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Biomedical subjects

Jennifer R Harris

Publications and source records attributed to Jennifer R Harris.

At least 19 recordsLinked to original sources
PubMed2006

Genetic influences on exercise participation in 37,051 twin pairs from seven countries.

BACKGROUND: A sedentary lifestyle remains a major threat to health in contemporary societies. To get more insight in the relative contribution of genetic and environmental influences on individual differences in exercise participation, twin samples from seven countries participating in the GenomEUtwin project were used. METHODOLOGY: Self-reported data on leisure time exercise behavior from Australia, Denmark, Finland, Norway, The Netherlands, Sweden and United Kingdom were used to create a comparable index of exercise participation in each country (60 minutes weekly at a minimum intensity of four metabolic equivalents). PRINCIPAL FINDINGS: Modest geographical variation in exercise participation was revealed in 85,198 subjects, aged 19-40 years. Modeling of monozygotic and dizygotic twin resemblance showed that genetic effects play an important role in explaining individual differences in exercise participation in each country. Shared environmental effects played no role except for Norwegian males. Heritability of exercise participation in males and females was similar and ranged from 48% to 71% (excluding Norwegian males). CONCLUSIONS: Genetic variation is important in individual exercise behavior and may involve genes influencing the acute mood effects of exercise, high exercise ability, high weight loss ability, and personality. This collaborative study suggests that attempts to find genes influencing exercise participation can pool exercise data across multiple countries and different instruments.

Adult↗
PubMed2006

Genetic and environmental influences on dimensional representations of DSM-IV cluster C personality disorders: a population-based multivariate twin study.

BACKGROUND: The DSM-IV cluster C Axis II disorders include avoidant (AVPD), dependent (DEPD) and obsessive-compulsive (OCPD) personality disorders. We aimed to estimate the genetic and environmental influences on dimensional representations of these disorders and examine the validity of the cluster C construct by determining to what extent common familial factors influence the individual PDs. METHOD: PDs were assessed using the Structured Interview for DSM-IV Personality (SIDP-IV) in a sample of 1386 young adult twin pairs from the Norwegian Institute of Public Health Twin Panel (NIPHTP). A single-factor independent pathway multivariate model was applied to the number of endorsed criteria for the three cluster C disorders, using the statistical modeling program Mx. RESULTS: The best-fitting model included genetic and unique environmental factors only, and equated parameters for males and females. Heritability ranged from 27% to 35%. The proportion of genetic variance explained by a common factor was 83, 48 and 15% respectively for AVPD, DEPD and OCPD. Common genetic and environmental factors accounted for 54% and 64% respectively of the variance in AVPD and DEPD but only 11% of the variance in OCPD. CONCLUSION: Cluster C PDs are moderately heritable. No evidence was found for shared environmental or sex effects. Common genetic and individual environmental factors account for a substantial proportion of the variance in AVPD and DEPD. However, OCPD appears to be largely etiologically distinct from the other two PDs. The results do not support the validity of the DSM-IV cluster C construct in its present form.

Adult↗
PubMed2006

Epidemiology and heritability of astigmatism in Norwegian twins: an analysis of self-reported data.

PURPOSE: To describe the occurrence and heritability of astigmatism in a population-based sample of Norwegian twins. METHODS: Self-reported history of astigmatism based on questionnaire responses was used to estimate the prevalence and incidence rates of astigmatism from birth through 31 years in 8,045 twins. Kaplan-Meier analysis and log-binomial regression were used to study the conditional and relative risk of astigmatism in twin pairs by sex and zygosity. Tetrachoric correlations and structural equation models were applied to estimate the genetic and environmental sources of variations in liability for astigmatism. RESULTS: Altogether 21.1% of males and 29.3% of females (p < 0.001) reported a positive history of astigmatism. Estimated incidence rates peaked in both sexes in the group aged 16-19 years and then decreased. Both conditional and relative risks of developing astigmatism were considerably higher in monozygotic than in dizygotic twins if a cotwin reported a positive history of astigmatism. The best-fitting biometrical model suggested that additive genetic, dominant genetic, and individual environmental effects explained 9% (95% CI: 0-40), 54% (95% CI: 20-69), and 38% (95% CI: 31-45) of the variation in the liability to astigmatism, respectively. No differences in heritability of astigmatism between the genders were found. CONCLUSIONS: The prevalence of self-reported astigmatism in twins is comparable with previous findings from Norway. Our results suggest considerable genetic contribution to the development of astigmatism in young adult Norwegian twins mainly due to dominant genetic effects, which are similar in both males and females.

Adolescent↗
PubMed2005

Characterizing individual differences in heat-pain sensitivity.

Heat induced pain has been shown to follow a positively accelerating power function for groups of subjects, yet the extent to which this applies to individual subjects is unknown. Statistical methods were developed for assessing the goodness of fit and reliability of the power function for data from individual subjects with the aim of using such functions for characterizing individual differences in heat-pain sensitivity. 175 subjects rated ascending and random series of contact heat stimuli with visual analogue scales for pain intensity (VAS-I) and unpleasantness (VAS-A). Curve fitting showed excellent model fit. Substitution of model estimates in place of observed VAS scores produced minimal bias in group means, about 0.3 VAS units in the ascending series and 1.0 in the random series, on a 0-100 scale. Individual power function exponents were considerably higher for the ascending than for the random series and somewhat higher for VAS-A than for VAS-I (means: ascending VAS-I=9.04, VAS-A=9.80; random VAS-I=4.95, VAS-A=5.67). The reliability of VAS estimates was high (>==.93), and for the ascending series it remained so when extrapolating 4 degrees C beyond the empirical range. Exponent reliability was high for the ascending series (VAS-I=.92; VAS-A=.91), but considerably lower for the random series (VAS-I=.69; VAS-A=.71). Individual differences constituted 60% of the total variance in pain ratings, whereas stimulus temperature accounted for only 40%. This finding underscores the importance of taking individual differences into account when performing pain studies.

Adult↗
PubMed2005

A comparison of genetic and environmental variance structures for asthma, hay fever and eczema with symptoms of the same diseases: a study of Norwegian twins.

BACKGROUND: We compared patterns of genetic and environmental influences on variation in liability for asthma, hay fever and eczema with those for symptoms of the same diseases, and determined how common sets of genes and environmental factors contribute to the relationship between diseases and symptoms among Norwegian twins. METHODS: Analyses were based on self-reported asthma, hay fever and eczema and symptoms of the same diseases among 3334 pairs of Norwegian twins aged 18-35 years. Structural equation modelling was conducted to estimate the genetic and environmental variance structures. RESULTS: For all diseases the concordances and the twin correlations were higher among monozygotic than among dizygotic twins. The results of the modelling confirmed that genetic effects were substantial for the diseases, and were more moderate for symptoms. The phenotypic correlation between disease and symptom was 0.67 for asthma and wheeze (a/w), 0.64 for hay fever and sneeze (hf/s), and 0.54 for eczema and itch (e/i). Decomposition of these correlations into genetic (G) and environmental (E) pathways revealed that G = 0.48 and E = 0.19 for a/w, G = 0.40 and E = 0.24 for hf/s, and G = 0.34 and E = 0.20 for e/i. For the diseases, the specific sources of genetic variance accounted for more variation than the specific environmental variance. Variance decomposition revealed that specific sources of variance were primarily explained by genetic effects for diseases and by environmental influences for symptoms. CONCLUSIONS: Genetic effects account for greater variation in reported diseases than symptoms. Co-occurrence of diseases and symptoms is mainly explained by genetic effects common to both phenotypes, but non-shared environment is also important.

Adult↗
PubMed2005

Birthweight and adult health in a population-based sample of Norwegian twins.

Population-based twin data were used to test (a) whether lower birthweight confers a greater risk of adult health disorders, and (b) whether within-pair birthweight differences in twins explain discordance for health outcomes. The sample consisted of 1201 monozygotic (MZ) male twins, 1048 dizygotic (DZ) male twins, 1679 MZ female twins, 1489 DZ female twins, and 2423 opposite-sex DZ twins, born in Norway between 1967 and 1979. The relationship between birthweight and self-reported health outcomes were studied using multivariable logistic regression. In the full sample (n = 7840), birthweight was negatively associated with risk for nearsightedness (odds ratio OR = 0.76, 95% CI: 0.65 - 0.92) and minimal brain disorder (OR = 0.27, 95% CI: 0.16-0.44) when adjusted for gestational age, sex, zygosity, age, education and body mass index after correction for intraclass correlations and multiple comparisons. Within-pair analysis of 159 MZ and 224 DZ pairs revealed that myopic twins were on average 2 g (p = .966) and 64 g (p = .040) lighter than nonmyopic twins in MZ and DZ pairs respectively, suggesting that genetic factors may play an important role in the associations between birthweight and nearsightedness. Within-pair analysis of twins discordant for a minimal brain disorder indicated that affected twins were 80 g (p = .655) and 85 g (p = .655) lighter than their healthy co-twins in MZ and DZ pairs respectively, although there were only 2 MZ and 2 DZ discordant pairs.

Adult↗
PubMed2005

Genetic factors in seizures: a population-based study of 47,626 US, Norwegian and Danish twin pairs.

The purpose of the study was to describe a large sample of twins reporting a history of seizures, to characterize seizures in the three subpopulations, and to estimate the relative importance of genetic and environmental factors in seizure occurrence. Seizure history was determined by questionnaires completed by twins in population-based twin registries in the United States, Norway and Denmark. Concordance rates were calculated for all seizure categories within and across twin populations. Of 47,626 twin pairs evaluated, 6234 reported a history of seizures in one or both twins. Concordance rates were significantly higher for monozygotic (MZ) versus dizygotic (DZ)pairs for all seizure categories within and across populations. The results of this study involving the largest unselected, population-based sample of twins with seizures assembled to date confirm the importance of genetic factors in determining risk for epilepsy, febrile seizures, other seizures and staring spells. This sample is likely to provide an important resource for studying the genetics of epilepsy subtypes and febrile seizures.

Adolescent↗
PubMed2005

Resolving the genetic and environmental sources of the correlation between height and intelligence: a study of nearly 2600 Norwegian male twin pairs.

The main aim of this paper was to resolve the correlation between intelligence test scores and standing height into genetic and environmental components. Data on 1181 identical and 1412 fraternal twin pairs (all males) were retrieved by matching files from the Norwegian Army with twin registries. The data were analyzed by means of a structural equation model comprising latent genetic, shared environmental and nonshared environmental factors and correlations between them. A major part of the height--intelligence correlation was due to correlated shared environments (59% of the phenotypic height--intelligence correlation), but statistically significant effects of correlated genes and nonshared environments were also found (respectively 35% and 6% of the phenotypic correlation).

Adolescent↗
PubMed2005

Subjective wellbeing and sleep problems: a bivariate twin study.

The relationship between subjective wellbeing (SWB) and self-reported sleep problems was investigated in a cohort of Norwegian twins aged 18 to 31 years. Questionnaire data from 8045 same- and opposite-sex twins were analyzed using structural equation modeling to explore the relative effects of genetic and environmental influences on phenotypic variance and covariance. Special attention was paid to sex-specific effects. The correlation between the phenotypes was estimated to be -.43. Univariate analyses indicated considerable genetic influences for both SWB and sleep problems, for male and female twins alike. The best fitting bivariate model specified additive genetic and individual environmental factors for both phenotypes, and nonadditive genetic effects for sleep problems, with no sex-specific effects. Genetic and environmental effects accounted for 60% and 40% of the phenotypic correlation, respectively. Additive genetic factors affecting the two phenotypes were correlated (-.85), suggesting that part of the genetic effects that positively influence SWB also protect against sleep problems. In conclusion, the results indicate considerable overlap in genetic etiology for SWB and sleep problems, for males and females alike.

Adolescent↗
PubMed2004

Undue influence of weight on self-evaluation: a population-based twin study of gender differences.

OBJECTIVE: To explore the extent to which genetic and environmental factors contribute to liability to placing undue importance on weight as an indicator of self-evaluation and to determine whether differences exist across genders in the nature and magnitude of these effects. METHOD: Self-report data were collected on 8,045 same-sex and opposite-sex twins, aged 18-31 years, from a population-based registry of Norwegian twins. Structural equation modeling was utilized to estimate the relative contribution of genetic and environmental factors to liability for undue influence of weight on self-evaluation, allowing for gender-specific effects. RESULTS: Individual variation in undue influence of weight on self-evaluation was best explained by shared and individual environmental influences. No significant gender differences were found. Shared environmental factors accounted for 31% of the variance. DISCUSSION: These results raise the possibility that there may be distinct sources of familial resemblance for different symptoms of bulimia nervosa as codified in the 4th ed. of the Diagnostic and Statistical Manual of Mental Disorders (American Psychiatric Association, 1994).

Adolescent↗
PubMed2004

Genetic and environmental influences on binge eating in the absence of compensatory behaviors: a population-based twin study.

OBJECTIVE: The current study explores the extent to which genetic and environmental factors influence liability to binge eating in the absence of compensatory behaviors (BE) in a population-based sample of twins. METHOD: Questionnaire data on 8,045 same-sex and opposite-sex twins, aged 18-31 years, from a Norwegian twin registry were used to assess BE during the last 6 months. RESULTS: The best-fitting biometrical model suggested that the heritability of BE was 41% (95% confidence interval [CI]: 0.31-0.50). Individual environmental factors accounted for the rest of the variance (59%; 95% CI: 0.50-0.69). No significant sex differences were found, but the statistical power to detect such effects was low. Shared environmental influences on the liability to BE in males could not be ruled out. DISCUSSION: The findings indicate significant additive genetic influences on BE, supporting the validity of the core features of binge eating disorder as a diagnostic category.

Adaptation, Psychological↗
PubMed2004

Genetic and environmental influences on the association between smoking and panic attacks in females: a population-based twin study.

BACKGROUND: Clinical and epidemiological studies have reported an association between lifetime cigarette-smoking and panic attacks. Several explanations for this relationship have been proposed, mostly focusing on direct causal pathways. The objective of this study was to investigate a hypothesis of shared vulnerability by examining whether panic attacks and cigarette-smoking share genetic or environmental liability factors. METHOD: Questionnaire data on 3172 female-female twins (1409 complete pairs), aged 18-31 years, from a population-based Norwegian twin registry, were used to calculate the correlation between genetic factors and the correlation between environmental factors that influence lifetime measures of panic attacks and daily smoking. RESULTS: The best-fitting biometrical twin model suggested that genetic factors influencing panic and smoking were uncorrelated. Shared or familial environmental factors were perfectly correlated, and accounted for 75 % of the association between the phenotypes. The correlation between individual environmental factors influencing the phenotypes was 0.25 (0.07-0.44). In the full model, the genetic correlation was 0.17 (0.00-1.00), and genetic and shared environmental factors respectively accounted for 18 % and 61 % of the co-variance between panic and smoking. CONCLUSION: The results suggest that panic attacks and lifetime smoking have few or no genetic liability factors in common. The shared environmental factors that influence the two phenotypes are identical. Liability to panic attacks in females appears to be more influenced by shared environmental factors than previously indicated by univariate studies.

Adolescent↗
PubMed2004

Psychiatric and medical symptoms in binge eating in the absence of compensatory behaviors.

OBJECTIVE: To explore the extent to which binge eating in the absence of compensatory behaviors (BE) is associated with psychiatric and medical symptoms in men and women and to control for the independent effects of BMI. RESEARCH METHODS AND PROCEDURES: A series of regression models was applied to questionnaire data on 8045 twins, 18 to 31 years old, from a population-based Norwegian registry. RESULTS: BE was significantly associated with elevated obesity, overweight, symptoms of eating disorders, symptoms of anxiety and depression, panic attacks, depressive episodes, and reduced life satisfaction in both men and women. In women, BE was independently associated with insomnia and early menarche. In men, BE was independently associated with specific phobia, daily smoking, alcohol use, use of pain medication, impairment due to mental health, neck-shoulder, lower back, and chronic muscular pain, and impairment due to physical health. Both men and women with BE reported higher rates of psychiatric treatment. DISCUSSION: Our results indicate that there is substantial comorbidity between BE and psychiatric symptoms independently of BMI for both men and women. Medical symptoms co-occur less frequently than previously reported from treatment-seeking populations in women. Across all domains, the array of symptoms exhibited by men with BE was broader than that observed in women with BE. This observation suggests the importance of considering gender differences in future studies of psychiatric and medical morbidity, binge eating, and obesity.

Adult↗
PubMed2004

Otitis media: genetic factors and sex differences.

Although genetic factors are recognised as major contributors to otitis media, the presence of sex differences in heritability needs clarification. The aim of this study was to estimate the relative contribution of genetic and environmental effects in otitis media liability with particular focus on sex differences. Data from a cohort of Norwegian twins born between 1967 and 1979 with repeated measures on recurrent childhood otitis media were analysed. Altogether the sample included 4247 twin pairs. The tetrachoric correlations for monozygotic twins were .71 and .65 for males and females respectively. In dizygotic twins the correlations were .35 and .25 for males and females, respectively, and was.34 in opposite sexed pairs. The contribution of genetic and environmental effects was analyzed using structural equation modeling. The best fitting model showed that additive genetic effects explained 72% and 61% of the variance in males and females, respectively. The remaining variance was attributed to individual environmental effects. A model specifying equal heritability estimates for males and females yielded an almost equivalent fit. We found substantial genetic effects for liability to otitis media. There is no evidence that different sets of genes influence liability in males and females, but there may be sex differences in the relative importance of genetic effects.

Cohort Studies↗
PubMed2003

Happiness and health: environmental and genetic contributions to the relationship between subjective well-being, perceived health, and somatic illness.

The aim was to identify genetic and environmental influences on the covariances between subjective well-being (SWB), perceived health, and somatic illness. Analyses were based on 6576 Norwegian twins aged 18-31. Heritabilities ranged from .24 to.66. SWB correlated .50 with perceived health, -.25 with musculoskeletal pain, and -.07 with allergy. Common genetic factors accounted for 45%-60% of associations. SWB and perceived health was to a high extent influenced by the same genes (r(g)=.72 and.82 for males and females, respectively). For SWB and musculoskeletal pain, r-sub(g) =-.29 and -.42 for males and females, respectively. Effects were partly sex specific. Environmental factors shared by twins did not affect the covariances. Results support a differentiated view of SWB-health relations, and imply that both genes and environment play important roles in the associations between well-being and health.

Adolescent↗
PubMed2003

Heritability of adult body height: a comparative study of twin cohorts in eight countries.

A major component of variation in body height is due to genetic differences, but environmental factors have a substantial contributory effect. In this study we aimed to analyse whether the genetic architecture of body height varies between affluent western societies. We analysed twin data from eight countries comprising 30,111 complete twin pairs by using the univariate genetic model of the Mx statistical package. Body height and zygosity were self-reported in seven populations and measured directly in one population. We found that there was substantial variation in mean body height between countries; body height was least in Italy (177 cm in men and 163 cm in women) and greatest in the Netherlands (184 cm and 171 cm, respectively). In men there was no corresponding variation in heritability of body height, heritability estimates ranging from 0.87 to 0.93 in populations under an additive genes/unique environment (AE) model. Among women the heritability estimates were generally lower than among men with greater variation between countries, ranging from 0.68 to 0.84 when an additive genes/shared environment/unique environment (ACE) model was used. In four populations where an AE model fit equally well or better, heritability ranged from 0.89 to 0.93. This difference between the sexes was mainly due to the effect of the shared environmental component of variance, which appears to be more important among women than among men in our study populations. Our results indicate that, in general, there are only minor differences in the genetic architecture of height between affluent Caucasian populations, especially among men.

Adult↗
PubMed2003

Sex differences in heritability of BMI: a comparative study of results from twin studies in eight countries.

Body mass index (BMI), a simple anthropometric measure, is the most frequently used measure of adiposity and has been instrumental in documenting the worldwide increase in the prevalence of obesity witnessed during the last decades. Although this increase in overweight and obesity is thought to be mainly due to environmental changes, i.e., sedentary lifestyles and high caloric diets, consistent evidence from twin studies demonstrates high heritability and the importance of genetic differences for normal variation in BMI. We analysed self-reported data on BMI from approximately 37,000 complete twin pairs (including opposite sex pairs) aged 20-29 and 30-39 from eight different twin registries participating in the GenomEUtwin project. Quantitative genetic analyses were conducted and sex differences were explored. Variation in BMI was greater for women than for men, and in both sexes was primarily explained by additive genetic variance in all countries. Sex differences in the variance components were consistently significant. Results from analyses of opposite sex pairs also showed evidence of sex-specific genetic effects suggesting there may be some differences between men and women in the genetic factors that influence variation in BMI. These results encourage the continued search for genes of importance to the body composition and the development of obesity. Furthermore, they suggest that strategies to identify predisposing genes may benefit from taking into account potential sex specific effects.

Adolescent↗