Sample Of Australian Twins Research Articles

Genetic influences on endometriosis in an Australian twin sample

To investigate the prevalence of and twin pair concordance for endometriosis. A questionnaire survey incorporating validation. An Australia-wide volunteer sample of female monozygotic (MZ) and dizygotic (DZ) twin pairs from the Australian National Health and Medical Research Council Twin Register. Twins were selected only on the basis of previous participation in twin research. Questionnaires were sent to 3,298 individuals. Information was requested from physicians named by consenting twins. Reported endometriosis, validated where possible by pathology or surgical report. Three thousand ninety-six (94%) of the twins and 145 (82%) of the physicians responded to the survey. Two hundred fifteen twins reported endometriosis, for a prevalence rate of .07 among question respondents. Tetrachoric twin pair correlations for self-reported endometriosis (MZ: n = 854 and DZ: n = 493) were rMz = .46+/-.09 and rDz = .28 +/-.13. When available medical and pathology reports were included, they changed to rMz =.52 +/-.08 and rDZ = .19+/-.16, suggesting that 51% of the variance of the latent liability to endometriosis may be attributable to additive genetic influences. These findings support the hypothesis that genes influence liability to endometriosis.

The Short Interpersonal Reactions Inventory, Self-regulation and differentiation scales in an older Australian twin sample

Abstract An English translation of the Differentiation and Self-regulation extension scales has been used in conjunction with a reduced form of the Short Interpersonal Reactions Inventory (SIRI) in a sample of 2844 Australian twins aged over 50. Significant correlation was found between Type 1 (cancer-prone) and Type 2 (coronary heart disease prone), and between Self-regulation and Type 4 (healthy). The low correlations reported in other studies between the two alternative subscales of Type 4 are also observed. The Differentiation scales of Agitation and Inhibition were not found to significantly improve discrimination between Grossarth-Maticek's personality Type 1 and 2 subjects in this study.

Longitudinal genetic analysis of menstrual flow, pain, and limitation in a sample of Australian twins.

Genetically informative longitudinal data about menstrual disorders allow us to address the extent to which the same genetic risk mechanisms are operating throughout the reproductive life cycle. We investigate the relative contributions of genes and environment to individual differences in menstrual symptomatology reported at two waves, 8 years apart, of a longitudinal Australian twin study. Twins were questioned in 1980-1982 and 1988-1990 about levels of menstrual pain, flow, and perceived limitation by menses. Longitudinal genetic analysis was based on 728 pairs (466 MZ and 262 DZ) who were regularly menstruating at both survey waves. A bivariate Cholesky model was fitted to the two-wave data separately for flow, pain, and limitation variables. The baseline model comprised common genetic and environmental factors influencing responses at both waves and specific effects influencing only the second-wave response. We also included age as a covariate in the model. Proportions of the longitudinally stable variance in menstrual flow, pain, and limitation attributable to genetic and individual environmental effects were calculated for the best-fitting models. Genetic factors accounted for 39% of the longitudinally stable variation in menstrual flow, 55% for pain, and 77% for limitation. The remaining stable variance was due to individual environmental factors (61, 45, and 23%, respectively). Therefore the stable variance over the 8-year interval was largely environmentally influenced for menstrual flow, was approximately equally determined by genetic and by nonshared environmental influences in the case of pain, and was due almost entirely to genetic influences for limitation by periods. We demonstrate for the first time that the same genetic influences are operative throughout the reproductive life span.

Family Characteristics and the Returns to Schooling: Evidence on Gender Differences from a Sample of Australian Twins

Data from the Australian Twins Survey are analysed in order to compare the relative importance of the role of family background as a mediating influence on the relationship between schooling and income for males and females. The analysis reveals that family background is a considerably greater influence on males than on females. This finding is consistent with a greater screening role for education in the case of females and with a process of intergenerational transmission of inequality for males but not for females.

Social contact, social attitudes, and twin similarity.

The nature of the relationship between social contact and attitude similarly between twins was investigated using longitudinal data from a sample of Australian twins. Earlier research has suggested that social attitudes are not explained solely by shared environment; rather there are both genetic and environmental components that explain variance in social attitudes. Using three types of analyses we investigated the magnitude of the relationship and the direction of causation between attitude similarity and social contact. Longitudinal analysis of within-pair variance by level of contact suggests that attitude similarity leads to contact among the females and that similarity is both genetically and environmentally based. Analyses using a crosslag regression model suggest that similarity causes contact among MZ females. Biometrical analyses indicate differences in direction of causation for males and females. Among females, both genetic and shared environmental parameter estimates could be equated across contact groups, suggesting little relationship between contact and similarity. Among males, findings of smaller estimated heritability in the high-contact group suggest that similarity causes contact. However, an increased estimate of the contribution of shared environmental variance in the high-contact males could additionally suggest that contact leads to similarity.

Agenesis of permanent maxillary lateral incisors in South Australian twins.

The frequency of agenesis of maxillary lateral incisors (I2) in a sample of South Australian twins was determined, and associations with gender, zygosity, birthweight and dental crown size were investigated. Ten of the 446 twins examined (2.24 per cent) displayed agenesis of one or both I2, a similar frequency to that reported for Australian singletons. Seven of the ten affected individuals were monozygous female twins, including two pairs, while the three affected dizygous twins were each from different male twin pairs. Five pairs of monozygous twins were identified who displayed varying expressions of normal, small, peg-shaped or missing I2. These twin pairs displayed disparate birthweights suggesting they may have been mono-chorionic. These findings are consistent with a multifactorial threshold model linking size and number of I2 with developmental influences modifying phenotypic expression in those monozygous twins whose genetic predisposition places them near to the threshold for agenesis.

A psychometric evaluation of the Short Interpersonal Reactions Inventory (SIRI) in an Australian twin sample

Abstract The Short Interpersonal Reactions Inventory [SIRI (Grossarth-Maticek, Eysenck, Vetter & Schmidt, Topics in Health, 1988)] is a questionnaire designed to measure personality traits predisposing to disease, notably ischaemic heart disease and cancer. It has been criticized by several authors in terms of design, scoring and validity. In a sample of 762 Australian twins taking part in a genetic study of asthma, we have examined the psychometric properties of the SIRI, and its relationship with the Eysenck Personality Questionnaire. Asthma was not significantly associated with any of the items or subscales of the SIRI. Scores on the seven subscales as defined by the SIRI authors (Types 1–3, 4 + and 4−, 5–6) were heavily skewed or truncated in six cases. Disturbingly, the two alternative forms of the Type 4 subscale were poorly intercorrelated (r = 0.17). A factor analysis using polychoric correlations partially replicated these subscales, but with important differences, similar to those found by other authors (Ranchor, Sanderman & Bouma, Personality and Individual Differences, 14, 483–484 1992). Scores on the SIRI and EPQR/S personality types were found to correlate broadly, as predicted by Eysenck (Perceptual and Motor skills, 71, 216–218, 1990). Attempts to assign each subject to a single major type were unsuccessful, whether by maximum subscale score, or membership of the upper quartile of a subscale distribution. Finally, we found that the questionnaire could be shortened from 70 to 25 items with little loss of internal reliability. We conclude that the SIRI has a number of shortcomings as currently formulated, but that it may serve as the basis for shorter instruments with superior internal and construct validity.

Nature, nurture, and conservatism in the Australian Twin Study.

Church attendance, educational level, and six conservatism scales were the subject of a multivariate behavior-genetic analysis by Truett et al. (Behav. Genet. 22, 43-62, 1992), based on responses from a large sample of adult Australian twins. These data are here analyzed in a different way to elicit general conservatism factors in the genetic, shared environmental, and unshared environmental covariation. The general genetic factor appears mainly to reflect intellectual sophistication; the general environmental factors, religious affiliation. These factors are similar, although not identical, for men and women.

The FIGIJ Newsletter, No. 2, June 1993

This study uses a sample of young Australian twins to examine whether the findings reported in [Ashenfelter, Orley and Krueger, Alan, (1994). ‘Estimates of the Economic Return to Schooling from a New Sample of Twins’, American Economic Review, Vol. 84, No. 5, pp.1157–73] and [Miller, P.W., Mulvey, C and Martin, N., (1994). ‘What Do Twins Studies Tell Us About the Economic Returns to Education?: A Comparison of Australian and US Findings’, Western Australian Labour Market Research Centre Discussion Paper 94/4] are robust to choice of sample and dependent variable. The economic return to schooling in Australia is between 5 and 7 percent when account is taken of genetic and family effects using either fixed-effects models or the selection effects model of Ashenfelter and Krueger. Given the similarity of the findings in this and in related studies, it would appear that the models applied by [Ashenfelter, Orley and Krueger, Alan, (1994). ‘Estimates of the Economic Return to Schooling from a New Sample of Twins’, American Economic Review, Vol. 84, No. 5, pp.1157–73] are robust. Moreover, viewing the OLS and IV estimators as lower and upper bounds in the manner of [Black, Dan A., Berger, Mark C., and Scott, Frank C., (2000). ‘Bounding Parameter Estimates with Nonclassical Measurement Error’, Journal of the American Statistical Association, Vol. 95, No.451, pp.739–748], it is shown that the bounds on the return to schooling in Australia are much tighter than in [Ashenfelter, Orley and Krueger, Alan, (1994). ‘Estimates of the Economic Return to Schooling from a New Sample of Twins’, American Economic Review, Vol. 84, No. 5, pp. 1157–73], and the return is bounded at a much lower level than in the US.

Fitting genetic models to Carabelli trait data in South Australian twins.

This study aimed to clarify genetic and environmental contributions to Carabelli trait variation on permanent first molar teeth in a large sample of South Australian twins. Estimates of polychoric correlations were obtained between pairs of monozygous (MZ) and dizygous (DZ) twins for Carabelli data and various gene-environment models fitted by a weighted least-squares approach. The favored model included additive genetic effects together with both a general environmental component and an environmental effect specific to each side. An estimate of heritability around 90% indicated a very strong genetic contribution to observed variation. The pattern of correlations for MZ and DZ data suggested that further studies involving other types of relatives would be worthwhile for detection of possible non-additive genetic effects of dominance or epistasis.