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Biomedical subjects

N G Martin

Publications and source records attributed to N G Martin.

At least 127 records · Page 7Linked to original sources
PubMed1998

Interaction of marital status and genetic risk for symptoms of depression.

Depression scores (DSSI) were available for 1232 MZ and 751 DZ female twin pairs who completed a mailed questionnaire. Pairs were divided into those concordant for being in a marriage-like state, concordant for having no partners, and those discordant. The pattern of twin correlations differed according to marital status. Our results suggest that having a marriage-like relationship acts as a protective factor in reducing the impact of inherited liability to symptoms of depression in the general population.

Adolescent↗
PubMed1998

Sex differences and non-additivity in the effects of genes on personality.

New large-sample data show that non-additive genetic effects, probably epistatic interactions between loci, and sex-limited gene expression are significant features of the genetic architecture of human personality as measured by questionnaire scales of extraversion and neuroticism. Three large data sets--new data on large samples (n = 20,554) of US twins, their spouses, parents, siblings and children, correlations for Australian twins (n = 7,532), and previously published twin data from Finland (n = 14,288)--are subjected to an integrated analysis to test alternative hypotheses about the genetic causes of family resemblance in personality. When allowance is made for differences in reliability of the scales, the combined data are consistent with the same model for variation. There are significant amounts of genetic non-additivity for both dimensions of personality. The evidence favours additive x additive epistatic interactions rather than dominance. In the case of neuroticism, there is especially strong evidence of sex differences in genetic architecture favouring a greater relative contribution of non-additive genetic effects in males. The data confirm previous claims to find no major contribution of the shared environment of twins and siblings to these dimensions of personality. Correlations between spouses are zero, and the correlations for very large samples of siblings and non-identical twins do not differ significantly.

Diseases in Twins↗
PubMed1998

A factor analysis of associations among self-reported immune related symptoms in a large twin sample.

We examined the cumulative prevalences of 22 symptoms thought to reflect immune system function reported in a questionnaire mailed to 7616 Australian twins. The associations between symptoms and demographic variables were expressed in terms of polychoric or polyserial correlations, and a principal components analysis performed. Factors representing underlying propensities respectively to allergic disease, various minor infections, diseases associated with aging such as arthritis, skin disease, and respiratory tract infection were extracted. Possible processes underlying these symptom clusters and the relative strengths and weaknesses of this type of analysis are discussed.

Adult↗
PubMed1998

Molecular biology of alcohol dependence, a complex polygenic disorder.

Alcohol dependence, and the medical conditions which arise from prolonged excessive alcohol use, have no single cause. Like other complex diseases, they result from a combination of social, personal and genetic contributions; but within any society genetic variation has a substantial influence on individual risk. The genes presently known to affect alcohol dependence produce variation in alcohol metabolism; other genes which affect personality or susceptibility to intoxication are likely to be significant but so far reproducible evidence is scanty. Designs which include related subjects have advantages for the study of complex diseases, because any association effects can be placed in the context of overall heritability and because linkage analysis can also be included. Examples of our studies of alcohol metabolism, consumption and dependence are presented.

Adult↗
PubMed1998

ADH genotypes and alcohol use and dependence in Europeans.

We have tested for effects of alcohol dehydrogenase (ADH) genotypes on self-reported alcohol consumption and symptoms of alcohol dependence, recorded on three occasions up to 15 years apart, in 377 male and female subjects of European descent. ADH2 genotype had significant effects on both consumption and dependence in the men, but not in the women. The effects of ADH3 genotype were considerably less than those of ADH2, but significant results could be demonstrated when the combined genotypes were considered. The direction of the effects on alcohol consumption and dependence risk were consistent with reports on Asian subjects, and with the in vitro properties of ADH isoenzymes. As with previous studies on the relationship between ADH type and alcohol use, population stratification cannot be excluded as a contributing factor in these results.

Adolescent↗
PubMed1998

Predictive factors of age at menopause in a large Australian twin study.

Various studies have investigated potential predictors of age at natural menopause but have produced inconsistent results. The relationship between age at natural menopause and socioeconomic, reproductive, and health behavioral factors was evaluated using longitudinal data from 5961 Australian female twins, aged 17 to 88 years at the time of study. The sample consisted of women voluntarily enrolled in the Australian Twin Registry. Failure-time analysis was the principal statistical method used to handle censored observations. Kaplan-Meier estimates showed the overall median age at natural menopause to be 51 years (95% confidence interval, 50-51). Median age at menopause was earlier for women with earlier birth year, women with late age of menarche, women who had no children, or women who were smokers. Differences in age at menopause between social, occupational, and educational groups were statistically significant (Mantel-Cox test, p < 0.001) for education, major occupational classification, combined income, and self-rated social class, with higher age at menopause for higher levels of each variable. A Cox proportional hazards model was used to estimate the odds ratio of the occurrence of natural menopause among different sub-groups, adjusted to reflect simultaneous effects of all other significant covariates. This large study provided clear trends of association in predictors relating to age at menopause. These trends may help to resolve uncertainties and conflicting results identified in studies of comparable white samples. The nature of the twin data also sets a solid background for future analyses of genetic and environmental variance components using statistical modeling or related methods.

Adolescent↗
PubMed1998

Smoking, obesity, and hypertension alter the dose-response curve and test sensitivity of carbohydrate-deficient transferrin as a marker of alcohol intake.

Serum carbohydrate-deficient transferrin (CDT) is a specific and comparatively sensitive marker of excessive alcohol use; however, reports of its sensitivity vary according to the population or patient groups studied and their average alcohol intake. We have characterized the dose-response curve between alcohol intake and CDT concentrations in a study of 1400 men and women from a community-based twin registry. Our results show that mean CDT increases with increasing reported alcohol consumption even within the range of alcohol use considered to be nonhazardous. We found significant effects of sex, age, smoking, previous alcohol dependence, body mass index, and diastolic hypertension on the alcohol-CDT dose-response curve. These variables either affect test sensitivity or require adjustment of reference intervals. The results also provide insight into the physiological and biochemical factors that affect CDT concentration.

Adult↗
PubMed1997

Characteristics of interview refusers: women who decline to participate in interviews relating to eating.

OBJECTIVES: The aim of this study was to compare the eating habits and weight ranges of 27 women who refused to participate in a semistructured interview on eating with 25 women who agreed to participate, to determine if there were any systematic differences between the two groups. METHOD: The women had previously completed a general psychiatric interview that also included a lifetime DSM-III-R diagnosis of eating disorders. About 2 years after this interview, the women were asked to participate in an interview that would specifically examine eating behaviors. RESULTS: In contrast to the results of previous studies, this study found that there was no difference between women who refused or agreed to participate in an interview about eating, in terms of their eating problems or weight ranges. CONCLUSIONS: It seems that eating or weight problems need not be overrepresented in groups who refuse to participate in surveys about eating, thereby undermining the accuracy of prevalence rates in the general population. Suggestions for achieving this representation are discussed.

Adult↗
PubMed1997

Genetic factors in the aetiology of mouth ulcers.

The aetiology of mouth ulcers is uncertain, and prior research has indicated both environmental and genetic factors. In this study, information on mouth ulcer incidence was collected for 290 twin pairs--127 monozygous (MZ) and 163 dizygous (DZ)--and their parents, a total of 1,160 people. Self-reported data on mouth ulcer incidence were available for the twins, and in each family the mother also reported on the mouth ulcer incidence in the twins, the twins' father, and herself. A structural equation model--combining a measurement model, a rater bias model, and a model including genetic and environmental influences--was used to explain variation in mouth ulcers. The fitted model explained the variation in a latent phenotype of mouth ulcer incidence for the twins in terms of an additive genetic factor (64%), a common environment factor (26%), and a specific environment factor (10%). The mothers' ratings showed a significant positive bias.

Bias↗
PubMed1997

The consistency of recalled age at first sexual intercourse.

It is widely believed that people can remember the age at which they first had sexual intercourse. Questions about age at onset are routinely asked in population sexual behaviour surveys and in clinical history-taking. However, there are limited test-retest data, especially with regard to individual differences in unreliable recall. In this study, telephone interviews and follow-ups an average of 15 months later were conducted with 570 non-virgin subjects aged between 28 and 73 years. Test-retest correlations for recalled age at first intercourse were 0.85 for females and 0.91 for males. Consistency was slightly lower among older people and women with a history of sexual abuse. There were no significant associations between consistency of recall and measures of personality, educational background or history of alcohol dependence and depression.

Adult↗
PubMed1997

Genetic and environmental contributions to alcohol dependence risk in a national twin sample: consistency of findings in women and men.

BACKGROUND: Genetic influences on alcoholism risk are well-documented in men, but uncertain in women. We tested for gender differences in genetic influences on, and risk-factors for, DSM-III-R alcohol dependence (AD). METHOD: Diagnostic follow-up interviews were conducted in 1992-3 by telephone with twins from an Australian twin panel first surveyed in 1980-82 (N = 5889 respondents). Data were analysed using logistic regression models. RESULTS: Significantly higher twin pair concordances were observed in MZ compared to DZ same-sex twin pairs in women and men, even when data were weighted to adjust for over-representation of well-educated respondents, and for selective attrition. AD risk was increased in younger birth cohorts, in Catholic males or women reporting no religious affiliation, in those reporting a history of conduct disorder or major depression and in those with high Neuroticism, Social Non-conformity, Toughmindedness, Novelty-Seeking or (in women only) Extraversion scores; and decreased in 'Other Protestants', weekly church attenders, and university-educated males. Controlling for these variables, however, did not remove the significant association with having an alcoholic MZ co-twin, implying that much of the genetic influence on AD risk remained unexplained. No significant gender difference in the genetic variance in AD was found (64% heritability, 95% confidence interval 32-73%). CONCLUSIONS: Genetic risk-factors play as important a role in determining AD risk in women as in men. With the exception of certain sociocultural variables such as religious affiliation, the same personality, sociodemographic and axis I correlates of alcoholism risk are observed in women and men.

Adult↗
PubMed1997

Modeling genetic and environmental influences in the etiology of conduct disorder: a study of 2,682 adult twin pairs.

The etiology of conduct disorder (CD) was examined retrospectively in a sample of 2,682 male, female, and unlike-sex adult twin pairs from the community-based Australian Twin Register. Model-fitting analyses indicated a substantial genetic influence on risk for CD, accounting for 71% of the variance (95% confidence interval [CI] = 32-79%). There was not a statistically significant effect of the shared environment in the best-fitting model of CD, but a modest effect of the shared environment on the risk for CD could not be rejected (95% CI = 0-32%). The magnitude of genetic and environmental influences for CD liability did not vary significantly for boys and girls, and the specific genetic and environmental mechanisms important for the development of CD appeared to be largely the same for both sexes. The fit of a multiple-threshold model raises the possibility that CD may not necessarily be a discrete entity but rather an extreme of the normal variation in conduct-disordered behavior found in the general population.

Adult↗
PubMed1997

Characterization of melanocyte stimulating hormone receptor variant alleles in twins with red hair.

The association between MSHR coding region variation and hair colour in humans has been examined by genotyping 25 red haired and 62 non-red Caucasians, all of whom were 12 years of age and members of a twin pair study. Twelve amino acid substitutions were seen at 11 different sites, nine of these being newly described MSHR variants. The previously reported Val92Met allele shows no association with hair colour, but the three alleles Arg151Cys, Arg160Trp and Asp294His were associated with red hair and one Val60Leu variant was most frequent in fair/blonde and light brown hair colours. Variant MSHR genotypes are associated with lighter skin types and red hair (P < 0.001). However, comparison of the MSHR genotypes in dizygotic twin pairs discordant for red hair colour indicates that the MSHR gene cannot be solely responsible for the red hair phenotype, since five of 13 pairs tested had both haplotypes identical by state (with three of the five having both identical by descent). Rather, it is likely that additional modifier genes exist, making variance in the MSHR gene necessary but not always sufficient, for red hair production.

Alleles↗
PubMed1997

Participation bias in a sexuality survey: psychological and behavioural characteristics of responders and non-responders.

BACKGROUND: Few studies of sexual attitudes and behaviour have quantified the direction and magnitude of participation bias, primarily because information on non-responders is difficult to obtain in cross-sectional surveys. METHOD: Australian adult twins (n = 9112) aged 17-52 years enrolled in a national, longitudinal research register were asked to participate in a postal survey concerning their sexual behaviour and attitudes. Individual consent was determined by separate return of a consent form; 27% explicitly refused, 19% initially agreed to receive a questionnaire, but subsequently did not return consent forms and 52% explicitly consented. Participation data were matched to social, psychological and behavioural information in a longitudinal data set. RESULTS: People who explicitly consented had higher levels of education, attended church less often, had less conservative sexual attitudes and voting preferences, were more likely to smoke cigarettes and drank alcohol more often than people who explicitly refused. On standard personality scales, responders were more novelty-seeking and reward-dependent and less harm-avoidant than refusers. Structured psychiatric telephone interview data from 3674 individuals showed that, compared to refusers, responders had higher lifetime prevalence of major depression, alcohol dependence and childhood conduct disorder and also reported an earlier age at first sexual intercourse and higher rates of sexual abuse. In general, those who had initially agreed to receive the sex questionnaire but were subsequently lost were more similar to consenters than to refusers. CONCLUSIONS: Effect sizes on most measures were small. The broad profile suggests that postal surveys of sexual attitudes and behaviour may overestimate sexual liberalism, activity and adversity, although this bias should not seriously compromise population estimates.

Adolescent↗
PubMed1997

MN blood group affects response of serum LDL cholesterol level to a low fat diet.

Previous studies found that MZ twin pairs who are blood group NN have greater intrapair variability in plasma lipid levels than those who are MM or MN. This led to the prediction that the response of plasma lipid levels to a low fat diet would depend on MN blood group, the greatest response being in those who are NN. The present study was based upon 254 patients who took part in the Australian Polyp Prevention Project. This was a 2 x 2 x 2 randomised factorial design based upon the presence or absence of the three factors: a dietary fibre supplement, a beta-carotene supplement and reduced intake of dietary fat. The lowering of plasma, low density lipoprotein (LDL) cholesterol, in response to a low fat diet was greatest in those who were NN and least in MN heterozygotes. Overall, a reduction in LDL level was observed in the 47% of the APPP population who were on a low fat diet and who were homozygous MM or NN. The result was consistent with a balanced polymorphism at or near the GLYA locus on chromosome 4 that influences the sensitivity of plasma lipid levels to dietary fluctuations in fat intake.

Cholesterol, LDL↗
PubMed1997

Genetic effects on variation in red-blood-cell folate in adults: implications for the familial aggregation of neural tube defects.

Recent studies have implicated folic acid as an important determinant of normal human growth, development, and function. Insufficient folate levels appear to be a risk factor for neural tube defects (NTD), as well as for several chronic diseases of adulthood. However, relatively little is known about the factors that influence folate status in the general population. To estimate the relative contribution of genetic and nongenetic factors to variation in folate, we have evaluated red blood cell (RBC) folate levels in 440 pairs of MZ twins and in 331 pairs of DZ twins. The data were best described by a model in which 46% of the variance in RBC folate was attributable to additive genetic effects, 16% of the variance was due to measured phenotypic covariates, and 38% of the variance was due to random environmental effects. Moreover, the correlations for RBC folate in MZ co-twins (r = .46) and in repeat measures from the same individual (r = .51) were very similar, indicating that virtually all repeatable variation in RBC folate is attributable to genetic factors. On the basis of these results, it would seem reasonable to initiate a search for the specific genes that influence RBC folate levels in the general population. Such genes ultimately may be used to identify individuals at increased risk for NTD and other folate-related diseases.

Adult↗