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  • 1
    ISSN: 1360-0443
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine , Psychology
    Notes: Aims  To investigate the genetic and environmental influences on tea consumption and their commonalities with coffee consumption; and to further examine the genetic and environmental aetiology of preference for tea/coffee.Design  A classical twin design was used in which the similarity of identical and non-identical twins is compared, enabling estimates of genetic, common environmental and unique environmental influence on the trait.Setting and participants  An Australian population-based sample of 1796 identical (i.e. monozygotic) and 2013 non-identical (i.e. dizygotic) twin pairs aged 16–87 years was studied, roughly three-fifths of whom were female. The sample represented approximately 70% of those approached for study participation.Measurements  As part of a Health and Lifestyle Questionnaire, respondents were asked how many cups of each tea and coffee they consumed per day. Additional measures of ‘total tea and coffee consumption’ and ‘preference for coffee’ were calculated.Findings  Age was positively associated with tea consumption but negatively associated with coffee preference; women consumed more beverages than men, but showed a lower preference for coffee. An inverse relation between tea and coffee consumption—larger in females (−0.41) than males (−0.34)—was supported. This association was mediated entirely by the unique environment in males, and by both the unique environment (68.3%) and genes (31.7%) in females. Tea and coffee drinking were shown to have similar heritabilities (0.46) in males, but tea consumption was influenced by common environmental factors whereas coffee consumption was not. Coffee preference was shown to be influenced by genes (0.42) and the unique environment (0.58).Conclusions  As the patterns of genetic and environmental variation were shown to differ for tea and coffee consumption it may be more informative to retain them as separate measures of caffeine intake in future studies of stimulant use and taste perception.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1469-7610
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine , Psychology
    Notes: Background: In adults, about 40% of the variance in risk of Major Depressive Disorder (MDD) is due to genetic factors, but little data exist on the heritability of youth MDD. The goal of this study was the genetic analysis of MDD in an epidemiologically and genetically representative sample of adolescent female twins.Methods: A sample of 3416 female adolescent twins systematically ascertained from birth records was assessed using a structured telephone interview that included a comprehensive DSM-IV-based section for the diagnostic assessment of MDD. Mean subject age at time of assessment was 15.5 and participation rate exceeded 85%. Genetic modeling was conducted taking into consideration the problem of censoring, i.e., that younger adolescents were not through their period of risk for adolescent onset of MDD.Results: Lifetime self-reported MDD prevalence ranged from 1% under age 12 to 17.4% at age 19 and older. The genetic variance in risk of MDD was 40.4% (95% confidence interval (CI): 23.9–55.1), with the remaining variance explained by non-shared environmental effects 59.6% (95%CI: 44.9–76.1). Shared environmental effects were not significant. A significant recall bias was observed with older respondents on average reporting later onsets for their first episode of MDD.Conclusions: The genetic and environmental contributions to risk of MDD in this representative sample of female adolescent twins are remarkably analogous to findings from adult samples. These results are congruent with a conceptualization of adolescent MDD and adult MDD as having very similar etiologic determinants.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1469-7610
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine , Psychology
    Notes: Little is known about the contribution of genetic and environmental factors to risk for juvenile psychopathology. The Virginia Twin Study of Adolescent Behavioral Development allows these contributions to be estimated. A population-based, unselected sample of 1412 Caucasian twin pairs aged 8–16 years was ascertained through Virginia schools. Assessment of the children involved semi-structured face-to-face interviews with both twins and both parents using the Child and Adolescent Psychiatric Assessment (CAPA). Self-report questionnaires were also completed by parents, children, and teachers. Measures assessed DSM-III-R symptoms of Attention Deficit Hyperactivity Disorder (ADHD), Conduct Disorder, Oppositional Defiant Disorder, Overanxious Disorder, Separation Anxiety, and Depressive Disorder. Factorially derived questionnaire scales were also extracted. Scores were normalized and standardized by age and sex. Maximum likelihood methods were used to estimate contributions of additive and nonadditive genetic effects, the shared and unique environment, and sibling imitation or contrast effects. Estimates were tested for heterogeneity over sexes. Generally, monozygotic (MZ) twins correlated more highly than dizygotic (DZ) twins, parental ratings more than child ratings, and questionnaire scales more highly than interviews. DZ correlations were very low for measures of ADHD and DZ variances were greater than MZ variances for these variables. Correlations sometimes differed between sexes but those for boy-girl pairs were usually similar to those for like-sex pairs. Most of the measures showed small to moderate additive genetic effects and moderate to large effects of the unique individual environment. Measures of ADHD and related constructs showed marked sibling contrast effects. Some measures of oppositional behavior and conduct disorder showed shared environmental effects. There were marked sex differences in the genetic contribution to separation anxiety, otherwise similar genetic effects appear to be expressed in boys and girls. Effects of rater biases on the genetic analysis are considered. The study supports a widespread influence of genetic factors on risk to adolescent psychopathology and suggests that the contribution of different types of social influence may vary consistently across domains of measurement.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1469-7610
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine , Psychology
    Notes: We introduce an overlapping cohort sequential longitudinal study of behavioral development and psychopathology in a representative sample of 1412 pairs of twins aged 8 through 16 years. Multiple phenotypic assessments involve a full psychiatric interview with each child and each parent, and supplementary parental, teacher, and child interview material and questionnaires. For the first wave of assessments, the numbers of reported DSM-III-R symptoms of Major Depressive Disorder (MDD), Separation Anxiety Disorder (SAD), Overanxious Disorder (OAD), Oppositional Defiant Disorder (ODD), Conduct Disorder (CD), and Attention Deficit Hyperactivity Disorder (ADHD), assessed through interviews, confirm patterns of age and sex trends found in other epidemiological samples, but underscore their dependence on whether the child or the parent is the informant. Correlations across domains for symptoms reported by the same informant are often as large as correlations across informants for the same domain of symptoms. Factor analyses of these symptom counts, taking account of informant view and unreliability of assessment, show the high degree of correlation between SAD and OAD, between MDD and OAD, and between CD and ODD. ADHD symptoms are relatively independent of the other domains, but show moderate correlations with CD, ODD, and MDD. Factorially derived dimensional questionnaire scales, based on child, parental, and teacher reports, show patterns of relationship to symptom counts consistent with both convergent and discriminant validity as indices of liability to clinical symptoms. Across informants, questionnaire scales provide as good a prediction of symptoms as do clinical interviews. Multitrait-multimethod confirmatory factor analysis reveals the patterns of relationship between symptoms of psychiatric disorder in children taking due account of informant and unique sources of variance. Gender differences are consistent within the correlated clusters of ODD/CD and MDD/SAD/OAD, although there are disorder-specific age trends. There are large informant-specific influences on the reporting of symptoms in clinical interviews. Dimensional questionnaire scales provide a useful source of additional information. In subsequent analyses of genetic and environmental etiology of childhood psychopathology we must expect that results may differ by informant and method of assessment. Multivariate and developmental analyses that explore the sources of these differences will shed new light on the relationship between genetic and environmentally influenced vulnerability and the manifestation of psychopathology in specific circumstances.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1469-7610
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine , Psychology
    Notes: Background: The goal of this study is to gauge the consistency of Attention Deficit/Hyperactivity Disorder (ADHD) latent class models that are generated by different informants such as adolescents and parents. The consistency of adolescent-derived latent classes from two different samples was assessed and these results were then compared to the class structure generated by parent-report ADHD information. Methods: Self-reported DSM-IV Criterion A ADHD symptoms of 497 adolescent males from a population-based twin study in the state of Missouri (USA) were subjected to principal components and latent class analysis, and findings were compared to previous results obtained from identical analyses using an adolescent sample from Porto Alegre, Brazil (N= 483). Results: The bi-dimensional structure of self-reported ADHD symptoms was similar for both male adolescent groups, but explained less than 40% of the symptom variance in either sample. Two factors, one with loadings on inattention symptoms only and the other with loadings on hyperactive-impulsive symptoms only, were identified in the Missouri sample. Specific ADHD latent classes did not replicate well across the Missouri and Brazilian samples, and both groups were characterized by the presence of several combined symptom classes but few inattentive or hyperactive-impulsive classes. Conclusions: While adolescent-report information across two different cultures can at least in part reproduce the two-factor structure of ADHD, results from latent class analysis suggest that adolescent reporting on their own symptoms is markedly different from the type of information parents provide about ADHD symptoms in their offspring. The current findings indicate that if male adolescents endorse any ADHD symptoms there is a tendency for them to report combined type problems.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1469-7610
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine , Psychology
    Notes: Background:  Findings from family and twin-based studies of Attention Deficit/Hyperactivity Disorder (ADHD) have indicated that inattentive and combined subtypes cluster together among sibling pairs who both express ADHD symptoms. The current report examines the familial clustering of ADHD subtypes, defined according to latent class and DSM-IV criteria, in a general population sample of 2,848 Australian twins, 1,013 of their non-twin siblings and 4,036 female twins from Missouri, USA. Significant clustering of DSM-IV inattentive and combined subtypes, and significant clustering of the same latent classes among siblings was predicted.Method:  Logistic regression was used to assess 1) the clustering of same and different subtype combinations among twin and twin-sibling pairs and 2) whether genetic influences contribute significantly to the observed patterns of subtype combinations among siblings.Results:  With the exception of the DSM-IV hyperactive-impulsive subtype and the severe hyperactive-impulsive latent class, all other sibling DSM-IV and latent class ADHD subtypes consistently exhibited significant same-subtype clustering with MZ probands, DZ probands and their siblings in both samples. Furthermore, a significant genetic influence contributing to subtype concordance was detected for every DSM-IV subtype excluding hyperactive-impulsive, and for all eight latent classes. While some instances of significant different-subtype clustering among siblings was observed across both classification systems and samples, the particular subtype combinations involved were largely inconsistent across samples and no significant genetic influences contributing towards these discordant subtype combinations were detected.Conclusions:  For both DSM-IV and latent class subtypes, the overall pattern of findings in both samples indicated significant familial clustering of same-subtype combinations and significant genetic influences contributing to these patterns of subtype concordance, despite important sample differences. These findings further extend previous work and are most consistent with the presence of multiple independent forms of ADHD.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1469-7610
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine , Psychology
    Notes: Background: Previous efforts to subtype Attention-Deficit/Hyperactivity Disorder (ADHD) using latent class analysis (LCA) applied to DSM-IV symptom profiles of adolescent female twins from Missouri (USA) have identified distinct classes within the domains of inattention, hyperactivity-impulsivity and combined-type problems. The objective of the current report is to determine if the latent class structure of ADHD subtypes can be replicated in a culturally distinct sample of female and male Australian twins. Method: LCA was applied to parent-report DSM-IV ADHD symptom profiles of N=2,848 child and adolescent Australian twins and compared to North American findings. Separate models were fitted for females (N=1,432) and males (N=1,416). Results: The most congruent latent ADHD classes across samples included a non-symptomatic class, three mild-moderate and two severe classes. Also present within samples was a rare hyperactive-impulsive class and a unique class, the structure of which was idiosyncratic across samples. Mean symptom endorsement and individual symptom endorsement probabilities for each of the stable classes were similar across samples. Consistent with previous findings, there was substantial overlap between the DSM-IV inattentive and combined subtypes with the severe inattentive and severe combined latent classes. However, DSM-IV inattentive and combined subtypes were distributed over several latent classes in each sample, and a substantial proportion of individuals with no DSM-IV diagnosis were also assigned to these severe classes. Conclusions: Results from LCA using an Australian twin sample replicate six of the eight latent class subtypes previously reported using Missouri female twins and extend the findings to male twins. LCA and DSM-IV systems of ADHD classification identify different phenotypic groups, and the basis of this disparity merits further investigation.
LCA: latent class analysis; ADHD: Attention-Deficit/Hyperactivity Disorder
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 1360-0443
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine , Psychology
    Notes: Aims  To investigate the role of measured risk factors and the influence of genetic and environmental factors on regular cigarette smoking.Design  Members of monozygotic and dizygotic, including unlike-sex twin pairs (n = 6257) from a young adult cohort from the Australian Twin Registry.Methods  Cox proportional hazards models were used to determine whether putative risk factors were significantly associated with regular cigarette smoking. Risk factors were classified into four tiers: tier 1 (parental history, including parental education, alcoholism and cigarette smoking), tier 2 (early home and family influences), tier 3 (early life events, e.g. trauma) and tier 4 (psychiatric symptoms/disorders with onset prior to 14 years), after controlling for gender, zygosity and their interactions. Genetic models were fitted to examine the heritability of smoking behavior before and after controlling for significant covariates from the four tiers.Findings  Parental history of cigarette smoking and alcoholism, parental closeness and home environment, as well as incidence of childhood sexual abuse or other trauma, a history of early onset panic attacks and conduct problems were associated with regular cigarette smoking. Important age interactions were found, particularly for family background risk factors. Regular cigarette smoking was moderately heritable, even after accounting for significant covariates.Conclusions  Several measured risk factors are associated with regular smoking. While some of the genetic influences on regular smoking may be shared with these risk factors, a significant proportion of the genetic vulnerability to regular smoking is phenotype-specific.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 1573-3297
    Keywords: Twin studies ; equal-environment assumption ; psychiatric disorders ; depression ; alcoholism ; anxiety disorders
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Psychology
    Notes: Abstract The traditional twin method is predicated on the equal-environment assumption (EEA)—that monozygotic (MZ) and dizygotic (DZ) twins are equally correlated in their exposure to environmental events of etiologic importance for the trait under study. In 1968, Scarr proposed a test of the EEA which examines the impact of phenotypic similarity in twins of perceived versus true zygosity. We apply this test for the EEA to five common psychiatric disorders (major depression, generalized anxiety disorder, phobia, bulimia, and alcoholism), as assessed by personal interview, in 1030 female-female twin pairs from the Virginia Twin Registry with known zygosity. We use a newly developed model-fitting approach which treats perceived zygosity as a form of specified familial environment. In 158 of the 1030 pairs (15.3%), one or both twins disagreed with the project-assigned zygosity. Model fitting provided no evidence for a significant influence of perceived zygosity on twin resemblance for any of the five disorders. Although limited in power, these results support the validity of the EEA in twin studies of psychiatric disorders.
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 1573-3297
    Keywords: Child-rearing ; socialization ; coevolution ; sociobiology ; twin design ; Parental Bonding Instrument
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Psychology
    Notes: Abstract A large sample of adult twins (1117 pairs), who were concordant for having had children were asked to report on their child-rearing practices. A 14-item version of the Parental Bonding Instrument (PBI) was used to assess rearing practices of parent twins. The two factors of Care and Overprotection, commonly found in other studies, were recovered from this analysis of the PBI's parent form. Model-fitting analyses indicate that human parental behavior is under significant genetic influence. Findings further suggest that this influence is sex limited, with a higher heritability in mothers than in fathers and that it may result partly from the expression of dominant genes. For both PBI factors and both parents, the best-fitting models invariably assumed sex-limited genetic effects and unique environmental influences only. Broad heritability ranged from 19% (father overprotection) to 39% (mother care). These results are interpreted in the broader perspective of gene-culture theory.
    Type of Medium: Electronic Resource
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