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Twin Study (twin + study)
Selected AbstractsSerum Lipid Levels and Cognitive Change in Late LifeJOURNAL OF AMERICAN GERIATRICS SOCIETY, Issue 3 2010Chandra A. Reynolds PhD OBJECTIVES: To assess the effect of lipids and lipoproteins on longitudinal cognitive performance and cognitive health in late life and to consider moderating factors such as age and sex that may clarify conflicting prior evidence. DESIGN: Prospective cohort study. SETTING: A 16-year longitudinal study of health and cognitive aging. PARTICIPANTS: Eight hundred nineteen adults from the Swedish Adoption Twin Study of Aging aged 50 and older at first cognitive testing, including 21 twin pairs discordant for dementia. MEASUREMENTS: Up to five occasions of cognitive measurements encompassing verbal, spatial, memory, and perceptual speed domains across a 16-year span; baseline serum lipids and lipoproteins including high-density lipoprotein cholesterol (HDL-C), apolipoprotein (apo)A1, apoB, total serum cholesterol, and triglycerides. RESULTS: The effect of lipids on cognitive change was most evident before age 65. In women, higher HDL-C and lower apoB and triglycerides predicted better maintenance of cognitive abilities, particularly verbal ability and perceptual speed, than age. Lipid values were less predictive of cognitive trajectories in men and, where observed, were in the contrary direction (i.e., higher total cholesterol and apoB values predicted better perceptual speed performance though faster rates of decline). In twin pairs discordant for dementia, higher total cholesterol and apoB levels were observed in the twin who subsequently developed dementia. CONCLUSION: High lipid levels may constitute a more important risk factor for cognitive health before age 65 than after. Findings for women are consistent with clinical recommendations, whereas for men, the findings correspond with earlier age-associated shifts in lipid profiles and the importance of lipid homeostasis to cognitive health. [source] Long-Term Leisure Time Physical Activity and Properties of Bone: A Twin Study,,JOURNAL OF BONE AND MINERAL RESEARCH, Issue 8 2009Hongqiang Ma Abstract Effects of physical activity on bone properties, when controlled for genetic effects, are not fully understood. We aimed to study the association between long-term leisure time physical activity (LTPA) and bone properties using twin pairs known to be discordant for leisure time physical activity for at least 30 yr. Volumetric BMD and geometric properties were measured at the tibia shaft and distal end using pQCT in 16 middle-aged (50,74 yr) same-sex twin pairs (seven monozygotic [MZ] and nine dizygotic [DZ] pairs) selected from a population-based cohort. Paired differences between active and inactive co-twins were studied. Active members of MZ twin pairs had larger cortical bone cross-sectional area (intrapair difference: 8%, p = 0.006), thicker cortex (12%, p = 0.003), and greater moment of inertia (Imax, 20%, p = 0.024) at the tibia shaft than their inactive co-twins. At the distal tibia, trabecular BMD (12%, p = 0.050) and compressive strength index (18%, p = 0.038) were also higher in physically active MZ pair members than their inactive co-twins. The trends were similar, but less consistently so, in DZ pairs as in MZ pairs. Our genetically controlled study design shows that LTPA during adulthood strengthens bones in a site-specific manner, that is, the long bone shaft has a thicker cortex, and thus higher bending strength, whereas the distal bone has higher trabecular density and compressive strength. These results suggest that LTPA has a potential causal role in decreasing the long-term risk of osteoporosis and thus preventing osteoporotic fractures. [source] Use of snus and risk for cardiovascular disease: results from the Swedish Twin RegistryJOURNAL OF INTERNAL MEDICINE, Issue 6 2009J. Hansson Abstract. Objective. To study the association between snus use and the risk for cardiovascular disease, i.e. ischemic heart disease and stroke. Design. Cohort study. Setting. Sweden. Subjects. Sixteen thousand six hundred and forty-two male Swedish twins participating in the Screening Across the Lifespan Twin Study, conducted in 1998,2002, were followed for incident cardiovascular disease. Participants were without a history of cardiovascular disease at baseline and incident cases were identified via the Swedish Cause of Death Register and Hospital Discharge Register. Results. Overall, there was no association between use of snus and risk for cardiovascular disease. Current snus users, without a smoking history, had a relative risk of 1.00 (95% confidence interval 0.69,1.46) for cardiovascular disease as compared to non users. Corresponding relative risks for ischemic heart disease and stroke were 0.85 (95% confidence interval 0.51,1.41) and 1.18 (95% confidence interval 0.67,2.08), respectively. In smoking adjusted models, risk estimates for ischemic heart disease in relation to snus use were all close to unity regardless of timing or intensity of snus use. However, current heavy snus users (consuming more than four cans week,1) had a relative risk for stroke of 1.75 (95% confidence interval 0.95,3.21). Conclusion. These data do not support any strong association between snus use and risk for cardiovascular disease. [source] Stability and Change in Personality Traits From Late Adolescence to Early Adulthood: A Longitudinal Twin StudyJOURNAL OF PERSONALITY, Issue 2 2008Daniel M. Blonigen ABSTRACT We conducted a longitudinal-biometric study examining stability and change in personality from ages 17 to 24 in a community sample of male and female twins. Using Tellegen's (in press) Multidimensional Personality Questionnaire (MPQ), facets of Negative Emotionality (NEM) declined substantially at the mean and individual levels, whereas facets of Constraint (CON) increased over time. Furthermore, individuals in late adolescence who were lowest on NEM and highest on CON remained the most stable over time, whereas those exhibiting the inverse profile (higher NEM, lower CON) changed the most in a direction towards growth and maturity. Analyses of gender differences yielded greater mean-level increases over time for women as compared to men on facets of CON and greater mean-level increases for men than women on facets of Agentic Positive Emotionality (PEM). Biometric analyses revealed rank-order stability in personality to be largely genetic, with rank-order change mediated by both the nonshared environment (and error) as well as genes. Findings correspond with prior evidence of a normative trend toward growth and maturity in personality during emerging adulthood. [source] Mood-Related Drinking Motives Mediate the Familial Association Between Major Depression and Alcohol DependenceALCOHOLISM, Issue 8 2009Kelly C. Young-Wolff Background:, Major depression and alcohol dependence co-occur within individuals and families to a higher than expected degree. This study investigated whether mood-related drinking motives mediate the association between major depression and alcohol dependence, and what the genetic and environmental bases are for this relationship. Methods:, The sample included 5,181 individuals from the Virginia Adult Twin Study of Psychiatric and Substance Use Disorders, aged 30 and older. Participants completed a clinical interview which assessed lifetime major depression, alcohol dependence, and mood-related drinking motives. Results:, Mood-related drinking motives significantly explained the depression-alcohol dependence relationship at both the phenotypic and familial levels. Results from twin analyses indicated that for both males and females, the familial factors underlying mood-related drinking motives accounted for virtually all of the familial variance that overlaps between depression and alcohol dependence. Conclusions:, The results are consistent with an indirect role for mood-related drinking motives in the etiology of depression and alcohol dependence, and suggest that mood-related drinking motives may be a useful index of vulnerability for these conditions. [source] Genetic and environmental influences on the transmission of parental depression to children's depression and conduct disturbance: an extended Children of Twins studyTHE JOURNAL OF CHILD PSYCHOLOGY AND PSYCHIATRY AND ALLIED DISCIPLINES, Issue 6 2010Judy L. Silberg Background:, Despite the increased risk of depression and conduct problems in children of depressed parents, the mechanism by which parental depression affects their children's behavioral and emotional functioning is not well understood. The present study was undertaken to determine whether parental depression represents a genuine environmental risk factor in children's psychopathology, or whether children's depression/conduct can be explained as a secondary consequence of the genetic liability transmitted from parents to their offspring. Methods:, Children of Twins (COT) data collected on 2,674 adult female and male twins, their spouses, and 2,940 of their children were used to address whether genetic and/or family environmental factors best account for the association between depression in parents and depression and conduct problems in their children. Data collected on juvenile twins from the Virginia Twin Study of Adolescent Behavioral Development (VTSABD) were also included to estimate child-specific genetic and environmental influences apart from those effects arising from the transmission of the parental depression itself. The fit of alternative Children of Twin models were evaluated using the statistical program Mx. Results:, The most compelling model for the association between parental and juvenile depression was a model of direct environmental risk. Both family environmental and genetic factors accounted for the association between parental depression and child conduct disturbance. Conclusions:, These findings illustrate how a genetically mediated behavior such as parental depression can have both an environmental and genetic impact on children's behavior. We find developmentally specific genetic factors underlying risk to juvenile and adult depression. A shared genetic liability influences both parental depression and juvenile conduct disturbance, implicating child conduct disturbance (CD) as an early indicator of genetic risk for depression in adulthood. In summary, our analyses demonstrate differences in the impact of parental depression on different forms of child psychopathology, and at various stages of development. [source] Electrocardiographic Indices of Left Ventricular Hypertrophy and Repolarization Phase Share the Same Genetic Influences: A Twin StudyANNALS OF NONINVASIVE ELECTROCARDIOLOGY, Issue 4 2009Sara Mutikainen M.Sc. Background: Both left ventricular hypertrophy (LVH) and repolarization phase (RP) are known to be attributable to genetic influences, but less is known whether they share same genetic influences. The aim of this study was to investigate to what extent individual differences in electrocardiographic (ECG) LVH and RP are explained by genetic and environmental influences and whether these influences are shared between these two traits. Methods: Resting ECG recordings were obtained from 186 monozygotic and 203 dizygotic female twin individuals, aged 63 to 76 years. Latent factors, called LVH and RP, were formed to condense the information obtained from LVH indices (Cornell voltage and Cornell product) and T-wave amplitudes (leads V5 and II), respectively. Multivariate quantitative genetic modeling was used both to decompose the phenotypic variances into additive genetic, common environmental, and unique environmental influences, and for the calculation of genetic and environmental correlations between LVH and RP. Results: Additive genetic influences explained 16% of individual differences in LVH and 74% in RP. The remaining individual differences were explained by both common and unique environmental influences. The genetic correlation and unique environmental correlation between LVH and RP were ,0.93 and ,0.05, respectively. Conclusions: In older women without overt cardiac diseases, RP is under stronger genetic control than LVH. The majority of genetic influences are shared between LVH and RP whereas environmental influences are mainly specific to each. [source] Genetic Influences on Resting Electrocardiographic Variables in Older Women: A Twin StudyANNALS OF NONINVASIVE ELECTROCARDIOLOGY, Issue 1 2009Sara Mutikainen M.Sc. Background: Previous studies in young and middle-aged men and women have shown that resting electrocardiographic (ECG) variables are influenced by genetic factors. However, the extent to which resting ECG variables are influenced by genetic factors in older women is unknown. Thus, the aim of this study was to estimate the relative contribution of genetic and environmental influences to individual differences in resting ECG variables among older female twins without overt cardiac diseases. Methods: Resting ECG recordings were obtained from 186 monozygotic and 203 dizygotic twin individuals, aged 63,76 years. Quantitative genetic modeling was used to decompose the phenotypic variance in each resting ECG variable into additive genetic, dominance genetic, shared environmental, and unique environmental influences. Results: The results showed that individual differences in the majority of the resting ECG variables were moderately to highly explained by additive genetic influences, ranging from 32% for T axis to 72% for TV5. The results also suggested dominance genetic influences on QRS duration, TV1, and Sokolow,Lyon voltage (36%, 53%, and 57%, respectively). Unique environmental influences were important for each resting ECG variable, whereas shared environmental influences were detected only for QT interval and QTc. Conclusion: In older women without overt cardiac diseases, genetic influences explain a moderate to high proportion of individual differences in the majority of the resting ECG variables. Genetic influences are especially strong for T-wave amplitudes, left ventricular mass, and hypertrophy indices, whereas other variables, including heart rate, intervals, and axes, are more affected by environmental influences. [source] Genetic and environmental influences on the transmission of parental depression to children's depression and conduct disturbance: an extended Children of Twins studyTHE JOURNAL OF CHILD PSYCHOLOGY AND PSYCHIATRY AND ALLIED DISCIPLINES, Issue 6 2010Judy L. Silberg Background:, Despite the increased risk of depression and conduct problems in children of depressed parents, the mechanism by which parental depression affects their children's behavioral and emotional functioning is not well understood. The present study was undertaken to determine whether parental depression represents a genuine environmental risk factor in children's psychopathology, or whether children's depression/conduct can be explained as a secondary consequence of the genetic liability transmitted from parents to their offspring. Methods:, Children of Twins (COT) data collected on 2,674 adult female and male twins, their spouses, and 2,940 of their children were used to address whether genetic and/or family environmental factors best account for the association between depression in parents and depression and conduct problems in their children. Data collected on juvenile twins from the Virginia Twin Study of Adolescent Behavioral Development (VTSABD) were also included to estimate child-specific genetic and environmental influences apart from those effects arising from the transmission of the parental depression itself. The fit of alternative Children of Twin models were evaluated using the statistical program Mx. Results:, The most compelling model for the association between parental and juvenile depression was a model of direct environmental risk. Both family environmental and genetic factors accounted for the association between parental depression and child conduct disturbance. Conclusions:, These findings illustrate how a genetically mediated behavior such as parental depression can have both an environmental and genetic impact on children's behavior. We find developmentally specific genetic factors underlying risk to juvenile and adult depression. A shared genetic liability influences both parental depression and juvenile conduct disturbance, implicating child conduct disturbance (CD) as an early indicator of genetic risk for depression in adulthood. In summary, our analyses demonstrate differences in the impact of parental depression on different forms of child psychopathology, and at various stages of development. [source] Genetic influences on reading difficulties in boys and girls: the Colorado twin studyDYSLEXIA, Issue 1 2006Jesse L. Hawke Abstract To test the hypothesis that the genetic etiology for reading disability may differ in males and females, data from identical and fraternal twin pairs were analysed using both concordance and multiple regression methods. The sample included 264 identical (129 male, 135 female) and 214 same-sex fraternal (121 male, 93 female) twin pairs in which at least one member of each pair had reading difficulties. The difference between the identical and fraternal twin pair concordance rates was slightly larger for females than for males, suggesting a possible sex difference in etiology; however, a loglinear analysis of the three-way interaction of sex, zygosity, and concordance was not significant (p,0.17). The estimate of group heritability (hg2), a standardized measure of the extent to which reading difficulties are due to genetic influences, was somewhat greater for females than males (0.65 vs 0.54), but this difference was also not significant (p,0.35). Gender differences in hg2 were larger for younger children (less than 11.5 years of age) than for older children. However, the three-way interaction of sex, zygosity, and age was not significant when age was treated either categorically (p,0.86) or continuously (p,0.71). Thus, results of this study provide little or no evidence for a differential genetic etiology of reading difficulties in males and females. Copyright © 2005 John Wiley & Sons, Ltd. [source] Early cannabis use and DSM-IV nicotine dependence: a twin studyADDICTION, Issue 11 2008Arpana Agrawal ABSTRACT Background Evidence suggests that cannabis users are at increased risk for cigarette smoking,if so, this may potentially be the single most alarming public health challenge posed by cannabis use. We examine whether cannabis use prior to age 17 years is associated with an increased likelihood of DSM-IV nicotine dependence and the extent to which genetic and environmental factors contribute to this association. Methods A population-based cohort of 24,36-year-old Australian male and female twins (n = 6257, 286 and 229 discordant pairs) was used. The co-twin,control method, with twin pairs discordant for early cannabis use, was used to examine whether, after controlling for genetic and familial environmental background, there was evidence for an additional influence of early cannabis use on DSM-IV nicotine dependence. Bivariate genetic models were fitted to the full data set to quantify the genetic correlation between early cannabis use and nicotine dependence. Results The early cannabis-using twin was about twice as likely to report nicotine dependence, when compared to their co-twin who had experimented with cigarettes but had never used cannabis. Even when analyses were restricted to cannabis users, earlier age cannabis use onset conferred greater risk (1.7) for nicotine dependence than did later onset. This association was governed largely by common genetic liability to early cannabis use and nicotine dependence, as demonstrated by genetic correlations of 0.41,0.52. Conclusions Early-onset cannabis users are at increased risk for nicotine dependence, but this risk is attributable largely to common genetic vulnerability. There is no evidence for a causal relationship between cannabis use and nicotine dependence. [source] Physical activity in adolescence and smoking in young adulthood: a prospective twin cohort studyADDICTION, Issue 7 2007Urho M. Kujala ABSTRACT Aims To control for familial confounds, we studied the association between adolescent physical activity and later smoking in twin siblings discordant for their baseline physical activity. Design and measurements In this prospective population-based twin study, we asked whether persistent physical activity/inactivity in adolescence (assessed at 16, 17 and 18.5 years) predicted questionnaire-reported daily smoking at ages 22,27. Twins who, on the three baseline questionnaires, consistently reported frequent leisure physical activity (more than three times weekly) were classified as persistent exercisers, those who exercised less than three times monthly were called persistently inactive, others were occasional exercisers. Setting Finland. Participants A total of 4240 individuals, including 1870 twin pairs. Findings In analyses of individual twins, compared to persistent activity, persistent physical inactivity predicted increased risk of daily smoking (age- and sex-adjusted odds ratio 5.53, 95% confidence interval 3.88,7.88, P < 0.001). The risk remained elevated even after excluding all those who had smoked 50 cigarettes or more life-time at baseline and adjusted for educational level in adolescence. In within-pair analyses compared to the active members of discordant twin pairs, the physically inactive co-twins had increased risk of future daily smoking (sex-adjusted odds ratio 3.39, 95% confidence interval 1.56,7.39, P = 0.002). Conclusions Persistent physical inactivity in adolescence relates to adult smoking, even after familial factors are taken into account. [source] Developmental path between language and autistic-like impairments: a twin studyINFANT AND CHILD DEVELOPMENT, Issue 2 2008Katharina Dworzynski Abstract Autism spectrum disorders (ASDs) are diagnosed when individuals show impairments in three behavioural domains: communication, social interactions, and repetitive, restrictive behaviours and interests (RRBIs). Recent data suggest that these three sets of behaviours are genetically heterogeneous. Early language delay is strongly associated with ASD, but the basis for this association and the relationship with individual sub-domains of ASD has not been systematically investigated. In the present study, data came from a population-based twin sample with language development data at 2,4 years, measured by the MacArthur Communicative Development Inventory (MCDI), and data at 8 years using the Childhood Asperger Syndrome Test (CAST). For the total CAST and the three subscales at 8 years, approximately 300 same-sex twin pairs were selected as showing extreme autistic-like traits (ALTs), defined here as pairs in which at least one member of the twin pair scored in the highest 5% of the distribution. Phenotypic analyses indicated that children showing extreme social and communication ALTs (but not the RRBI subscale) at 8 years were below average in language development at 2,4 years. A regression model for selected twin data suggested that genetic influences account for this overlap, but that these effects are only in part mediated by genes that are shared between language and extreme autistic traits. Copyright © 2008 John Wiley & Sons, Ltd. [source] Undue influence of weight on self-evaluation: A population-based twin study of gender differencesINTERNATIONAL JOURNAL OF EATING DISORDERS, Issue 2 2004Ted Reichborn-Kjennerud Abstract 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). © 2004 by Wiley Periodicals, Inc. Int J Eat Disord 35: 123,132, 2004. [source] Undue influence of weight on self-evaluation: A population-based twin study of gender differencesINTERNATIONAL JOURNAL OF EATING DISORDERS, Issue 2 2004Ulrike Schmidt No abstract is available for this article. [source] Genetic Contribution to Bone Metabolism, Calcium Excretion, and Vitamin D and Parathyroid Hormone RegulationJOURNAL OF BONE AND MINERAL RESEARCH, Issue 2 2001D. Hunter Abstract A classical twin study was performed to assess the relative contribution of genetic and environmental factors to bone metabolism, calcium homeostasis, and the hormones regulating them. It was examined further whether the genetic effect is menopause dependent. The subjects were 2136 adult twins (98.3% female): 384 monozygotic (MZ) and 684 dizygotic (DZ) twin pairs. The intraclass correlations were calculated, and maximum likelihood model fitting was used to estimate genetic and environmental variance components. The intraclass correlations for all of the variables assessed were higher in MZ twin pairs. The heritabilities (95% CIs) obtained from model fitting for hormones regulating bone metabolism and calcium homeostasis were parathyroid hormone (PTH), 60% (54,65%); 25-hydroxyvitamin D [25(OH)D]; 43% (28,57%), 1,25-hydroxyvitamin D [1,25(OH)], 65% (53,74%); and vitamin D binding protein 62% (56,66%). The heritabilities (95% CIs) for markers of bone formation also were assessed; bone-specific alkaline phosphatase (BSAP), 74% (67,80%), and osteocalcin, 29% (14,44%); marker of bone resorption deoxypyridinoline (DPD), 58% (52,64%); and measure of calcium homeostasis 24 h urine calcium, creatinine (Cr), 52% (41,61%). The magnitude of genetic influence differed with menopause for most variables. This study provides evidence for the importance of genetic factors in determining bone resorption and formation, calcium excretion, and the hormones regulating these processes. It shows for the first time a clear genetic effect on bone resorption in premenopausal women and the regulation of PTH, vitamin D metabolism, and calcium excretion. The genes controlling bone hormones and markers are likely to be useful therapeutic and diagnostic targets. [source] Genetic and environmental stability differs in reactive and proactive aggressionAGGRESSIVE BEHAVIOR, Issue 6 2009Catherine Tuvblad Abstract The aim of this study was to examine stability and change in genetic and environmental influences on reactive (impulsive and affective) and proactive (planned and instrumental) aggression from childhood to early adolescence. The sample was drawn from an ongoing longitudinal twin study of risk factors for antisocial behavior at the University of Southern California (USC). The twins were measured on two occasions: ages 9,10 years (N=1,241) and 11,14 years (N=874). Reactive and proactive aggressive behaviors were rated by parents. The stability in reactive aggression was due to genetic and nonshared environmental influences, whereas the continuity in proactive aggression was primarily genetically mediated. Change in both reactive and proactive aggression between the two occasions was mainly explained by nonshared environmental influences, although some evidence for new genetic variance at the second occasion was found for both forms of aggression. These results suggest that proactive and reactive aggression differ in their genetic and environmental stability, and provide further evidence for some distinction between reactive and proactive forms of aggression. Aggr. Behav. 35:437,452, 2009. © 2009 Wiley-Liss, Inc. [source] Body mass index, alcohol, tobacco and symptomatic gallstone disease: a Swedish twin studyJOURNAL OF INTERNAL MEDICINE, Issue 5 2007D. Katsika Abstract. Background/Aims., Both genetic and environmental factors are involved in the pathogenesis of gallstone disease (GD). We aimed to examine the association between symptomatic GD and overweight (body mass index, BMI, 25,30 kg m,2), obesity (BMI > 30 kg m,2), alcohol, smoking and smoke-free tobacco by analysing a large twin population. Methods., The Swedish Twin Registry (STR) was linked to the Swedish Hospital Discharge and Causes of Death Registries for GD and GD-surgery related diagnoses. Weight, height, use of alcohol, smoking and smoke-free tobacco were provided by STR and analysed for possible associations by conditional logistic regression. Results., Overweight and obesity were associated with a significantly higher risk for symptomatic GD in the whole study population (OR 1.86 and OR 3.38; CI: 1.52,2.28 and 2.28,5.02 respectively). High alcohol consumption was associated with a lower risk for GD in the whole population (OR 0.62; CI: 0.51,0.74) with no difference between discordant monozygotic and dizygotic twins (OR 1.08 and OR 0.96; CI: 0.82,1.42 and 0.79,1.16). Smoking or smoke-free tobacco was not correlated with GD. Conclusion., Consistent with epidemiological studies, we found positive associations between BMI and the development of symptomatic GD. High alcohol consumption was associated with a decreased risk against GD. Tobacco use has no impact on GD. [source] Neuroticism and Morning Cortisol Secretion: Both Heritable, But No Shared Genetic InfluencesJOURNAL OF PERSONALITY, Issue 5 2009Harriėtte Riese ABSTRACT Neuroticism is widely used as an explanatory concept in etiological research of psychopathology. To clarify what neuroticism actually represents, we investigated the phenotypic and genetic relationship between neuroticism and the morning cortisol secretion. In the current classic twin study, 125 female twin pairs (74 monozygotic and 51 dizygotic pairs) participated. For each participant, 4 different neuroticism scores were available to calculate a neuroticism composite score that was used in the statistical analyses. The morning cortisol secretion was assessed by 4 salivary samples in the 1st hour after awakening. Significant genetic influences for the neuroticism composite score (55%), and each of the 4 cortisol samples (52%,69%) were found. There was no phenotypic or genotypic relationship between neuroticism and morning cortisol secretion. Although neuroticism and cortisol were both heritable traits, they did not share any genetic influences. [source] The Role of Socioregional Factors in Moderating Genetic Influences on Early Adolescent Behavior Problems and Alcohol UseALCOHOLISM, Issue 10 2009Danielle M. Dick Background:, Twin and family studies have demonstrated that adolescent alcohol use and behavior problems are influenced by a combination of genetic and environmental factors. More recently, studies have begun to investigate how genetic and environmental influences may interact, with efforts underway to identify specific environmental variables that moderate the expression of genetic predispositions. Previously, we have reported that community-level factors, including urban/rural residency, migration rates, and prevalence of young adults, moderate the importance of genetic effects on alcohol use in late adolescence (ages 16 to 18). Here, we extend these findings to test for moderating effects of these socioregional factors on alcohol use and behavior problems assessed in a younger sample of adolescent Finnish twins. Methods:, Using data from the population-based Finnish twin study, FinnTwin12, biometric twin models were fit to data on >1,400 twin pairs to examine the significance of each of the socioregional moderating variables on alcohol use measured at age 14, and behavior problems, measured at age 12. Results:, We find no evidence of a moderating role of these socioregional variables on alcohol use; however, there was significant moderation of genetic influences on behavior problems, with effects limited to girls. Genetic influences assumed greater importance in urban settings, communities with greater migration, and communities with a higher percentage of slightly older adolescents. Conclusions:, The moderation effects observed on behavior problems in early adolescence paralleled the effects found on alcohol use late in adolescence in an independent sample, providing further support for the idea that behavior problems may represent an earlier manifestation of the predisposition to subsequent alcohol problems. Our findings also support the growing body of evidence suggesting that females may be more susceptible to a variety of environmental influences than males. [source] A behaviour-genetic analysis of orthographic learning, spelling and decodingJOURNAL OF RESEARCH IN READING, Issue 1 2008Brian Byrne As part of a longitudinal twin study of literacy and language, we conducted a behaviour-genetic analysis of orthographic learning, spelling and decoding in Grade 2 children (225 identical and 214 fraternal twin pairs) in the United States and Australia. Each variable showed significant genetic and unique environment influences. Multivariate analyses revealed very high genetic correlations among the variables, indicating that the same genes are involved in their aetiology. These genes are partly independent of those contributing to intelligence. A further analysis indicated that the covariation between decoding and orthographic learning is mediated by shared genes rather than by a direct causal path. The authors argue that a learning parameter, most directly assessed by orthographic learning in this study, underlies all three literacy variables. The results are also discussed in relation to Share's self-teaching hypothesis, which may require modification. [source] Influence of genetics on irritable bowel syndrome, gastro-oesophageal reflux and dyspepsia: a twin studyALIMENTARY PHARMACOLOGY & THERAPEUTICS, Issue 11 2007A. LEMBO Summary Background A genetic contribution has been proposed for irritable bowel syndrome (IBS) and gastro-oesophageal reflux disease (GERD), but is controversial. No twin data exist for dyspepsia. Aim To determine the relative contribution of genetic factors in GERD, dyspepsia (upper abdominal pain) and IBS. Methods A total of 986 twin pairs (from initial mail-out response 51%). Both members completed validated symptom and psychological questionnaires; 481 monozygotic pairs [mean (s.d.) age 53 ± 5.8 years] and 505 dizygotic pairs (mean age 54 ± 5.6 years). Results Prevalence of IBS, dyspepsia and GERD was 12%, 10% and 20%, respectively. Polychoric correlation for monozygotic twins for IBS (0.47) and GERD (0.44) were both substantially larger than those for dizygotic twins (0.17 and ,0.37, respectively). Polychoric correlation was slightly lower in monozygotic than dizygotic twins for dyspepsia. Genetic modelling confirmed the independent additive genetic effects in GERD and IBS but not dyspepsia. Estimates of genetic variance were 22% for IBS, 13% for GERD and 0% for dyspepsia, but adjusting for anxiety and depression removed the statistical significance for IBS and GERD. Conclusions There is a genetic contribution to GERD and IBS but not dyspepsia; this may be mediated by the hereditability of anxiety and depression. [source] Genetic and environmental influences on emotion-modulated startle reflex: A twin studyPSYCHOPHYSIOLOGY, Issue 1 2007Andrey P. Anokhin Abstract Emotion-modulated startle reflex is an important indicator of traitlike differences in affective processing implicated in the biological basis of personality and psychopathology. This study examined heritability of startle modulation by affective pictures in 66 pairs of monozygotic and 57 pairs of dizygotic female twins. Consistent with previous studies, startle magnitude was significantly influenced by emotional valence of the picture (positive A study of the occurrence of monochorionic and monozygotic twinning in the pigANIMAL GENETICS, Issue 1 2009D. Bjerre Summary In humans as well as in most farm animals, monozygotic twins have been described. Nevertheless, only a few reports of twinning in the pig have been published. It has been suggested that monozygotic twins are formed during the first 14 days of pregnancy. This monozygotic twin study includes the investigation of porcine monochorionic embryos from 76 sows at days 26,29 post-insemination (p.i.), as well as an examination of 10 whole litters at days 21,22 p.i. In the former group, 29% of the sows carried monochorionic embryos. Based on DNA profiling using microsatellite markers, one monozygotic twin pair was found among these embryos. In the latter group, three monozygotic twin pairs were identified. Thus, it can be concluded that although the occurrence of monozygotic twins in pigs is a sporadic event, the fusion of extra-embryonic membranes is relatively common. [source] Genetic and environmental influences on serum lipids and the effects of puberty: a Chinese twin studyACTA PAEDIATRICA, Issue 6 2009Tian-Jiao Chen Abstract Aim: To study the contribution of genes and environment on the variation of serum lipids and the effects of puberty. Methods: In total, 314 same-sex twin pairs aged 5,18 years were studied. Puberty was marked physiologically by spermarche/menarche, and model fitting was used to analyse the genetic and environmental variance and its difference before and after puberty. Results: Lipid levels were different before and after puberty. The genetic factor had an important influence on lipid levels; the heritability estimates of total cholesterol (TC), high-density lipoprotein (HDL), low-density lipoprotein (LDL), lipoprotein(a) (Lp(a)) and apolipoprotein E (ApoE) were between 49 and 86%. The total phenotypic variances of TC, HDL, LDL, Lp(a) and ApoE decreased after puberty, mainly as a result of decrease of genetic variance, even though the common environmental variance for HDL, Lp(a) and ApoE increased. Conclusion: Genes and the environment have different effects on the levels of different lipids. The shared environmental effects on lipids are very important in children. The role of puberty on lipids deserves future study. [source]
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