development of children's emotional and behavioral problems. Past research has documented links between properties of interparental conflict itself (e.g., intensity, frequency), children's appraisals of conflict, and children's outcomes, yet less is known about the role of individual and family characteristics in predicting children's conflict appraisals. Sibling studies may be especially helpful in understanding these individual differences yet are notably lacking in marital conflict research. The current study examines individual- and family-characteristic predictors of adolescents' appraisals of conflict in a study of 153 adolescents as well as sibling similarities in conflict appraisals in a subsample of 50 pairs of siblings. Controlling for parent reports of the frequency, intensity, and resolution of interparental conflict, parent-child relationship quality and stressful life events predicted conflict appraisals. In addition, there was nonindependence of sibling appraisals of conflict properties, but self-blame and threat appraisals appeared independent across siblings. Greater discrepancies in siblings' conflict appraisals were related to more negative marital conflict and discrepancies in parent-child relationship quality, and were found in mixed-sex sibling dyads. Implications for future studies on factors that impact children's appraisals of conflict and in particular making use of sibling studies to examine shared environmental and individual influences on appraisals is highlighted. (PsycINFO Database Record

A twin study of genetic and environmental influences on relationship between attention deficit and anxiety/depression in children and adolescents

Objective: To understand the genetic and environmental influences on the relationship between attention deficit and anxiety/depression in children and adolescents. Methods: A total of 1 062 same-sex twins aged 6-18 years were included in this study. A parent-rated child behavior checklist (CBCL) was used in the assessment. Software Mx was used to fit the univariate model of structural equation. The relationship between attention deficit and anxiety/depression was analyzed through bivariate genetic modeling. Results: The genetic factor had influence on the relationship between attention deficit and anxiety/depression (r(g)=0.48). Shared and non-shared environmental correlation scores of attention deficit and anxiety/depression were 0.86 and 0.14 respectively. Conclusion: Common genetic and shared environmental influences can explain the relationship between attention deficit and anxiety/depression in children and adolescents.

Symptoms of Depression and Risk of Low Back Pain: A Prospective Co-Twin Study.

To investigate whether symptoms of depression increase the risk of low back pain (LBP), after adjusting for genetic and environmental influences. Baseline data of 1607 twins from the Murcia Twin Registry (Spain) were collected in 2009 to 2011 and follow-up data in 2013. Twins answered questions on depression-related symptomatology and LBP. Only participants not reporting chronic LBP (pain >6 mo) at baseline were included. The association between symptoms of depression and LBP was investigated using logistic regression analysis including the complete sample. Subsequent matched within-pair case-control analyses were performed with all complete dizygotic twin pairs discordant for LBP, followed by monozygotic twins. In the total sample analysis, symptoms of depression did not significantly increase the risk of chronic LBP (odds ratio [OR]=1.40; 95% confidence interval [CI], 0.96-2.03), LBP care seeking (OR=1.21; 95% CI, 0.81-1.81), or activity-limiting LBP (OR=1.09; 95% CI, 0.69-1.72). State depression (participants' symptoms at the moment of the interview) was significantly associated with future care seeking (OR=1.06; 95% CI, 1.01-1.12) and activity-limiting LBP (OR=1.07; 95% CI, 1.01-1.14). A significant association was found between trait depression and activity-limiting LBP (OR=1.05; 95% CI, 1.01-1.10), but not for the other LBP outcomes. No significant association was observed in any of the subsequent case-control analyses. The magnitude of the association between depression and LBP seems to be small and may be confounded by genetic and early shared environment influences, although firm conclusions could not be made due to small sample size in the case-control analysis. In addition, the observed association is dependent on the method of assessment used for both conditions.

Emotional over- and under-eating in early childhood are learned not inherited

Emotional overeating (EOE) has been associated with increased obesity risk, while emotional undereating (EUE) may be protective. Interestingly, EOE and EUE tend to correlate positively, but it is unclear whether they reflect different aspects of the same underlying trait, or are distinct behaviours with different aetiologies. Data were from 2054 five-year-old children from the Gemini twin birth cohort, including parental ratings of child EOE and EUE using the Child Eating Behaviour Questionnaire. Genetic and environmental influences on variation and covariation in EUE and EOE were established using a bivariate Twin Model. Variation in both behaviours was largely explained by aspects of the environment completely shared by twin pairs (EOE: C = 90%, 95% CI: 89%-92%; EUE: C = 91%, 95% CI: 90%-92%). Genetic influence was low (EOE: A = 7%, 95% CI: 6%-9%; EUE: A = 7%, 95% CI: 6%-9%). EOE and EUE correlated positively (r = 0.43, p < 0.001), and this association was explained by common shared environmental influences (BivC = 45%, 95% CI: 40%-50%). Many of the shared environmental influences underlying EUE and EOE were the same (rC = 0.50, 95% CI: 0.44, 0.55). Childhood EOE and EUE are etiologically distinct. The tendency to eat more or less in response to emotion is learned rather than inherited.

Little Evidence That Socioeconomic Status Modifies Heritability of Literacy and Numeracy in Australia.

Socioeconomic status (SES) has been found to moderate the influence of genes and the environment on cognitive ability, such that genetic influence is greater when SES is higher, and the shared environment is greater when SES is lower, but not in all Western countries. The effects of both family and school SES on the heritability of literacy and numeracy in Australian twins aged 8, 10, 12, and 14years with 1,307, 1,235, 1,076, and 930 pairs at each age, respectively, were tested. Shared environmental influences on Grade 3 literacy were greater with low family SES, and no other moderating effects of SES were significant. These findings are contrasted with results from the United States and the United Kingdom.

Genetic and environmental influences on emotion regulation: A twin study of cognitive reappraisal and expressive suppression.

Previous studies have established that personality traits related to emotionality are moderately heritable. However, the relative heritability of the strategies people use to regulate emotions is unknown. The present study compared the magnitude of additive genetic, shared environmental, and nonshared environmental influences on 2 commonly used emotion regulation strategies: cognitive reappraisal and expressive suppression. In 743 twin pairs (1,486 twins), we replicated previous estimates of heritability of neuroticism (a2 = .41). Furthermore, cognitive reappraisal was significantly less heritable and more influenced by nonshared environment (a2 = .20; e2 = .80) than either neuroticism or suppression (a2 = .35; e2 = .65), another emotion regulation strategy. Finally, Cholesky decomposition modeling suggested that while there were common genetic and environmental influences on neuroticism, reappraisal and suppression, there were also significant nonshared environmental influences common between reappraisal and adaptive emotional functioning after controlling for neuroticism and suppression. These findings highlight that different aspects of emotional processing, even the use of different emotion regulation strategies, are differentially heritable. The importance of the nonshared environmental influences specific to reappraisal and adaptive emotional functioning speaks to the potential impact of social context, social partners, and psychosocial interventions on reappraisal habits. (PsycINFO Database Record

Pathways of Intergenerational Transmission of Advantages during Adolescence: Social Background, Cognitive Ability, and Educational Attainment

Educational attainment in adolescence is of paramount importance for attaining higher education and for shaping subsequent life chances. Sociological accounts focus on the role of differences in socioeconomic resources in intergenerational reproduction of educational inequalities. These often disregard the intergenerational transmission of cognitive ability and the importance of children's cognitive ability to educational attainment. Psychological perspectives stress the importance of cognitive ability for educational attainment but underemphasize potentially different roles of specific socioeconomic resources in shaping educational outcomes, as well as individual differences in cognitive ability. By integrating two strands of research, a clearer picture of the pathways linking the family of origin, cognitive ability, and early educational outcomes can be reached. Using the population-based TwinLife study in Germany, we investigated multidimensional pathways linking parental socioeconomic position to their children's cognitive ability and academic track attendance in the secondary school. The sample included twins (N = 4008), respectively ages 11 and 17, and siblings (N = 801). We observed strong genetic influences on cognitive ability, whereas shared environmental influences were much more important for academic tracking. In multilevel analyses, separate dimensions of socioeconomic resources influenced child cognitive ability, controlling parental cognitive ability. Controlling adolescent cognitive ability and parental cognitive ability, parental socioeconomic resources also directly affected track attendance. This indicated that it is crucial to investigate the intertwined influences on educational outcomes in adolescence of both cognitive ability and the characteristics of the family of origin.

Genetic Influences on Hormonal Markers of Chronic HPA Function in Human Hair - CORRIGENDUM.

Cortisol is the primary output of the hypothalamic-pituitary-adrenal (HPA) axis and is central to the human biological stress response, with wide-ranging effects on physiological function and psychiatric health. In both humans and animals, cortisol is frequently studied as a biomarker for exposure to environmental stress. Relatively little attention has been paid to the possible role of genetic variation in heterogeneity in chronic cortisol, in spite of well-studied biological pathways of glucocorticoid function. Using recently developed technology, hair samples can now be used to measure accumulation of cortisol over several months. In contrast to more conventional salivary measures, hair cortisol is not influenced by diurnal variation or transient hormonal reactivity. In an ethnically and socioeconomically diverse sample of 1 070 child and adolescent twins and multiples from 556 unique families, we estimated genetic and environmental influences on hair concentrations of cortisol and its inactive metabolite, cortisone. We identified sizable genetic influences on cortisol that decrease with age, concomitant with genetic influences on cortisone that increase with age. Shared environmental influences on cortisol and cortisone were modest and, for cortisol, decreased with age. Twin-specific, non-shared environmental contributions to cortisol and cortisone became increasingly correlated with age. We find some evidence for sex differences in the biometric contributions to cortisol, but no strong evidence for main or moderating effects of family socioeconomic status on cortisol or cortisone. This study constitutes the first genetic study of hormone concentrations in human hair, and provides the most definitive characterization to-date of age and socioeconomic influences on hair cortisol.

An Investigation of Genetic and Environmental Influences Across the Distribution of Self-Control

Previous research illustrating a robust, negative association between self-control and various forms of delinquent and criminal behavior has resulted in a more concentrated focus on the etiological development of self-control. The current study aims to contribute to this literature using a sample of twin and sibling pairs from the National Longitudinal Study of Adolescent to Adult Health (Add Health) to examine genetic and shared environmental influences across levels of self-control. The results of modified DeFries–Fulker (DF) equations revealed that genetic and shared environmental influences were distributed in a nonlinear pattern across levels of self-control. Subsequent biometric quantile regression models revealed that genetic influences on self-control were maximized in the 50th and 60th percentiles, and minimized in the tails of the distribution. Shared environmental influences were nonsignificant at all examined quantiles of self-control with only one exception. The theoretical importance of utilizing genetically informed modeling strategies is discussed in more detail.

Genetic and environmental etiology of speech and word reading in Chinese

The present study examined the genetic and environmental etiology of the connection between speech and word reading in Chinese. A total of 371 pairs of Chinese twins (278 pairs of monozygotic twins and 93 pairs of same-sex dizygotic twins) were tested on speech discrimination and production, phonological skills, semantic skills, and Chinese word reading at the mean age 7.4years. Results of univariate genetic analyses showed moderate genetic influences on speech, semantic skills, and Chinese word reading, while moderate shared environmental influences on phonological skills. The genetic correlations among all the variables were significant. Results of testing several models on the link between speech and word reading supported a common genetic factor underlying speech, phonological skills, semantic skills, and word reading in Chinese. The present findings suggest that around 50% to 60% of individual differences of speech, semantic skills, and word reading in Chinese are due to genetic factors. Individual differences of phonological skills appear to be relatively less heritable than those in English. This may be partly due to the fact that the Chinese script does not map directly on any segmental phonological information. A single common genetic etiology for speech, phonological skills, semantic skills, and word reading suggests that development of these skills is highly connected.

The Home Environment Shapes Emotional Eating.

Emotional overeating (EOE) is the tendency to eat more in response to negative emotions; its etiology in early life is unknown. We established the relative genetic and environmental influences on EOE in toddlerhood and early childhood. Data were from Gemini, a population-based cohort of 2,402 British twins born in 2007. EOE was measured using the "emotional overeating" scale of the Child Eating Behavior Questionnaire (CEBQ) at 16months and 5years. A longitudinal quantitative genetic model established that genetic influences on EOE were minimal; on the other hand, shared environmental influences explained most of the variance. EOE was moderately stable from 16months to 5years and continuing environmental factors shared by twin pairs at both ages explained the longitudinal association.

Are people with chronic low back pain meeting the physical activity guidelines? A co-twin control study

BackgroundDespite a large amount of research investigating physical activity (PA) levels in people with chronic low back pain (LBP), no study has investigated whether people with chronic LBP are meeting the World Health Organization (WHO) PA guidelines. Furthermore, with genetics and the early shared environment substantially influencing the presence of LBP and PA engagement, these factors could confound the association between LBP and PA and need to be controlled for. PurposeThis study aimed to investigate the association between chronic LBP and meeting the PA guidelines, while controlling for the effects of genetics and early shared environment. DesignThis is a cross-sectional co-twin control study. Patient SampleA cross-sectional analysis was performed on 1,588 twins from the Murcia Twin Registry in Spain with available data on LBP and PA from the 2013 data collection wave. Outcome MeasuresThe exposure and outcome variables in our study were self-reported. Twins reporting a history of chronic LBP were asked follow-up questions to inform on the presence of recent LBP (within the past 4 weeks), previous LBP (no pain within the past 4 weeks), and persistent LBP (no pain-free month in the last 6 months). These were our exposure variables. Our outcome variable was meeting the WHO PA guidelines, which involved at least 75 minutes of vigorous-intensity PA, or at least 150 minutes of moderate-intensity PA per week. MethodsTo investigate the association between chronic LBP and meeting the PA guidelines, we first performed a multivariate logistic regression on the total sample of twins. Co-variables entered the model if the univariate association between the co-variable, and both the exposure and the outcome reached a significance of p<.2. Second, to adjust for the influence of genetics and early shared environment, we performed a conditional multivariate logistic regression on complete twin pairs discordant for LBP. The Murcia Twin Registry is supported by Fundación Séneca, Regional Agency for Science and Technology, Murcia, Spain (08633/PHCS/08 and 15302/PHCS/10) and the Ministry of Science and Innovation, Spain (PSI11560-2009). Funding for this project has also been received from Fundación MAPFRE (2012). The authors declare that there are no conflicts of interest. ResultsThere was a significant inverse association between recent LBP and meeting the PA guidelines (odds ratio [OR]=0.71, p=.034). When controlling for genetics and early shared environment, this association disappeared. There was no association between previous (OR=0.95, p=.779) or persistent LBP (OR=0.78, p=.192) and meeting the PA guidelines. ConclusionTwins with recent LBP are less likely to meet the PA guidelines than those with no history of chronic LBP, highlighting the importance of incorporating PA promotion in the treatment of these individuals. Genetics and early shared environment appear to be confounding the association between LBP and PA, although this needs to be further tested in larger twin samples.

Developmental change in the association between adolescent depressive symptoms and the home environment: results from a longitudinal, genetically informative investigation.

BackgroundDepression is already highly prevalent by late adolescence, indicating that research into its developmental emergence should consider earlier risk factors and environmental contexts. The home environment is a key context for children and adolescents throughout development. However, the nature of relationships that exist between aspects of the home environment and the development of depressive symptoms cannot be assumed. Genetically informative studies have been used to provide insights about the aetiology of such relationships, often finding them to be partly confounded by the influence of children's genes. Here, we investigate developmental change in the aetiology of the association between aspects of the home environment and depressive symptoms at the onset of adolescence.MethodsWe used longitudinal child‐ and parent‐report data from >5,000 twin pairs enrolled in the UK‐representative Twins Early Development Study. Multivariate, genetically sensitive structural equation models were used to decompose latent variance and covariance in depressive symptoms (measured at 12 and 16 years) and aspects of the home environment (at 9 and 14 years) into genetic and environmental influences.ResultsGoing from childhood to adolescence, genetic influences accounted for an increasing proportion of the association [30% (16–42) of r = .44 in childhood; 40% (25–61) of r = .43 in adolescence], at the expense of shared environmental influences, which decreased from 70% (58–83) to 48% (29–62). Unique environmental influences accounted for a significant proportion of the association in adolescence only [12% (06–18)]. Developmental changes could largely be attributed to subtle shifts in the relative importance of stable aetiological factors, rather than the emergence of influences unique to adolescence.ConclusionsThese findings emphasise the importance of developmental and aetiological context in interpreting associations between aspects of the home environment and child emotional outcomes.

Genetic influences on hormonal markers of chronic hypothalamic-pituitary-adrenal function in human hair.

Cortisol is the primary output of the hypothalamic-pituitary-adrenal (HPA) axis and is central to the biological stress response, with wide-ranging effects on psychiatric health. Despite well-studied biological pathways of glucocorticoid function, little attention has been paid to the role of genetic variation. Conventional salivary, urinary and serum measures are strongly influenced by diurnal variation and transient reactivity. Recently developed technology can be used to measure cortisol accumulation over several months in hair, thus indexing chronic HPA function. In a socio-economically diverse sample of 1070 twins/multiples (ages 7.80-19.47 years) from the Texas Twin Project, we estimated effects of sex, age and socio-economic status (SES) on hair concentrations of cortisol and its inactive metabolite, cortisone, along with their interactions with genetic and environmental factors. This is the first genetic study of hair neuroendocrine concentrations and the largest twin study of neuroendocrine concentrations in any tissue type. Glucocorticoid concentrations increased with age for females, but not males. Genetic factors accounted for approximately half of the variation in cortisol and cortisone. Shared environmental effects dissipated over adolescence. Higher SES was related to shallower increases in cortisol with age. SES was unrelated to cortisone, and did not significantly moderate genetic effects on either cortisol or cortisone. Genetic factors account for sizable proportions of glucocorticoid variation across the entire age range examined, whereas shared environmental influences are modest, and only apparent at earlier ages. Chronic glucocorticoid output appears to be more consistently related to biological sex, age and genotype than to experiential factors that cluster within nuclear families.