Biomedical subjects

G T Macaskill

Publications and source records attributed to G T Macaskill.

9 recordsLinked to original sources

PubMed1994

Genetic and environmental variation in Eysenck Personality Questionnaire scales measured on Australian adolescent twins.

The Eysenck Personality Questionnaire was administered to 1400 Australian twin pairs aged 11 to 18, and the data were analyzed by a multivariate normal model using the software FISHER. For each scale, attempts were made to transform to normality, about a mean modeled separately for each sex as a quadratic function of age. Variances and covariances were estimated for each sex-zygosity group as a monotone function of age. Evidence for genetic sources of variation were assessed in part by fitting models which allowed for age-dependent, sex-specific, and correlated additive genetic factors, and age-dependent and sex-specific environmental factors, under the assumption that effects of environmental factors common to twin pairs are independent of zygosity. Evidence for genetic factors independent of age and sex was most compelling for Psychoticism and Neuroticism. For Extraversion, if genetic factors exist they would be mostly sex-specific and age-dependent. For the Lie scale there was evidence for, at most, a small component of genetic variation.

Adolescent↗

PubMed1993

Blood pressure in subjects from rural Greece, comparing individuals migrating to Melbourne, Australia with non-migrant relatives.

The aim of the study was to compare the systolic and diastolic blood pressures in 525 individuals who had migrated from rural Greece to Melbourne, Australia with those in 367 nonmigrant relatives (all aged 30 to 59 years and still living in the source area), and to relate any differences to previously identified correlates of BP. This migrant family design offers enhanced environmental heterogeneity while controlling in large part for genetic and other familial factors. Migrating siblings differed from nonmigrating siblings on some variables determined at the time of migration but these were not independently associated with BP. Migrants had been in Australia for an interquartile range of 19 to 25 years. DBP was higher in migrants by 4.57 (+/- 0.97) mmHg for males and 2.66 (+/- 0.86) mmHg for females. SBP was not different at age 30 years but increased more steeply with age in the migrants: 0.89 (+/- 0.17) mmHg/yr vs. 0.41 (+/- 0.13) mmHg/yr in males and 1.18 (+/- 0.14) mmHg/yr compared with 0.83 (+/- 0.15) mmHg/yr in females. Significant associations, independent of age, were found only with body mass index and ambient temperature at the time and place of measurement. There was no consistent association with alcohol despite a wide range of exposures, with dietary and psychosocial variables, or with length of residence independent of age. The higher body mass index of and lower ambient temperatures for migrants accounted for differences in mean DBP but not in SBP. Proportions defined as hypertensive were similarly associated only with migrant status, body mass index and temperature. Pressures in Greece were substantially below predictions derived from the Intersalt data set, suggesting unidentified protective factors.

Adult↗

PubMed1992

Pedigree analysis of blood pressure in subjects from rural Greece and relatives who migrated to Melbourne, Australia.

Diastolic blood pressure readings taken in 1983-1984 on 1,474 Greek individuals (628 living on the island of Levkada, 846 relatives having migrated to Melbourne, Australia) from 204 two generational pedigrees were analysed. Blood pressure was regressed as a quadratic in age by sex and migrant status, and on temperature. Variance increased with age and was greater in migrant males. The covariance between relatives in different countries was significant. Variation was modeled by a multivariate normal model for pedigree analysis in terms of genetic effects, a common environment effect, and effects particular to an individual. The genetic component was 25.9 mm Hg2, independent of sex and migrant status. Importantly, the common environment component was not significant. The third component was greatest in migrant males. Spouse correlation was -0.09 (SE = 0.03). Exclusion of 86 individuals who reported currently receiving medication for elevated blood pressure stabilised the variance and decreased the genetic component. The data suggest that familial aggregation of diastolic blood pressure is due to genetic factors which produce the same variation in males and females, living on Levkada or in Melbourne. Nongenetic factors explain the greater variation in blood pressure of migrant males living in Melbourne.

Adolescent↗

PubMed1992

Alcohol use, smoking habits and the Adult Eysenck Personality Questionnaire in adolescent Australian twins [corrected].

In 1988, questionnaires were received from 1,400 twin pairs (17% MZM, 23% MZF, 17% DZM, 19% DZF, 24% DZO) aged 11 to 18, registered with the Australian NHMRC Twin Registry. Twins reported independently on themselves and on the perceived behaviour of their parents, siblings and friends. For smoking and for drinking in the previous month, the prevalence was modelled as a logistic function of age, sex, perceived smoking or drinking behaviour of family and friends, and the Adult Eysenck Personality Questionnaire (AEPQ) scales. Strengths of association were: family behaviour, odds ratio (OR) < or = 2; Extraversion and Psychoticism, interquartile OR approximately 1.6; behaviour of friend, OR approximately 3 to 6. Twin associations were represented by odds ratios. For smoking they were 16 in MZ and 7 in DZ same-sex pairs, and 3 in DZO pairs. Although the former is consistent with genetic factors determining adolescent smoking behaviour, the reduced association in DZO pairs and strong association with smoking by friends argue to the contrary. For drinking, twin odds ratios were 11 in MZM, MZF and DZF pairs, and 4 in DZM and DZO pairs, consistent with genetic factors determining alcohol use in male but not female, adolescents. Twin odds ratios were not influenced by adjustment for the AEPQ scales; this does not support the hypothesis that genetic factors which determine personality also determine smoking or drinking behaviour during adolescence [corrected].

Adolescent↗

PubMed1991

Longitudinal analysis of lung function growth in healthy children and adolescents.

Lung function and height in 242 8-yr-old and 299 12-yr-old children without known or suspected predisposition to lung disease were measured annually over 6 and 8 yr, respectively. Growth of forced expiratory volume in 1 s (FEV1), vital capacity, and expiratory flow after expiring 50% of vital capacity were statistically modeled by age and height by use of a multivariate normal model for longitudinal data. This method has the flexibility to fit an appropriate (not necessarily linear) mathematical description of average lung function while concurrently modeling the covariance between measures on the same individual. Differences in lung function growth between girls and boys, pre- and post-puberty, showed that girls had a steadier though less pronounced increase in lung function with height. In boys, before puberty there was deficit in lung volume relative to height (not evident in girls), which was compensated for by rapid growth after puberty. The standard error of FEV1 predictions based on current height and age were more than halved when measurements of FEV1, age, and height taken 1 yr before were incorporated. We found evidence for dysanaptic growth in childhood. Fitted models have application to early detection of departures from healthy lung function.

Adolescent↗

PubMed1991

Genetic factors in bone turnover.

Genetic factors are major determinants of adult bone density, however, it is unknown how these effects may be mediated. Since bone mineral density is the net result of bone formation and bone resorption we studied biochemical indices of bone formation (serum osteocalcin) and resorption [fasting urinary calcium:creatinine (Ca/Crt) and hydroxyproline:creatinine (OH/Crt)] in adult female twins; 39 monozygotic (MZ) and 31 dizygotic (DZ) twin pairs (age, mean +/- SEM, MZ: 51.1 +/- 1.5 yrs; DZ: 46.5 +/- 1.5 yrs, P = NS). Of these subjects, 18 MZ twin pairs and 10 DZ twin pairs were postmenopausal. The MZ twin pair correlations (rMZ) for each index of bone turnover exceeded that between DZ pairs (rDZ), but this difference was only significant for osteocalcin (rMZ = 0.81, rDZ = 0.21, P less than 0.001). Similarly, in the postmenopausal group examined alone, the rMZ (r = 0.84) for serum osteocalcin was significantly greater than rDZ (r = -0.003, P less than 0.03). These osteocalcin data imply that 80% of the variance in serum osteocalcin could be explained by genetic factors. Although genetic effects on fasting urinary hydroxyproline:creatine and calcium:creatinine were not demonstrable, these indices may be less precise and specific. The data indicate that circulating osteocalcin, and therefore bone formation, is strongly genetically determined. These studies suggest at least one of the mechanisms of the genetic effect on bone mass relates to the regulation of bone turnover.

Adult↗

PubMed1990

A family study of panic disorder: reanalysis using a regressive logistic model that incorporates a sibship environment.

Previous analysis of affection status in parents and siblings of 117 probands with panic disorder by a log-linear model for binary pedigree data found a common concordance across biological first-degree relatives and no spouse association [Hopper JL, Judd FK, Derrick PL, Burrows GD: Genet Epidemiol 4:33-41, 1987]. In this paper the data were reanalyzed using a regressive logistic model that modelled both vertical transmission and a shared sibship environment. Ascertainment correction was made by a) an "ascertainment assumption-free" procedure, following Ewens and Shute [Theor Pop Biol 30:388-412, 1986] and compared with b) complete ascertainment and c) single ascertainment. Under every scheme there was evidence for vertical transmission from parents to offspring. Inclusion of a sibship environment gave an improved fit, suggesting that vertical transmission alone may not be sufficient to explain the familial aggregation observed in these families. The effects of an affected parent, of the postulated environmental factor (present for all siblings if it was present for one sibling), and of the prevalence of the rare environmental factor were estimated and found to be roughly similar under the different schemes. Model predictions of lifetime prevalence were consistent with other population-based studies. Under the same assumption-free method, standard errors approximately doubled and computation time increased compared with the other ascertainment schemes that made specific, although not necessarily correct, assumptions. The regressive logistic model used less computation time and gave greater insight into the pattern of familial aggregation than did the previous modelling.

Adult↗

PubMed1990

Twin concordance for a binary trait: III. A bivariate analysis of hay fever and asthma.

Self-reported histories of hay fever and asthma were obtained from 3,808 pairs of adult twins 18 years and over registered with the Australian National Health Medical Research Council Twin Registry (1232 MZF, 567 MZM, 751 DZF, 352 DZM, 906 DZO). The prevalence of hay fever and asthma was 0.32 and 0.13, respectively, with little variation with zygosity, sex, and age. The associations between twin pairs for these two traits were analysed, under the assumption of constant prevalences, as a special case of a log-linear model for binary traits in pedigrees using the statistical package GLIM. The model assumption that there are no second- or higher-order interactions was tested in the 2 X 2 X 2 X 2 table of twin by disease outcomes without revealing strong evidence of departure, even in this large data set. The log-linear modelling showed that only three first-order interactions, namely 1) between hay fever in a twin pair, 2) asthma in a twin pair, and 3) hay fever and asthma in the same twin, were necessary to describe the data. The first two interaction terms were significantly larger in identical pairs; the third was independent of zygosity. Under this parsimonious model, there was a significant difference between identical and fraternal pairs in marginal correlation, both in asthma and hay fever, and in the cross-correlation between hay fever in one twin and asthma in the other. This suggests that genetic factors are implicated in both hay fever and asthma and that some of these genetic factors are common (at least among a subgroup of individuals) to both traits.

Adolescent↗

PubMed1990

Incorporation of twins in the regressive logistic model for pedigree disease data.

Segregation and twin disease concordance analyses have assumed a theoretical underlying liability following a multivariate normal distribution. For reasons of computation, of incorporation of measured explanatory variables, and of testing of fit and assumptions, newer analytical methods are being developed. The regressive logistic model (RLM) relies on expressing the pedigree likelihood as a product of conditional probabilities, one for each individual. In addition to logistic regression modelling of measured epidemiological variables on disease prevalence, there is modelling of vertical transmission, of transmission of unmeasured genotypes and of sibship environment. This paper discusses methods for the analysis of binary traits in twins and in pedigrees. Some extensions to the RLM for pedigrees which include twins are proposed. These enable exploration of twin concordance in the context of the twins' common parenthood, the sibship similarities within the family, and the twins' similarity in age, sex, genes and environment.

Asthma↗