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Biomedical subjects

N G Martin

Publications and source records attributed to N G Martin.

At least 109 records · Page 6Linked to original sources
PubMed1999

Religious attendance and frequency of alcohol use: same genes or same environments: a bivariate extended twin kinship model.

Religious attendance has been shown to correlate negatively with alcohol use. We investigated whether this relationship is driven by genetic or environmental factors. Data on frequency of church attendance and frequency of alcohol use were obtained from twins and their families in the Virginia 30,000 study. A comprehensive bivariate model of family resemblance was fitted to the data using Mx. This model is described in detail. Results indicate that genetic factors primarily account for the relationship between alcohol and church attendance in males, whilst shared environmental factors, including cultural transmission and genotype-environment covariance, are stronger determinants of this association in females.

Alcohol Drinking↗
PubMed1999

Genetics of early cancer detection behaviours in Australian female twins.

Early detection of cervical and breast cancers is an important component of women's health strategy. Screening programmes, health professional interventions and preventive behaviours such as breast self-examination provide the means to this end. Our twin study sought to identify the relative influence of environmental and genetic factors on liability to early cancer detection behaviours, including use of cervical smear tests, mammograms, and breast examination. Additive genetic and random environmental effects models gave the best, most parsimonious fit to the data for each early cancer detection behaviour. The heritability of liability to Pap smear use was 66%, mammogram use 50%, breast examination by a doctor or nurse 38% and breast self-examination 37%. Genetic influences were behaviour-specific; there was no evidence for a common genetic influence on the four behaviours. Potential covariates investigated included age, amount of contact between co-twins, educational level and personality traits such as harm avoidance, novelty seeking, reward dependence, neuroticism, anxiety, depression, self-esteem, perceived control, interpersonal dependency and ways of coping. None were significant. The study was carried out before the implementation of national screening programmes with media campaigns to increase participation rates. Hence follow-up investigation, including data on regularity of behaviours, would be informative.

Adaptation, Psychological↗
PubMed1999

Some implications of chaos theory for the genetic analysis of human development and variation.

Non-linear epigenetic processes are a potential underlying source of phenotypic differences in development. Simulation studies of twin pairs using simple non-linear development models characterised by chaotic or near-chaotic behavior are presented. The effect of chaotic processes on correlations is to lower them from their initial values, but high initial correlations are affected much less by chaotic and near-chaotic processes than intermediate correlations. Therefore, we would predict that traits affected by chaotic processes would have high MZ and low DZ twin correlations and this is reminiscent of certain traits such as EEG spectra. However the much more frequent observation of MZ correlations close to twice their DZ counterparts would suggest that the role of chaos in development is quite limited.

Computer Simulation↗
PubMed1999

Mendelian segregation of normal CAG trinucleotide repeat alleles at three autosomal loci.

Segregation ratio distortion (SRD) with preferential transmission of expanded CAG alleles has been reported in Machado-Joseph disease (MJD/SCA3), spinocerebellar ataxia type I (SCA1), and dentatorubral-pallidoluysian atrophy (DRPLA). We have examined the transmission frequencies of alleles in normal heterozygotes at these disease loci in 377 pairs of twins and their parents and find no evidence for SRD.

Adolescent↗
PubMed1998

Testing a genetic structure of blood-injury-injection fears.

Multivariate genetic analyses were used to examine the genetic and environmental contributions to individual differences in fears of blood, injury, and injections in 659 twin pairs who completed questions concerning fear and fainting around blood, injury, and injections, and fainting in situations not involving blood, as well as the personality scales of Neuroticism, and Harm Avoidance. There was significant familial aggregation of blood fears but univariate analyses were unable to distinguish between additive genetic or shared environmental variables, or both, as the cause. The same was true of blood fainting. Non-blood-injury fainting was best explained by a model assuming shared and unique environmental variables. However, multivariate genetic analyses, which capitalise on extra information contained by all the covariance terms, indicated that the variance in blood-injury-injection fear was principally attributable to unique environmental events specific to this fear and additive genetic factors shared with fainting. The data are discussed in the context of models of blood-injury phobia that identify the need to consider separate etiological mechanisms for fear and fainting.

Female↗
PubMed1998

Segregation analysis of cutaneous melanoma in Queensland.

To investigate whether the familial clustering of cutaneous melanoma is consistent with Mendelian inheritance of a major autosomal gene, maximum likelihood segregation analyses were performed in a population-based sample of 1,912 families ascertained through a proband with melanoma diagnosed in Queensland between 1982 and 1990. Analyses were performed with the S.A.G.E. statistical package, using the REGTL program for a binary trait with a variable age of onset. We sought medical confirmation for all family members reported to have had melanoma, and only medically verified cases among relatives were included in the analyses. The hypothesis of codominant Mendelian inheritance gave a significantly better fit to the data than either dominant or recessive Mendelian inheritance, or environmental transmission. Overall, both Mendelian inheritance of a single major gene, and purely environmental transmission were rejected (P < 0.001). In both the single major gene and environmental models, there was strong evidence of familial dependence in melanoma occurrence (P < 0.001). These results are consistent with reported genetic heterogeneity in melanoma inheritance and suggest that other familial factors, such as pigmentation, skin type, and sun exposure habits, may play an important role in the familial clustering of melanoma.

Adult↗
PubMed1998

Complete sequence and polymorphism study of the human TYRP1 gene encoding tyrosinase-related protein 1.

The complete 24,667 nucleotide sequence spanning the human TYRP1 gene has been determined from the inserts of two overlapping lambda clones. A LINE-1 repeat element is immediately adjacent to and may demarcate the immediate 5' promoter region of the gene. A search for polymorphism within the seven TYRP1 coding exons has been performed by an RNase mismatch detection procedure. Analysis of the TYRP1 gene in 100 Caucasian individuals of varying hair color has found no amino acid sequence variation nor revealed any hemizygous mutant allele in the hypopigmented phenotype of two 9p- syndrome patients.

Base Sequence↗
PubMed1998

Suicidal behaviour: an epidemiological and genetic study.

BACKGROUND: Psychiatric history, familial history of suicide attempts, and certain traumatic life events are important predictors of suicidal thoughts and behaviour. We examined the epidemiology and genetics of suicidality (i.e. reporting persistent suicidal thoughts or a plan or suicide attempt) in a large community-based sample of MZ and DZ twin pairs. METHOD: Diagnostic telephone interviews were conducted in 1992-3 with twins from an Australian twin panel first surveyed in 1980-82 (N = 5995 respondents). Data were analysed using logistic regression models, taking into account twin pair zygosity and the history of suicidality in the respondent's co-twin. RESULTS: Lifetime prevalence of suicidal thoughts and attempts was remarkably constant across birth cohorts 1930-1964, and across gender. Major psychiatric correlates were history of major depression, panic disorder, social phobia in women, alcohol dependence and childhood conduct problems. Traumatic events involving assault (childhood sexual abuse, rape or physical assault) or status-loss (job loss, loss of property or home, divorce), and the personality trait neuroticism, were also significantly associated with suicide measures. Prevalence of serious suicide attempts varied as a function of religious affiliation. After controlling for these variables, however, history of suicide attempts or persistent thoughts in the respondent's co-twin remained a powerful predictor in MZ pairs (odds ratio = 3.9), but was not consistently predictive in DZ pairs. Overall, genetic factors accounted for approximately 45% of the variance in suicidal thoughts and behaviour (95% confidence interval 33-51%). CONCLUSIONS: Risk of persistent suicidal thoughts and suicide attempts is determined by a complex interplay of psychiatric history, neuroticism, traumatic life experiences, genetic vulnerability specific for suicidal behaviour and sociocultural risk or protective factors.

Adult↗
PubMed1998

Genetic and environmental risk factors for the weight and shape concerns characteristic of bulimia nervosa.

BACKGROUND: This study seeks to identify the genetic and environmental risk factors for the overvalued ideas that are characteristic of bulimia nervosa, using a biometrical model fitting approach with twin data. METHODS: The Eating Disorder Examination (EDE), which can be used to gain continuous measures of dietary restraint, eating concern, weight concern and shape concern, was administered to 325 female twins, both monozygotic (MZ) and dizygotic (DZ). For each subscale, questions were asked concerning the month prior to interview and lifetime prevalence ('ever'). RESULTS: Model fitting indicated that there is a powerful role of the environment in shaping women's attitude towards weight, shape, eating and food, ranging from 38% to 100% of the variance. For all subscales, with the exception of weight concern, the best explanation for individual variation was one that incorporated additive genetic and non-shared environmental influences. In contrast, model fitting indicated that non-shared and shared environmental influences best explained the variance of weight concern. CONCLUSIONS: With the exception of the Shape Concern subscale, environmental factors make a greater contribution than genetic factors to the development of the overvalued ideas that are seen to be one of the triggers for the development of bulimia nervosa. Given this substantial role of the environment influences, it seems likely that environmental manipulation can be effective in the prevention of bulimia nervosa.

Body Constitution↗
PubMed1998

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.

Adolescent↗
PubMed1998

A comparison of adult female twins from opposite-sex and same-sex pairs on variables related to reproduction.

In several litter-bearing species, prenatal exposure of a female fetus to hormones from adjacent male fetuses can lead to later effects on various anatomical and behavioral characteristics of the female, including a number related to reproduction. To see if such traits are also affected in humans, adult female twins from a large Australian sample who had male cotwins were compared to females with female cotwins on 90 questionnaire items related to reproductive functions. No substantial effects could be clearly demonstrated, although some weak effects remained a possibility. Some variables, such as age at first menstruation, age at first pregnancy, and height, were consistent in direction with results from the animal literature, although the effect sizes were small and not statistically significant.

Adult↗
PubMed1998

Assessing the effects of cooperation bias and attrition in behavioral genetic research using data-weighting.

Because twins and adoptees are a rare resource, they are often studied repeatedly over a period of many years. Differential attrition, and in some studies initial cooperation bias, have the potential to lead to serious biases to estimates of genetic and environmental parameters. Since non-response is often influenced by multiple binary or categorical sociodemographic variables, maximum-likelihood methods are not easily adapted to adjust for such effects. In this brief note we illustrate the use of data-weighting to assess the likely effects of cooperation bias or attrition both on measures of mean or prevalence, and on twin pair correlations or concordances, using data from the Australian twin panel 1981 survey and alcohol challenge studies. Participants in the alcohol challenge study were on average younger, more socially nonconforming, heavier drinkers, more likely to be unmarried, and less likely to report their religion as Other Protestant. Reweighting the alcohol challenge sample to have the same distribution on these variables as the Australian twin panel 1981 survey respondents confirmed that individuals who would feel very intoxicated after a challenge dose of alcohol were underrepresented in the study. However, pairwise data-weighting indicated that this cooperation bias was leading to only a slight underestimation of the importance of genetic effects on subjective intoxication.

Adoption↗
PubMed1998

Common genetic risk factors for conduct disorder and alcohol dependence.

The association between retrospectively reported childhood conduct disorder (CD) and a history of alcohol dependence (AD) was examined in a sample of 2,682 male, female, and unlike-sex adult twin pairs. There was a strong association between CD and AD in both men (tetrachoric r = .34, odds ratio = 2.8) and women (tetrachoric r = .53, odds ratio = 9.9). Genetic factors accounted for most of the association between CD and AD liability in men and women, with the remainder of the association being due to nonshared individual-specific environmental factors. Genetic influences common to CD and AD accounted for 17% and 35% of the genetic variation in AD liability in men and women, respectively, and accounted for 11% and 23% of the total variation in AD liability in men and women, respectively. The results suggest that there are common genetic risk factors for CD and AD or that CD itself is an important genetically influenced risk factor for AD.

Adult↗
PubMed1998

Genetic and environmental risk factors for asthma: a cotwin-control study.

In complex diseases of genetic etiology such as asthma and atopy, it is difficult to differentiate causes of disease from consequences, and quantitate the importance of such causative factors. We examined possible risk factors for the development of wheezing and bronchial hyperresponsiveness in a cotwin-control study nested within a larger community-based twin-family study. In 62 monozygotic (MZ) twin pairs discordant for a history of wheezing, skin prick test to house dust extract was the most important discriminator, followed by sensitization to cat and cockroach allergens. In contrast, 62 dizygotic (DZ) discordant twin pairs differed additionally in sensitization to grass pollens and fungi. Markers such as serum haptoglobin, serum magnesium, and alpha-1-antitrypsin levels did not differ significantly between discordant twins. This MZ/DZ difference suggests that pollen allergy in asthmatics is more an epiphenomenon due to a genetic correlation between asthma and the allergic diathesis, whereas indoor allergens are likely to be direct environmental causes of asthma.

Adult↗
PubMed1998

Statistical methods in genetic research on smoking.

A growing body of evidence suggests that genetic factors have an important influence on the onset and course of smoking. Here we review some of the statistical methods that have been used to test for genetic influences on smoking behaviour, with a particular focus on studies of large national twin samples. We show how many of the hypotheses that have been tested using a genetic model-fitting approach have also been reformulated using logistic regression models that will be more familiar to epidemiologists. Such an approach is more easily extended to allow for sociocultural, as well as genetic, influences on smoking behaviour. Using either approach, data are consistent in indicating that certainly in men, and possibly in women, genetic factors play an important role in predicting which individuals who become cigarette smokers progress to being long-term persistent smokers.

Epidemiologic Methods↗
PubMed1998

Effects of lifestyle, personality, symptoms of anxiety and depression, and genetic predisposition on subjective sleep disturbance and sleep pattern.

The effects on sleep pattern ('short-sleep' versus 'long-sleep') and subjective sleep disturbance of genotype, personality, symptoms of anxiety and depression, and lifestyle, were examined using survey data on a clinically unselected sample of adult Australian twin pairs, aged 17-88 years. When the effects of genotype, personality and symptoms were ignored, lifestyle variables appeared to account for roughly 4% of the variance in sleep disturbance, and 9% of the variance in sleep pattern. Significant genetic effects on sleep disturbance and sleep pattern were found, which were only partly explained by the effects of personality and symptoms of anxiety and depression. Much of the association between sleep disturbance and lifestyle appeared to be explained by separate effects of personality and symptoms of anxiety and depression on sleep and lifestyle ('genotype-risk-factor correlation'). There was little evidence for genetically determined differences in sensitivity to the lifestyle variables ('genotype x risk-factor interaction').

Adolescent↗