Adoption study

Abstract: Two issues that complicate behavioral genetic analyses are the interaction and correlation between genetic and environmental influences. In this report, the effects of genotype-envi ronment interaction and correlation on behavioral genetic studies (twin and adoption studies) are examined. The analysis suggests that genotype-environment interaction may bias twin study estimates of genetic and environmental influence, but need not affect adoption studies. On the other hand, genotype-environment correlation may affect both twin and adoption study estimates of genetic and environmental influence, the direction of the effect depending on the sign of the correlation. Finally, new tests of genotypeenvironment interaction and correlation, using adoption data, are proposed.

Abstract: We examined the contributions of genetic factors and the family environment to human fatness in a sample of 540 adult Danish adoptees who were selected from a population of 3580 and divided into four weight classes: thin, median weight, overweight, and obese. There was a strong relation between the weight class of the adoptees and the body-mass index of their biologic parents - for the mothers, P less than 0.0001; for the fathers, P less than 0.02. There was no relation between the weight class of the adoptees and the body-mass index of their adoptive parents. Cumulative distributions of the body-mass index of parents showed similar results; there was a strong relation between the body-mass index of biologic parents and adoptee weight class and no relation between the index of adoptive parents and adoptee weight class. Furthermore, the relation between biologic parents and adoptees was not confined to the obesity weight class, but was present across the whole range of body fatness - from very thin to very fat. We conclude that genetic influences have an important role in determining human fatness in adults, whereas the family environment alone has no apparent effect.

Abstract: Background. To clarify the role of genetic and environmental risk factors in alcohol use disorders (AUDs), we performed a meta-analysis of twin and adoption studies and explored the impact of sex, assessment method (interview v. hospital/population records), and study design (twin v. adoption study) on heritability estimates. Method. The literature was searched for all unique twin and adoption studies of AUD and identified 12 twin and five adoption studies. The data were then reconstructed and analyzed using ordinal data full information maximum likelihood in the OpenMx program. Heterogeneity was tested with likelihood ratio tests by equating the parameters across studies. Results. There was no evidence for heterogeneity by study design, sex or assessment method. The best-fit estimate of the heritability of AUD was 0.49 [95% confidence interval (CI) 0.43–0.53], and the proportion of shared environmental variance was 0.10 (95% CI 0.03–0.16). Estimates of unique environmental proportions of variance differed significantly across studies. Conclusions. AUD is approximately 50% heritable. The multiple genetically informative studies of this syndrome have produced consistent results that support the validity of this heritability estimate, especially given the different potential methodological weaknesses of twin and adoption designs, and of assessments of AUD based on personal interviews v. official records. We also found evidence for modest shared environmental effects suggesting that environmental factors also contribute to the familial aggregation of AUDs.

Abstract: Background:Weconductedasibling/twin/adoptionstudy of substance initiation, use, and problem use, estimating the relative contribution of genetic and environmental influences on these phenotypes in adolescents. Methods:The participants were 345 monozygotic twin pairs,337dizygotictwinpairs,306biologicalsiblingpairs, and 74 adoptive sibling pairs assessed by the Colorado CenterfortheGeneticsandTreatmentofAntisocialDrug Dependence,DenverandBoulder.Theinitiation,use,and problem use of tobacco, alcohol, marijuana, and other illicit drugs were assessed. Tetrachoric correlations were computed for each group, and univariate model-fitting analyses were conducted. Results: There were moderate to substantial genetic influences, with the exception of alcohol use and any drug use, and modest to moderate shared environmental influences on substance initiation, use, and problem use. For alcoholandanydrug,heritabilitywashigherandthemagnitude of shared environmental influences was lower for problem use than for initiation or use. Environmental influences shared only by twin pairs had a significant effect on tobacco initiation, alcohol use, and any drug use. For tobacco use, tobacco problem use, and marijuana initiation, heritability was higher and the magnitude of shared environmentalinfluenceswaslowerinfemalethaninmale adolescents. There was no evidence for sex-specific genetic or shared environmental influences on any variable. Conclusions: The moderate to substantial heritabilities found for adolescents in the present study are comparable to those found in twin studies of adult substance use and substance use disorders. The finding that problem use is more heritable than initiation and use is alsoconsistentwiththeresultsofadulttwinstudies.The significance of environmental influences shared only by twinpairsontobaccoinitiation,alcoholuse,andanydrug use suggests the influences of peers, accessibility of substances, and sibling interaction. Arch Gen Psychiatry. 2003;60:1256-1264