Biomedical subjects

Nicholas G Martin

Publications and source records attributed to Nicholas G Martin.

At least 55 records · Page 3Linked to original sources

PubMed2006

Use of latent profile analysis to identify eating disorder phenotypes in an adult Australian twin cohort.

CONTEXT: The relationships among the different eating disorders that exist in the community are poorly understood, especially for residual disorders in which bingeing or purging occurs in the absence of other behaviors. OBJECTIVE: To examine a community sample for the number of mutually exclusive weight and eating profiles. DESIGN: Data regarding lifetime eating disorder symptoms and weight range were submitted to a latent profile analysis. Profiles were compared regarding personality, current eating and weight, retrospectively reported life events, and lifetime depressive psychopathology. SETTING: Longitudinal study among female twins from the Australian Twin Registry in whom eating was assessed by a telephone interview. PARTICIPANTS: A community sample of 1002 twins (individuals) who had participated in earlier waves of data collection. MAIN OUTCOME MEASURES: Number and clinical character of latent profiles. RESULTS: The best fit was a 5-profile solution with women who were (1) of normal weight with few lifetime eating disorders (4.3%), (2) overweight (10.6% had a lifetime eating disorder), (3) underweight and generally had no eating disorders except for 5.3% who had restricting anorexia nervosa, (4) of low to normal weight (89.0% had a lifetime eating disorder), and (5) obese (37.0% had a lifetime eating disorder). Each profile contained more than 1 type of lifetime eating disorder except for the third profile. Women in the first and third profiles had the best functioning, with women in the fourth and fifth profiles having similarly poorer functioning. The women in the fourth group had a symptom profile distinctive from the other 4 groups in terms of severity; they were also more likely to have had lifetime major depression and suicidality. CONCLUSION: Lifetime weight ranges and the severity of eating disorder symptoms affected clustering more than the type of eating disorder symptom.

Adult↗

PubMed2006

Genetic analyses of DSM-IV nicotine withdrawal in adult twins.

BACKGROUND: We examined whether there are genetic influences on nicotine withdrawal, and whether there are genetic factors specific to nicotine withdrawal, after controlling for factors responsible for risk of progression beyond experimentation with cigarettes and for quantity smoked (average number of cigarettes per day at peak lifetime use). METHOD: Epidemiologic and genetic analyses were conducted using telephone diagnostic interview data from young adult Australian twins reporting any cigarette use (3026 women, 2553 men; mean age 30 years). RESULTS: Genetic analysis of the eight symptoms of DSM-IV nicotine withdrawal suggests heritability is intermediate for most symptoms (26-43%), and similar in men and women. The exceptions were depressed mood upon withdrawal, which had stronger additive genetic influences in men (53%) compared to women (29%), and decreased heart rate, which had low heritability (9%). Although prevalence rates were substantially lower for DSM-IV nicotine withdrawal syndrome (15.9%), which requires impairment, than for the DSM-IV nicotine dependence withdrawal criterion (43.6%), heritability was similar for both measures: as high as 47%. Genetic modeling of smoking more than 1 or 2 cigarettes lifetime ('progression'), quantity smoked and nicotine withdrawal found significant genetic overlap across all three components of nicotine use/dependence (genetic correlations = 0.53-0.76). Controlling for factors associated with risk of cigarette smoking beyond experimentation and quantity smoked, evidence for genetic influences specific to nicotine withdrawal (up to 23% of total variance) remained. CONCLUSIONS: Our results suggest that at least some individuals become 'hooked' or progress in the smoking habit, in part, because of a vulnerability to nicotine withdrawal.

Adult↗

PubMed2006

A genetically informed study of the processes underlying the association between parental marital instability and offspring adjustment.

Parental divorce is associated with problematic offspring adjustment, but the relation may be due to shared genetic or environmental factors. One way to test for these confounds is to study offspring of twins discordant for divorce. The current analyses used this design to separate the mechanisms responsible for the association between parental divorce, experienced either before or after the age of 16, and offspring well-being. The results were consistent with a causal role of divorce in earlier initiation of sexual intercourse and emotional difficulties, in addition to a greater probability of educational problems, depressed mood, and suicidal ideation. In contrast, the increased risk for cohabitation and earlier initiation of drug use was explained by selection factors, including genetic confounds. ((c) 2006 APA, all rights reserved).

Adult↗

PubMed2006

Family structure and age at menarche: a children-of-twins approach.

Girls who grow up in households with an unrelated adult male reach menarche earlier than peers, a finding hypothesized to be an evolutionary strategy for families under stress. The authors tested the alternative hypothesis that nonrandom selection into stepfathering due to shared environmental and/or genetic predispositions creates a spurious relation between stepfathering and early menarche. Using the unique controls for genetic and shared environmental experiences offered by the children-of-twins design, the authors found that cousins discordant for stepfathering did not differ in age of menarche. Moreover, controlling for mother's age of menarche eliminated differences in menarcheal age associated with stepfathering in unrelated girls. These findings strongly suggest selection, and not causation, accounts for the relationship between stepfathering and early menarche.

Adolescent↗

PubMed2006

A genetically informed study of the association between harsh punishment and offspring behavioral problems.

Conclusions about the effects of harsh parenting on children have been limited by research designs that cannot control for genetic or shared environmental confounds. The present study used a sample of children of twins and a hierarchical linear modeling statistical approach to analyze the consequences of varying levels of punishment while controlling for many confounding influences. The sample of 887 twin pairs and 2,554 children came from the Australian Twin Registry. Although corporal punishment per se did not have significant associations with negative childhood outcomes, harsher forms of physical punishment did appear to have specific and significant effects. The observed association between harsh physical punishment and negative outcomes in children survived a relatively rigorous test of its causal status, thereby increasing the authors' conviction that harsh physical punishment is a serious risk factor for children.

Adult↗

PubMed2006

A genome scan for epidermal skin pattern in adolescent twins reveals suggestive linkage on 12p13.31.

Deterioration in stratum corneum reticular patterning (skin pattern or skin wrinkling) has been associated with increased rates of solar keratoses and skin cancer. A previous analysis of data from the twin sample used in this investigation has shown that 86% of the variation in skin pattern is genetic at age 12 and 62% in an adult sample (mean age = 47.5). Variation due to genetic influences is likely to be influenced by more than one locus. Here, we present results of a genome-wide linkage scan of skin pattern in adolescent twins and siblings from 428 nuclear twin families. Sib-pair linkage analysis was performed on skin pattern data collected from twins at age 12 (378 informative families) and 14 (316 families). Suggestive linkage was found at marker D12S397 (12p13.31, logarithm of the odds (lod) 1.94), when the effect of the trait locus was modelled to influence the skin pattern equally at both ages 12 and 14. In the same analysis, a peak was seen at 4q23 with a lod score of 1.55. A possible candidate for the peak at 12p13.31 is the protease inhibitor, alpha-2-macroglobulin.

Adolescent↗

PubMed2006

A transdiagnostic approach to understanding eating disorders.

Categorical models dominate the eating disorder field, but the tandem use of categorical and dimensional models has been proposed. A transdiagnostic dimensional model, number of lifetime eating disorder behaviors (LEDB), was examined with respect to (1) its relationship to a variety of indicators of the individual's functioning, (2) the degree to which it was influenced by genetic and environmental risk factors, and (3) exposure to specific environmental risk factors. Data from self-report and interview from 1002 female twins (mean age = 34.91 years, SD = 2.09) were examined. While 15.4% women met criteria for a lifetime eating disorder, 29% had at least one LEDB. The dimensional measure provided an indicator of associated functioning, and was influenced primarily by the nonshared environment. The number of LEDB was associated with the degree of impaired functioning. This impairment was associated with conflict between parents and criticism from parents when growing up.

Adult↗

PubMed2006

Genetic and environmental influences on extreme personality dispositions in adolescent female twins.

BACKGROUND: The objective was to determine whether the pattern of environmental and genetic influences on deviant personality scores differs from that observed for the normative range of personality, comparing results in adolescent and adult female twins. METHODS: A sample of 2,796 female adolescent twins ascertained from birth records provided Junior Eysenck Personality Questionnaire data. The average age of the sample was 17.0 years (S.D. 2.3). Genetic analyses of continuous and extreme personality scores were conducted. Results were compared for 3,178 adult female twins. RESULTS: Genetic analysis of continuous traits in adolescent female twins were similar to findings in adult female twins, with genetic influences accounting for between 37% and 44% of the variance in Extraversion (Ex), Neuroticism (N), and Social Non-Conformity (SNC), with significant evidence of shared environmental influences (19%) found only for SNC in the adult female twins. Analyses of extreme personality characteristics, defined categorically, in the adolescent data and replicated in the adult female data, yielded estimates for high N and high SNC that deviated substantially (p < .05) from those obtained in the continuous trait analyses, and provided suggestive evidence that shared family environment may play a more important role in determining personality deviance than has been previously found when personality is viewed continuously. However, multiple-threshold models that assumed the same genetic and environmental determinants of both normative range variation and extreme scores gave acceptable fits for each personality dimension. CONCLUSIONS: The hypothesis of differences in genetic or environmental factors responsible for N and SNC among female twins with scores in the extreme versus normative ranges was partially supported, but not for Ex.

Adolescent↗

PubMed2006

Effects of variation at the ALDH2 locus on alcohol metabolism, sensitivity, consumption, and dependence in Europeans.

BACKGROUND: The low-activity variant of the aldehyde dehydrogenase 2 (ALDH2) gene found in East Asian populations leads to the alcohol flush reaction and reduces alcohol consumption and risk of alcohol dependence (AD). We have tested whether other polymorphisms in the ALDH2 gene have similar effects in people of European ancestry. METHODS: Serial measurements of blood and breath alcohol, subjective intoxication, body sway, skin temperature, blood pressure, and pulse were obtained in 412 twins who took part in an alcohol challenge study. Participants provided data on alcohol reactions, alcohol consumption, and symptoms related to AD at the time of the study and subsequently. Haplotypes based on 5 single-nucleotide polymorphisms (SNPs) were used in tests of the effects of variation in the ALDH2 gene on alcohol metabolism and alcohol's effects. RESULTS: The typed SNPs were in strong linkage disequilibrium and 2 complementary haplotypes comprised 83% of those observed. Significant effects of ALDH2 haplotype were observed for breath alcohol concentration, with similar but smaller and nonsignificant effects on blood alcohol. Haplotype-related variation in responses to alcohol, and reported alcohol consumption, was small and not consistently in the direction predicted by the effects on alcohol concentrations. CONCLUSIONS: Genetic variation in ALDH2 affects alcohol metabolism in Europeans. However, the data do not support the hypothesis that this leads to effects on alcohol sensitivity, consumption, or risk of dependence.

Adolescent↗

PubMed2006

Heritability and stability of resting blood pressure in Australian twins.

In Australian twins participating in three different studies (1979-1996), the contribution of genetic and environmental influences to variation in resting systolic (SBP) and diastolic blood pressure (DBP) was studied. The sample consisted of 368 monozygotic and 335 dizygotic twin pairs with measurements for both individuals. Blood pressure measurements in two studies were available for 115 complete twin pairs, and 49 twin pairs had measurements in three studies. This allowed assessment of blood pressure tracking over an average period of 12 years in the age range of 23 to 45 years. Multivariate analyses showed significant heritability (h2) of blood pressure in all studies (SBP h2 = 19%-56%, DBP h2 = 37%-52%). In addition, the analyses showed that the blood pressure tracking was explained by the same set of genetic factors. These results replicate an earlier finding in Dutch twins that also showed stability of the contribution of genetic factors to blood pressure tracking.

Adult↗

PubMed2006

Handedness in twins: joint analysis of data from 35 samples.

Simultaneous analysis of handedness data from 35 samples of twins (with a combined sample size of 21,127 twin pairs) found a small but significant additive genetic effect accounting for 25.47% of the variance (95% confidence interval [CI] 15.69-29.51%). No common environmental influences were detected (C = 0.00; 95% CI 0.00-7.67%), with the majority of the variance, 74.53%, explained by factors unique to the individual (95% CI 70.49-78.67%). No significant heterogeneity was observed within studies that used similar methods to assess handedness, or across studies that used different methods. At an individual level the majority of studies had insufficient power to reject a purely unique environmental model due to insufficient power to detect familial aggregation. This lack of power is seldom mentioned within studies, and has contributed to the misconception that twin studies of handedness are not informative.

Functional Laterality↗

PubMed2006

Migraine with aura and migraine without aura are not distinct entities: further evidence from a large Dutch population study.

It is often debated whether migraine with aura (MA) and migraine without aura (MO) are etiologically distinct disorders. A previous study using latent class analysis (LCA) in Australian twins showed no evidence for separate subtypes of MO and MA. The aim of the present study was to replicate these results in a population of Dutch twins and their parents, siblings and partners (N = 10,144). Latent class analysis of International Headache Society (IHS)-based migraine symptoms resulted in the identification of 4 classes: a class of unaffected subjects (class 0), a mild form of nonmigrainous headache (class 1), a moderately severe type of migraine (class 2), typically without neurological symptoms or aura (8% reporting aura symptoms), and a severe type of migraine (class 3), typically with neurological symptoms, and aura symptoms in approximately half of the cases. Given the overlap of neurological symptoms and nonmutual exclusivity of aura symptoms, these results do not support the MO and MA subtypes as being etiologically distinct. The heritability in female twins of migraine based on LCA classification was estimated at .50 (95% confidence intervals [CI] .27 - .59), similar to IHS-based migraine diagnosis (h2 = .49, 95% CI .19-.57). However, using a dichotomous classification (affected-unaffected) decreased heritability for the IHS-based classification (h2 = .33, 95% CI .00-.60), but not the LCA-based classification (h2 = .51, 95% CI .23-.61). Importantly, use of the LCA-based classification increased the number of subjects classified as affected. The heritability of the screening question was similar to more detailed LCA and IHS classifications, suggesting that the screening procedure is an important determining factor in genetic studies of migraine.

Adolescent↗

PubMed2006

Longitudinal genetic analysis of plasma lipids.

The consensus from published studies is that plasma lipids are each influenced by genetic factors, and that this contributes to genetic variation in risk of cardiovascular disease. Heritability estimates for lipids and lipoproteins are in the range .48 to .87, when measured once per study participant. However, this ignores the confounding effects of biological variation measurement error and ageing, and a truer assessment of genetic effects on cardiovascular risk may be obtained from analysis of longitudinal twin or family data. We have analyzed information on plasma high-density lipoprotein (HDL) and low-density lipoprotein (LDL) cholesterol, and triglycerides, from 415 adult twins who provided blood on two to five occasions over 10 to 17 years. Multivariate modeling of genetic and environmental contributions to variation within and across occasions was used to assess the extent to which genetic and environmental factors have long-term effects on plasma lipids. Results indicated that more than one genetic factor influenced HDL and LDL components of cholesterol, and triglycerides over time in all studies. Nonshared environmental factors did not have significant long-term effects except for HDL. We conclude that when heritability of lipid risk factors is estimated on only one occasion, the existence of biological variation and measurement errors leads to underestimation of the importance of genetic factors as a cause of variation in long-term risk within the population. In addition our data suggest that different genes may affect the risk profile at different ages.

Adolescent↗

PubMed2006

Subtypes of illicit drug users: a latent class analysis of data from an Australian twin sample.

This article applies methods of latent class analysis (LCA) to data on lifetime illicit drug use in order to determine whether qualitatively distinct classes of illicit drug users can be identified. Self-report data on lifetime illicit drug use (cannabis, stimulants, hallucinogens, sedatives, inhalants, cocaine, opioids and solvents) collected from a sample of 6265 Australian twins (average age 30 years) were analyzed using LCA. Rates of childhood sexual and physical abuse, lifetime alcohol and tobacco dependence, symptoms of illicit drug abuse/dependence and psychiatric comorbidity were compared across classes using multinomial logistic regression. LCA identified a 5-class model: Class 1 (68.5%) had low risks of the use of all drugs except cannabis; Class 2 (17.8%) had moderate risks of the use of all drugs; Class 3 (6.6%) had high rates of cocaine, other stimulant and hallucinogen use but lower risks for the use of sedatives or opioids. Conversely, Class 4 (3.0%) had relatively low risks of cocaine, other stimulant or hallucinogen use but high rates of sedative and opioid use. Finally, Class 5 (4.2%) had uniformly high probabilities for the use of all drugs. Rates of psychiatric comorbidity were highest in the polydrug class although the sedative/opioid class had elevated rates of depression/suicidal behaviors and exposure to childhood abuse. Aggregation of population-level data may obscure important subgroup differences in patterns of illicit drug use and psychiatric comorbidity. Further exploration of a 'self-medicating' subgroup is needed.

Australia↗

PubMed2006

Empirical evaluation of the genetic similarity of samples from twin registries in Australia and the Netherlands using 359 STRP markers.

One way to achieve the large sample sizes required for genetic studies of complex traits is to combine samples collected by different groups. It is not often clear, however, whether this practice is reasonable from a genetic perspective. To assess the comparability of samples from the Australian and the Netherlands twin studies, we estimated Fst (the proportion of total genetic variability attributable to genetic differences between cohorts) based on 359 short tandem repeat polymorphisms in 1068 individuals. Fst was estimated to be 0.30% between the Australian and the Netherlands cohorts, a smaller value than between many European groups. We conclude that it is reasonable to combine the Australian and the Netherlands samples for joint genetic analyses.

Australia↗

PubMed2006

Sex differences in symptoms of depression in unrelated individuals and opposite-sex twin and sibling pairs.

Diagnosis of a major depressive episode by the Diagnostic and Statistical Manual of Mental Disorders of the American Psychiatric Association requires 5 out of 9 symptoms to be present. Therefore, individuals may differ in the specific symptoms they experience and reach a diagnosis of depression via different pathways. It has been suggested that depressed women more often report symptoms of sleep disturbance, appetite or weight disturbance, fatigue, feelings of guilt/worthlessness and psychomotor retardation than depressed men. In the current study, we investigate whether depressed men and women differ in the symptoms they report. Two samples were selected from a sample of Dutch and Australian twins and siblings. First, Dutch and Australian unrelated depressed individuals were selected. Second, a matched epidemiological sample was created consisting of opposite-sex twin and sibling pairs in which both members were depressed. No sex differences in prevalence rates for symptoms were found, with the exception of decreased weight in women in the sample of unrelated individuals. In general, the similarities in symptoms seem to far out-weigh the differences in symptoms between men and women. This signifies that men and women are alike in their symptom profiles for major depression and genes for depression are probably expressed in the same way in the two sexes.

Adult↗

PubMed2005

A possible smoking susceptibility locus on chromosome 11p12: evidence from sex-limitation linkage analyses in a sample of Australian twin families.

Many twin studies have identified sex differences in the influence of genetic and environmental factors on smoking behaviors. We explore the evidence for sex differences for smoking initiation and cigarette consumption in a sample of Australian twin families, and extend these models to incorporate sex differences in linkage analyses for these traits. We further examine the impact of including or excluding non-smokers in genetic analyses of tobacco consumption. Accounting for sex differences improved linkage results in some instances. We identified one region suggestive of linkage on chromosome 11p12. This locus, as well as another region identified on chromosome 6p12, replicates regions identified in previous studies.

Adult↗

PubMed2005

A linkage study of academic skills defined by the Queensland core skills test.

This study used genome-wide linkage analysis to detect Quantitative Trait Loci (QTLs) implicated in variation in general academic achievement as measured by the Queensland Core Skills Test (QCST) (Queensland Studies Authority, 2004). Data from 210 families were analysed. While no empirically derived significant or suggestive peaks for general academic achievement were indicated a peak on chromosome 2 was observed in a region where Posthuma et al. (2005) reported significant linkage for Performance IQ (PIQ) and suggestive linkage for Full Scale IQ (FSIQ), and Luciano et al. (this issue) observed significant linkage for PIQ and word reading. A peak on chromosome 18 was also observed approximately 20 cM removed from a region recently implicated in reading achievement. In addition, on chromosomes 2 and 18 peaks for a number of specific academic skills, two of which were suggestive, coincided with the general academic achievement peaks. The findings suggest that variation in general academic achievement is influenced by genes on chromosome 2 which have broad influence on a variety of cognitive abilities.

Chromosome Mapping↗