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Twin Analyses (twin + analysis)
Selected AbstractsNonlinear epigenetic variance: review and simulationsDEVELOPMENTAL SCIENCE, Issue 1 2010Kees-Jan Kan We present a review of empirical evidence that suggests that a substantial portion of phenotypic variance is due to nonlinear (epigenetic) processes during ontogenesis. The role of such processes as a source of phenotypic variance in human behaviour genetic studies is not fully appreciated. In addition to our review, we present simulation studies of nonlinear epigenetic variance using a computational model of neuronal network development. In each simulation study, time series for monozygotic and dizygotic twins were generated and analysed using conventional behaviour genetic modelling. In the results of these analyses, the nonlinear epigenetic variance was subsumed under the non-shared environmental component. As is commonly found in behaviour genetic studies, observed heritabilities and unique environmentabilities increased with time, whereas common environmentabilities decreased. The fact that the phenotypic effects of nonlinear epigenetic processes appear as unsystematic variance in conventional twin analyses complicates the identification and quantification of the ultimate genetic and environmental causes of individual differences. We believe that nonlinear dynamical system theories provide a challenging perspective on the development of individual differences, which may enrich behaviour genetic studies. [source] Mood-Related Drinking Motives Mediate the Familial Association Between Major Depression and Alcohol DependenceALCOHOLISM, Issue 8 2009Kelly C. Young-Wolff Background:, Major depression and alcohol dependence co-occur within individuals and families to a higher than expected degree. This study investigated whether mood-related drinking motives mediate the association between major depression and alcohol dependence, and what the genetic and environmental bases are for this relationship. Methods:, The sample included 5,181 individuals from the Virginia Adult Twin Study of Psychiatric and Substance Use Disorders, aged 30 and older. Participants completed a clinical interview which assessed lifetime major depression, alcohol dependence, and mood-related drinking motives. Results:, Mood-related drinking motives significantly explained the depression-alcohol dependence relationship at both the phenotypic and familial levels. Results from twin analyses indicated that for both males and females, the familial factors underlying mood-related drinking motives accounted for virtually all of the familial variance that overlaps between depression and alcohol dependence. Conclusions:, The results are consistent with an indirect role for mood-related drinking motives in the etiology of depression and alcohol dependence, and suggest that mood-related drinking motives may be a useful index of vulnerability for these conditions. [source] Analysis of Heritability of Hormonal Responses to Alcohol in Twins: Beta-Endorphin as a Potential Biomarker of Genetic Risk for AlcoholismALCOHOLISM, Issue 3 2000J. C. Froehlich Background: Hormonal responses to alcohol have been reported to differ in subjects with and without a family history of alcoholism which suggests that alcohol-induced hormonal changes might be used to identify individuals who are at elevated genetic risk for developing alcoholism. However, before a biological response can be used as a marker of genetic risk for disease, it must first be demonstrated that the response is, in fact, heritable. The present study was designed to determine whether hormonal responses to alcohol are heritable. Methods: The adrenocorticotropic hormone (ACTH), beta-endorphin (,-E), cortisol (CORT), and prolactin (PRL) responses to alcohol were examined in male and female identical (monozygotic or MZ) and fraternal (dizygotic or DZ) twin pairs. Male subjects consumed 0.35g ethanol/kg body weight (BW) and female consumed 0.325 g ethanol/kg BW in each of two alcohol drinking sessions administered 1 hr apar (total dose of 0.7 g/kg BW in males and 0.65 g/kg BW in females). Plasma hormone content was analyzed in samples collected before (resting conditions) and at 15, 60, 75, 120, 180, and 240 min after onset of drinking. Hormonal responses to alcohol were examined with twin analyses using the TWINAN90 program. A separate analysis was performed for each of the four hormones. A subset of subjects from each zygosity was seen on two separate occasions to establish retest reliability. Heritability of hormonal responses to alcohol was estimated using the intraclass correlation approach before and after removing the contribution of covariates that have the potential of influencing the plasma levels of these hormones. Results: Resting plasma levels of all four hormones were within the expected range, and the ,-E, ACTH, and PRL responses to the alcohol challenge evidenced good test-retest reliability. Of the four hormones examined, the only one that showed significant heritability after alcohol drinking was ,-E. Heritability estimates were not altered for any of the four hormones after removal of the variance contributed by covariates, such as gender and age. Conclusions: Taken together with other recent findings, the results suggest that the ,-E response to alcohol may represent a new biomarker that can be used to identify individuals who are at elevated genetic risk for developing alcoholism. [source] An examination of the overlap between genetic and environmental risk factors for intentional weight loss and overeatingINTERNATIONAL JOURNAL OF EATING DISORDERS, Issue 6 2009Tracey D. Wade PhD Abstract Objective: To further our understanding of how intentional weight loss (IWL) and overeating are related, we examined the shared genetic and environmental variance between lifetime IWL and overeating. Method: Interview data were available for 1,976 female twins (both members of 439 and 264 pairs of monozygotic and dizygotic twins, respectively), mean age = 40.61, SD = 4.72. We used lifetime diagnostic data for eating disorders obtained from a semistructured psychiatric telephone interview, examined in a bivariate twin analysis. Both lifetime behaviors were measured on a 3-point scale, where absence of IWL or overeating formed one anchor on the scale and lifetime anorexia nervosa (AN) and bulimia nervosa (BN) formed the opposite anchors, respectively. Results: In line with previous findings, a higher body mass index was significantly associated with the lifetime presence of IWL and/or overeating (odds ratio = 1.13, 95% confidence interval (CI): 1.08,1.19). The best fitting twin model contained additive genetic and nonshared environmental influence influencing both IWL and overeating, with correlations between these influences of 0.61 (95% CI: 0.35,0.92) and 0.24 (95% CI: 0.07,0.42), respectively. Discussion: About 37% of genetic risk factors were considered to overlap between IWL and overeating, and with only 6% of overlap between environmental risk factors. Thus, considerable independence of risk factors was indicated. © 2009 by Wiley Periodicals, Inc. Int J Eat Disord 2009 [source] The effects of social status on biological aging as measured by white-blood-cell telomere lengthAGING CELL, Issue 5 2006L. F. Cherkas Summary Low socio-economic status (SES) is associated with a shortened life expectancy, but its effect on aging is unknown. The rate of white-blood-cell (WBC) telomere attrition may be a biological indicator of human aging. We tested the hypothesis that SES is associated with telomere attrition independent of known risk factors influencing the aging process. We studied 1552 female twins. A venous blood sample was taken from each twin and isolated WBCs used for extraction of DNA. Terminal restriction fragment length (TRFL) was measured. Questionnaire data were collected on occupation, education, income, smoking, exercise, height and weight. Standard multiple linear regression and multivariate analyses of variance tested for associations between SES and TRFL, adjusting for covariates. A discordant twin analysis was conducted on a subset to verify findings. WBC telomere length was highly variable but significantly shorter in lower SES groups. The mean difference in TRFL between nonmanual and manual SES groups was 163.2 base pairs (bp) of which 22.9 bp (,14%) was accounted for by body mass index, smoking and exercise. Comparison of TRFL in the 17 most discordant SES twin pairs confirmed this difference. Low SES, in addition to the harmful effects of smoking, obesity and lack of exercise, appears to have an impact on telomere length. [source] | ||||||||||