15 results on '"N. G. Martin"'
Search Results
2. Genetic influence on ERP slow wave measures of working memory
- Author
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N K, Hansell, M J, Wright, G M, Geffen, L B, Geffen, G A, Smith, and N G, Martin
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Cerebral Cortex ,Male ,Adolescent ,Models, Genetic ,Intelligence ,Individuality ,Twins ,Genetic Variation ,Prefrontal Cortex ,Retention, Psychology ,Electroencephalography ,Social Environment ,Parietal Lobe ,Humans ,Female - Abstract
Individual differences in the variance of event-related potential (ERP) slow wave (SW) measures were examined. SW was recorded at prefrontal and parietal sites during memory and sensory trials of a delayed-response task in 391 adolescent twin pairs. Familial resemblance was identified and there was a strong suggestion of genetic influence. A common genetic factor influencing memory and sensory SW was identified at the prefrontal site (accounting for an estimated 35%-37% of the reliable variance) and at the parietal site (51%-52% of the reliable variance). Remaining reliable variance was influenced by unique environmental factors. Measurement error accounted for 24% to 30% of the total variance of each variable. The results show genetic independence for recording site, but not trial type, and suggest that the genetic factors identified relate more directly to brain structures, as defined by the cognitive functions they support, than to the cognitive networks that link them.
- Published
- 2002
3. Genetic influence on the variance in P3 amplitude and latency
- Author
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M J, Wright, N K, Hansell, G M, Geffen, L B, Geffen, G A, Smith, and N G, Martin
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Cerebral Cortex ,Male ,Adolescent ,Intelligence ,Twins ,Genetic Variation ,Electroencephalography ,Event-Related Potentials, P300 ,Parietal Lobe ,Mental Recall ,Reaction Time ,Humans ,Attention ,Female - Abstract
The P3(00) event-related potential (ERP) component is widely used as a measure of cognitive functioning and provides a sensitive electrophysiological index of the attentional and working memory demands of a task. This study investigated what proportion of the variance in the amplitude and latency of the P3, elicited in a delayed response working memory task, could be attributed to genetic factors. In 335 adolescent twin pairs and 48 siblings, the amplitude and latency of the P3 were examined at frontal, central, and parietal sites. Additive genetic factors accounted for 48% to 61% of the variance in P3 amplitude. Approximately one-third of the genetic variation at frontal sites was mediated by a common genetic factor that also influenced the genetic variation at parietal and central sites. Familial resemblance in P3 latency was due to genetic influence that accounted for 44% to 50% of the variance. Genetic covariance in P3 latency across sites was substantial, with a large part of the variance found at parietal, central, and frontal sites attributed to a common genetic factor. The findings provide further evidence that the P3 is a promising phenotype of neural activity of the brain and has the potential to be used in linkage and association analysis in the search for quantitative trait loci (QTLs) influencing cognition.
- Published
- 2002
4. A study of the genetic and environmental etiology of stuttering in a selected twin sample
- Author
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S, Felsenfeld, K M, Kirk, G, Zhu, D J, Statham, M C, Neale, and N G, Martin
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Adult ,Cohort Studies ,Male ,Adolescent ,Risk Factors ,Diseases in Twins ,Twins, Dizygotic ,Humans ,Female ,Genetic Predisposition to Disease ,Stuttering ,Twins, Monozygotic ,Social Environment - Abstract
Stuttering is a developmental disorder of speech production that usually emerges in childhood. In this study, a large population-based twin sample from the Australian Twin Registry (1567 pairs and 634 singles aged 17-29 years) was screened to identify twin pairs in which one or both members reported themselves to be affected by stuttering. Telephone interview-based diagnoses were obtained for 457 of these individuals (self-reported affected cases, cotwins, and controls) to determine whether the self-report was correct. To correct for ascertainment bias we carried out a bivariate analysis of the final diagnosis in the selected sample with the screening item in the full sample, using the categorical raw data option of Mx 1.47c. After correcting for ascertainment bias, approximately 70% (95% confidence interval: 39-86%) of the variance in liability to stuttering was found to be attributable to additive genetic effects, with the remainder due to nonshared environmental effects.
- Published
- 2001
5. Measurement models for sexual orientation in a community twin sample
- Author
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K M, Kirk, J M, Bailey, M P, Dunne, and N G, Martin
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Adult ,Male ,Adolescent ,Models, Genetic ,Sexual Behavior ,Homosexuality ,Twins, Monozygotic ,Middle Aged ,Social Environment ,Cohort Studies ,Phenotype ,Twins, Dizygotic ,Humans ,Female - Abstract
Multivariate structural equation modeling techniques have been applied to examine the causes of individual differences in responses to several items concerning sexual orientation. To minimize potential ascertainment and response biases, the study sample involved a large (N = 4901) community-based cohort of Australian twins aged 18-52 who answered an anonymous questionnaire on sexual behavior and attitudes. The statistical power of the analysis was increased by the availability of multiple measures of sexual orientation (behaviors, attitudes and feelings), providing stronger evidence for the existence of additive genetic influences on this phenotype than in a previous analysis (Bailey et al., 2000). Estimates of the heritability of homosexuality in this sample ranged between 50 and 60% in females but were significantly lower (heritability of approximately 30%) in males.
- Published
- 2001
6. Further evidence against the environmental transmission of individual differences in neuroticism from a collaborative study of 45,850 twins and relatives on two continents
- Author
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R I, Lake, L J, Eaves, H H, Maes, A C, Heath, and N G, Martin
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Adult ,Male ,Adolescent ,Models, Genetic ,Neurotic Disorders ,Australia ,Individuality ,Middle Aged ,Social Environment ,United States ,Diseases in Twins ,Humans ,Female ,Aged - Abstract
We examine the hypothesis that environmental transmission is a significant factor in individual differences for Neuroticism among 45,850 members of extended twin kinships from Australia (N = 20,945) and the United States (N = 24,905). To this large data set we fitted a model estimating genetic and environmental components of variance and gene-environmental covariance to examine the causes of individual differences in Neuroticism. For the combined sample we reject models including environmental transmission, shared environment, and a special twin environment in favor of more parsimonious genetic models. The best-fitting model involved only modest assortative mating, nonshared environment, and both additive and nonadditive genetic components. We conclude, first, that there is no evidence for environmental transmission as a contribution to individual differences in Neuroticism in these replicated samples, drawn from different continents, and, second, that a simple genetic structure underlies familial resemblance for the personality trait of Neuroticism. It is interesting that, despite the opportunity provided by the elaborate design and extensive power of our study, the picture revealed for the causes of individual differences in Neuroticism is little more complex than that found from earlier, simpler designs applied to smaller samples. However, this simplicity could not have been confirmed without using a highly informative design and a very large sample.
- Published
- 2000
7. Dimensions of psychological masculinity-femininity in adult twins from opposite-sex and same-sex pairs
- Author
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J C, Loehlin and N G, Martin
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Adult ,Male ,Sex Differentiation ,Pregnancy ,Prenatal Exposure Delayed Effects ,Twins, Dizygotic ,Gender Identity ,Humans ,Female ,Twins, Monozygotic ,Middle Aged ,Gonadal Steroid Hormones - Abstract
Male and female twins with opposite-sex co-twins were compared to twins with same-sex co-twins on three independent dimensions of masculinity-femininity, in order to examine the hypothesis that the hormones of the co-twin might have an effect on prenatal masculinization. The analysis was originally carried out for an older cohort from the Australian Twin Registry (2647 pairs, mean age 41.2), and then repeated in a younger cohort (1503 pairs, mean age 23.2). For women, the results on two of the three scales support and extend that of an earlier large study in Finland by Rose et al. (1994), who found no effect of sex of co-twin on feminine interests. One of the two scales contrasted worried and calm individuals, the other, confiding and reserved ones. The third scale, willingness to break or bend rules, showed a small effect of shared environmental influence, and it lay in the expected direction for a prenatal hormonal effect--females with a male co-twin scored higher (more like males). Most previous studies have not looked at the effect of sex of co-twin on males. The present study detected several such effects, although all were small in magnitude. The pattern was complex: sometimes the effect was in the masculine direction, sometimes in the feminine direction; sometimes there was agreement between the older and younger cohorts, sometimes not. Overall, the results suggest that no simple masculinization hypothesis--prenatal or postnatal--will adequately account for all the evidence. Age, sex, and aspect of masculinity-femininity must be taken into account.
- Published
- 2000
8. The genetics of smoking persistence in men and women: a multicultural study
- Author
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P A, Madden, A C, Heath, N L, Pedersen, J, Kaprio, M J, Koskenvuo, and N G, Martin
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Adult ,Cross-Cultural Comparison ,Male ,Adolescent ,Risk Factors ,Smoking ,Diseases in Twins ,Humans ,Female ,Genetic Predisposition to Disease ,Middle Aged ,Social Environment - Abstract
Using a correlated liability dimensions model, we examined the extent to which the same genetic and environmental factors influence both initiation of regular cigarette smoking and maintenance of the smoking habit in men and women. We analyzed questionnaire survey data obtained from large samples of male and female like-sexed twins from three countries, Australia (N = 1535 pairs), Sweden (N = 5916 pairs), and Finland (N = 4438 pairs), subdivided into three age bands (18-25, 26-35, and 36-46 years of age). We found that familial influences on risk for persistence in smoking cannot be entirely explained by the same factors responsible for risk of smoking initiation. Total genetic variance for smoking persistence varied little by age band and sex (range, 39-49% in women and 42-45% in men); however, even among twins in the youngest group (18-25 years of age), who on average have the fewest years of cigarette use, less than 40% of the total genetic variance in smoking persistence was accounted for by the same genetic factors that increased risk of smoking initiation, and this percentage decreased to less than 10% in the 36-46 year olds.
- Published
- 2000
9. Genetic and social determinants of initiation and age at onset of smoking in Australian twins
- Author
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A C, Heath, K M, Kirk, J M, Meyer, and N G, Martin
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Adult ,Male ,Adolescent ,Smoking ,Age Factors ,Australia ,Diseases in Twins ,Humans ,Female ,Genetic Predisposition to Disease ,Social Environment - Abstract
Retrospective data on age at onset of smoking, reported by 3810 adult Australian twin pairs, were analyzed to determine the role of genetic and environmental factors in the onset of smoking. Results of nonmetric multidimensional scaling supported a two-process model in which different etiologic factors determined which individuals were at risk of becoming smokers and the age at onset of smoking in those who were at risk. Parametric model-fitting confirmed this difference. For female twins and younger male twins (aged 30 years or less), the onset of smoking was strongly influenced by genetic factors, with shared and nonshared environmental effects having a more modest impact. For older male twins, shared environmental influences on onset of smoking were very important, and the influence of genetic predisposition was slight. The age at which smoking onset occurred, however, was influenced by both genetic and nonshared environmental effects, but not by shared environmental effects, in both sexes and both cohorts.
- Published
- 2000
10. An assessment of the genetic relationship between alcohol metabolism and alcoholism risk in Australian twins of European ancestry
- Author
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J D, Grant, A C, Heath, P A, Madden, K K, Bucholz, J B, Whitfield, and N G, Martin
- Subjects
Adult ,Europe ,Male ,Alcoholism ,Ethanol ,Metabolic Clearance Rate ,Australia ,Diseases in Twins ,Ethnicity ,Humans ,Female ,Genetic Predisposition to Disease - Abstract
The present analyses examined genetic influences on alcohol metabolism and their possible relationship to risk of alcohol dependence. Subjects were 206 Australian twin pairs who participated in an alcohol challenge protocol in 1979-1981, in which they were given a 0.75 g/kg dose of alcohol; blood alcohol concentrations (BACs) measured at five times over a 3-hr period after alcohol ingestion were examined. Structural equation modeling, fitting a combined autoregressive and common factor model, indicated significant heritabilities for both men and women (h2 range = 0.19-0.71), with significant parameter heterogeneity as a function of gender. In 1992-1993, both twins from 159 of the alcohol challenge pairs completed a telephone-administered psychiatric diagnostic interview. Repeated-measures MANOVAs were used to examine whether respondent's or cotwin's DSM-III-R alcohol dependence status, or parental history of alcohol problems, was associated with variation in alcohol metabolism. There was some evidence that individuals at increased genetic risk of alcohol dependence [with either a paternal history of alcohol problems (women) or an MZ male cotwin who reported a history of alcohol dependence by 1992-1993] showed lower initial BACs than other groups. However, this effect was not seen in those who themselves had a history of alcohol dependence by interview follow-up, perhaps because this relationship was already masked by a history of excessive drinking at baseline.
- Published
- 2000
11. A genetic analysis of the eating and attitudes associated with bulimia nervosa: dealing with the problem of ascertainment in twin studies
- Author
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T, Wade, M C, Neale, R I, Lake, and N G, Martin
- Subjects
Adult ,Models, Genetic ,Patient Selection ,Statistics as Topic ,Australia ,Twins, Monozygotic ,Middle Aged ,Sampling Studies ,Self Concept ,Body Image ,Twins, Dizygotic ,Humans ,Female ,Longitudinal Studies ,Bulimia - Abstract
Little is known about the etiology of bulimia nervosa and the attitudes associated with it. We have undertaken a study of selected (45 pairs) and unselected (106 pairs) female twins to elucidate the broad causes of individual differences in these behaviours and attitudes. The selected sample was chosen on the basis of at least one of the twin pair having a lifetime incidence of bulimia nervosa. Biometrical model fitting, which corrected for the biased twin correlations of the ascertained group, was used to investigate the genetic and environmental risk factors contributing to the development of bulimia nervosa. The best-fitting model showed that individual variation was best explained by additive genetic influences (62%) and nonshared environmental influences (38%). The proportion of genetic variance affecting individual variation in the ascertained group and the random group was not found to be significantly different. In summary, it is suggested that it may not be necessary to supplement a randomly selected sample with an ascertained sample when investigating the liability to a low-prevalence psychiatric disorder if a continuous measure of that disorder is available.
- Published
- 1999
12. Longitudinal genetic analysis of menstrual flow, pain, and limitation in a sample of Australian twins
- Author
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S A, Treloar, N G, Martin, and A C, Heath
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Phenotype ,Adolescent ,Dysmenorrhea ,Models, Genetic ,Australia ,Diseases in Twins ,Twins, Dizygotic ,Humans ,Female ,Twins, Monozygotic ,Menorrhagia - Abstract
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.
- Published
- 1998
13. A comparison of adult female twins from opposite-sex and same-sex pairs on variables related to reproduction
- Author
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J C, Loehlin and N G, Martin
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Adult ,Male ,Analysis of Variance ,Logistic Models ,Sex Factors ,Pregnancy ,Prenatal Exposure Delayed Effects ,Reproduction ,Androgens ,Twins, Dizygotic ,Humans ,Female - Abstract
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.
- Published
- 1998
14. Assortative mating for Cigarette Smoking and for Alcohol Consumption in Female Australian Twins and their Spouses
- Author
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A. Agrawal, A. C. Heath, J. D. Grant, M. L. Pergadia, K. K. Bucholz, P. A. F. Madden, D. J. Statham, and N. G. Martin
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Genetics ,Genetics (clinical) ,Ecology, Evolution, Behavior and Systematics - Published
- 2006
15. Foreword
- Author
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N. G. Martin, D. I. Boomsma, and M. C. Neale
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Genetics ,Genetics (clinical) ,Ecology, Evolution, Behavior and Systematics - Published
- 1989
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