Male Twin Pairs Research Articles

Co-occurrence of abuse of different drugs in men: the role of drug-specific and shared vulnerabilities.

Previous research has demonstrated genetic and environmental influences on abuse of individual substances, but there is less known about how these factors may influence the co-occurrence of abuse of different illicit drugs. We studied 3372 male twin pairs from the Vietnam Era Twin Registry. They were interviewed using the Diagnostic Interview Schedule, Version III, Revised to investigate the extent to which the abuse of different categories of drugs occurs together within an individual, as well as the possibility that genetic and environmental factors are responsible for observed co-occurrence. Co-occurrence was quantified using odds ratios and conditional probabilities. Multivariate biometrical modeling analyses were used to assess genetic and environmental influences on co-occurrence. Abusing any category of drug was associated with a marked increase in the probability of abusing every other category of drugs. We found evidence for a shared or common vulnerability factor that underlies the abuse of marijuana, sedatives, stimulants, heroin or opiates, and psychedelics. This shared vulnerability is influenced by genetic, family environmental, and nonfamily environmental factors, but not every drug is influenced to the same extent by the shared vulnerability factor. Marijuana, more than other drugs, was influenced by family environmental factors. Each category of drug, except psychedelics, had genetic influences unique to itself (ie, not shared with other drug categories). Heroin had larger genetic influences unique to itself than did any other drug. There are genetically and environmentally determined characteristics that comprise a shared or common vulnerability to abuse a range of illicit drugs.

From the research on electrophoretical mobility of nuclei in twins.

I studied 8 pairs of male twins and 14 pairs of female twins. The aim of this paper is to demonstrate the evaluation of development age in pairs of twins examined through the electrophoretical mobility of nuclei. EMN index in pairs of male twins, the index figures do not change dramatically between the ages of 8-12. EMN index in pairs of female twins rises from 9-year-old to 11-year-old pair. In this paper I want to indicate the studies on development age, which began at The Twins Festival in Szczecin in 1998.

The effect of lifelong exercise on psychomotor reaction time: a study of 38 pairs of male monozygotic twins

The effect of lifelong exercise on psychomotor reaction time: a study of 38 pairs of male monozygotic twins. Med. Sci. Sports Exerc., Vol. 30, No. 9, pp. 1445-1450, 1998. Purpose: The aim was to study the effect of lifetime physical activity on psychomotor speed. Methods: Foot and dominant hand visual simple and choice psychomotor reaction times were studied among monozygotic twins (38 pairs) aged 35-69, discordant for lifetime exercise histories. Results: There was a trend that some components of psychomotor reaction time were faster for frequent than for occasional exercisers, but the findings were not consistent for the hand and feet. After controlling for occupational physical activity, only choice decision time for the hand (26 ms, P < 0.01) and choice reaction time for the contralateral foot (51 ms, P < 0.05) both remained 7% faster. There was no trend for systematic differences in reaction times between twins engaged in regular exercise versus their siblings exercising infrequently. Conclusions: Results suggest a somewhat smaller effect of exercise than reported in previous studies. Reaction time may be significantly affected only by vigorous, frequent exercise. Thus, health promotion through exercise may be unlikely to have notable effects on reaction time.

The effect of lifelong exercise on psychomotor reaction time: a study of 38 pairs of male monozygotic twins.

The aim was to study the effect of lifetime physical activity on psychomotor speed. Foot and dominant hand visual simple and choice psychomotor reaction times were studied among monozygotic twins (38 pairs) aged 35-69, discordant for lifetime exercise histories. There was a trend that some components of psychomotor reaction time were faster for frequent than for occasional exercisers, but the findings were not consistent for the hand and feet. After controlling for occupational physical activity, only choice decision time for the hand (26 ms, P < 0.01) and choice reaction time for the contralateral foot (51 ms, P < 0.05) both remained 7% faster. There was no trend for systematic differences in reaction times between twins engaged in regular exercise versus their siblings exercising infrequently. Results suggest a somewhat smaller effect of exercise than reported in previous studies. Reaction time may be significantly affected only by vigorous, frequent exercise. Thus, health promotion through exercise may be unlikely to have notable effects on reaction time.

Identical de novo mutation at the D4F104S1 locus in monozygotic male twins affected by facioscapulohumeral muscular dystrophy (FSHD) with different clinical expression.

Facioscapulohumeral muscular dystrophy (FSHD) is a progressive hereditary neuromuscular disorder, transmitted in an autosomal dominant fashion. Its clinical expression is highly variable, ranging from almost asymptomatic subjects to wheelchair dependent...

How heritable is individual susceptibility to death? The results of an analysis of survival data on Danish, Swedish and Finnish twins

AbstractMolecular epidemiological studies confirm a substantial contribution of individual genes to variability in susceptibility to disease and death for humans. To evaluate the contribution of all genes to susceptibility and to estimate individual survival characteristics, survival data on related individuals (eg twins or other relatives) are needed. Correlated gamma-frailty models of bivariate survival are used in a joint analysis of survival data on more than 31 000 pairs of Danish, Swedish and Finnish male and female twins using the maximum likelihood method. Additive decomposition of frailty into genetic and environmental components is used to estimate heritability in frailty. The estimate of the standard deviation of frailty from the pooled data is about 1.5. The hypothesis that variance in frailty and correlations of frailty for twins are similar in the data from all three countries is accepted. The estimate of narrow-sense heritability in frailty is about 0.5. The age trajectories of individual hazards are evaluated for all three populations of twins and both sexes. The results of our analysis confirm the presence of genetic infiuences on individual frailty and longevity. They also suggest that the mechanism of these genetic infiuences may be similar for the three Scandinavian countries. Furthermore, results indicate that the increase in individual hazard with age is more rapid than predicted by traditional demographic life tables.

Common genetic risk factors for conduct disorder and alcohol dependence.

The association between retrospectively reported childhood conduct disorder (CD) and a history of alcohol dependence (AD) was examined in a sample of 2,682 male, female, and unlike-sex adult twin pairs. There was a strong association between CD and AD in both men (tetrachoric r = .34, odds ratio = 2.8) and women (tetrachoric r = .53, odds ratio = 9.9). Genetic factors accounted for most of the association between CD and AD liability in men and women, with the remainder of the association being due to nonshared individual-specific environmental factors. Genetic influences common to CD and AD accounted for 17% and 35% of the genetic variation in AD liability in men and women, respectively, and accounted for 11% and 23% of the total variation in AD liability in men and women, respectively. The results suggest that there are common genetic risk factors for CD and AD or that CD itself is an important genetically influenced risk factor for AD.

A tooth per child?

same social status but who had different numbers of children and who fell into different dental categories. In 28 of these pairs, the twin with more children had fewer teeth (p<0·001). No such relationship was found for male twin pairs. In historic and prehistoric populations, caries and loss of teeth increased the risk of death. The long-term costs of childbearing on women’s health may have been substantial and they may still be significant.

Latent class analysis of temperance board registrations in Swedish male-male twin pairs born 1902 to 1949: searching for subtypes of alcoholism.

Alcoholism is clinically heterogeneous. We have attempted to identify and validate subtypes of broadly defined alcoholism. Latent class analysis (LCA) was applied to data on the number, age at onset and reasons for temperance board registration (TBR) in all male-male twin pairs of known zygosity born in Sweden from 1902-1949. Of the five classes identified, two were relatively common: single-cause registrant-drunk (SCR-D); and early-onset multiple-cause registrant (EO-MCR). In contrast to the SCR-D class, the EO-MCR class was characterized by: (i) earlier age at first TBR; (ii) higher number of TBRs; (iii) TBRs for drunk driving and alcohol-related crimes; (iv) much higher risk for alcohol-related imprisonment and hospitalization; (v) higher levels of neuroticism and novelty-seeking; and (vi) much greater risk for TBR in co-twins. In twin pairs concordant for TBR, concordance for LCA-derived class assignment far exceeded chance expectation, more so in monozygotic than in dizygotic pairs. Alcoholism is aetiologically as well as clinically heterogeneous. The two most common subtypes identified in these analyses bear substantial but imperfect resemblance to previously proposed typologies.

Determinants of psychomotor speed among 61 pairs of adult male monozygotic twins.

Declining psychomotor speed is an indicator of the aging process, and it is influenced by genetics and environmental factors. The present study examined the relative effects of familial aggregation (reflecting a combination of genetics and early environmental influences), and occupational, lifestyle, and health factors on psychomotor speed. Hand and foot psychomotor speed was studied with 61 pairs of monozygotic male twins aged 35-67 years from the population-based Finnish Twin Cohort. The determinants of visual simple and choice reaction times were analyzed with multiple regression analysis. Familial aggregation, reflecting genetic influences and shared environmental effects, explained in mean 47% of decision times, 31% of movement times, and 37% of response times (decision time and movement time combined). Age, cardiovascular morbidity, lifetime vigorous and frequent exercise participation, and mean lifetime daily hours sitting at work explained 0-19% of hand psychomotor speed and 0-10% of foot speed, depending on the outcome. The predicted increase in decision times due to the presence of cardiovascular morbidity was 11-35 ms. The predicted increase for hand and contralateral foot response times between ages 45 and 55 was 18-41 ms. Smaller effects were noted for each year of strenuous exercise and each hour/day of average lifetime sitting at work. Results indicate that cardiovascular status, age, strenuous exercise, and work play a role in psychomotor speed, but a rather minor one. In contrast, genetic and shared early environmental influences as revealed from familial aggregation were relatively strong, yet a major proportion of the variability in psychomotor speed remained unexplained.

The Ser447–Ter mutation of the lipoprotein lipase gene relates to variability of serum lipid and lipoprotein levels in monozygotic twins

Studies on monozygotic twins support a role for genetic determinants of plasma lipid, lipoprotein, and apolipoprotein levels. Gene variants of the enzyme lipoprotein lipase have been shown to associate with dyslipidemia and coronary artery disease. We assessed the gene–environment interaction by investigating the relationship between the lipoprotein lipase gene and plasma lipid, lipoprotein, and apolipoprotein variability and levels among 54 male monozygotic twin pairs (aged 18–28 years). The Ser447–Ter mutation (C→G transversion) was associated with significantly smaller within-pair differences in plasma high density lipoprotein-cholesterol (CG [n = 10] vs. CC [n = 44], 3.7 ± 5.3 mg/dl vs. 6.4 ± 5.2 mg/dl, P < 0.03) and total cholesterol (CG [n = 10] vs. CC [n = 44], 7.9 ± 9.4 mg/dl vs. 15.8 ± 12.7 mg/dl, P < 0.05), indicating attenuated variability in response to environmental stimuli. This observation of a restrictive variability gene effect further supports a role for the lipoprotein lipase gene in the genetic regulation of lipids and lipoproteins and suggests that the Ser447–Ter mutation exerts multiple effects. This study also raises the possibility of a genetically determined responsiveness to dyslipidemia therapies.—Thorn, J. A., E. W. A. Needham, R. K. Mattu, J. Stocks, and D. J. Galton. The Ser447–Ter mutation of the lipoprotein lipase gene relates to variability of serum lipid and lipoprotein levels in monozygotic twins.

Heritability of ECG measurements in adult male twins

To assess the genetic contribution to electrocardiographic (ECG) measurements, heritability analysis was performed on ECG data collected on 251 pairs of adult male twins during the second examination of the National Heart, Lung and Blood Institute twin study, a multicenter study of cardiovascular risk factors. Resting 12-lead ECGs were obatained on each twin, pair and, the R-R, QRS, QT, and JT intervals were measured. Both the R-R and QT intervals demonstrated significant heritable components, accounting for 77% and 36%, respectively, of the variability. No significant heritable component of the QRS complex could be identified. Although the MZ intraclass correlation was higher than the DZ intraclass correlation, the JT interval did not demonstrate significant heritability. Therefore, in adult males both heart rate and the duration of ventricular repolarization have significant heritable components. These heritable components may need to be considered when using ECG measurements to screen for patients at risk for cardiovascular disorders or sudden cardiac death.

Common genetic risk factors for conduct disorder and alcohol dependence.

The association between retrospectively reported childhood conduct disorder (CD) and a history of alcohol dependence (AD) was examined in a sample of 2,682 male, female, and unlike-sex adult twin pairs. There was a strong association between CD and AD in both men (tetrachoric r = .34, odds ratio = 2.8) and women (tetrachoric r = .53, odds ratio = 9.9). Genetic factors accounted for most of the association between CD and AD liability in men and women, with the remainder of the association being due to nonshared individual-specific environmental factors. Genetic influences common to CD and AD accounted for 17% and 35% of the genetic variation in AD liability in men and women, respectively, and accounted for 11% and 23% of the total variation in AD liability in men and women, respectively. The results suggest that there are common genetic risk factors for CD and AD or that CD itself is an important genetically influenced risk factor for AD.

Genetic and environmental influences on EEG coherence.

EEG coherence measures the covariation in electrical brain activity between two locations on the scalp and is used to study connectivity between cortical regions. The aim of this study was to determine the heritability of EEG coherence. Coherence was measured in a group of 213 16-yr-old twin pairs. By including male and female twin pairs in the sample, sex differences in genetic architecture were systematically examined. The EEG was obtained during quiet supine resting. Coherence was estimated for short and long distance combinations of electrode pairs along the anterior-posterior axis within a hemisphere for four frequency bands (delta, theta, alpha and beta). Averaged over all electrode combinations about 60% of the variance was explained by genetic factors for coherence in the theta, alpha and beta bands. For the delta band, the heritability was somewhat lower. No systematic sex differences in genetic architecture were found. All environmental influences were nonshared, i.e., unique factors including measurement error. Environmental factors shared by twin siblings did not influence variation in EEG coherence. These results suggest that individual differences in coherence form a potential candidate for (molecular) genetic studies on brain function.

Sibling interactions, self-regulation, and cynical hostility in adult male twins.

Chronic hostility is associated with increased vulnerability to serious physical illness, making developmental influences on this trait important. We used the Structural Analysis of Social Behavior (SASB) model to examine retrospective descriptions of twin interactions during childhood in a sample of 48 adult male twin pairs. Consistent with previous research on parental behavior correlates, self-reported hostility as measured by the Cook and Medley Ho scale was associated with descriptions of the twin's behavior as hostile, controlling, and neglecting. Consistent with the SASB principle of introjection, hostility was also associated with self directed hostility and neglect. Thus, a developmental perspective not only describes possible social contexts involved in the emergence of this trait, but also suggests possible psychological underpinnings. Implications for models of hostility and health are discussed.

Determinants of isokinetic and psychophysical lifting strength and static back muscle endurance: a study of male monozygotic twins.

Retrospective cohort. To determine the relative contributions of anthropometric factors, physical activity, back and neck pain, overall health, and familial aggregation (the combined effects of genetics and childhood environment) to different measurements of adult back muscle function. Many methods of muscle testing are employed in the attempt to predict, prevent, treat, and rehabilitate low back pain. Poor correlations between the test results suggest that they are measuring different attributes and have different determinants. Muscle function tests, magnetic resonance images, and a detailed interview were obtained in 65 pairs of monozygotic male twins. Familial aggregation was the strongest determinant of isokinetic and psychophysical lifting and static back endurance, explaining 56%, 32%, and 15% of the variances, respectively, beyond that which age alone predicted. Back pain and physical loading in work and leisure explained 2%, 0%, and 23% of the variances. The combined effects of genetics and childhood environment play a dominant role in determining adult back muscle function. Physical loading at work and leisure, back and neck pain history, overall health, and anthropometric factors had a comparatively minor role, suggesting that the potential of interventions to increase and sustain back muscle function in healthy adults, measured through these tests, may be limited. The relative contributions of constitutional, behavioral, and environmental factors differ substantially in the three tests, and provide insights into what these commonly used tests actually reflect or measure. This knowledge can be used to guide more appropriate selection and interpretation of results of back muscle function tests.

Effect of high-fat and low-fat diets on voluntary energy intake and substrate oxidation: studies in identical twins consuming diets matched for energy density, fiber, and palatability

There remains controversy over the effects of dietary fat content on voluntary energy intake. Additionally, the question of whether there is a genetic susceptibility to overeating high-fat diets has not been resolved. To address these issues, we designed two diets: a low-fat diet providing approximately 20% of energy as fat and a high-fat diet with approximately 40% of energy as fat. The diets were matched for energy density, fiber, and palatability. In a two-phase, 18-d intervention study, voluntary energy intakes and macronutrient oxidation rates during the fasting and fed states were determined in seven pairs of identical male twins. In contrast with results of previous intervention studies, in which low-fat and high-fat diets were not matched for energy density and other associated variables, we observed no significant difference in voluntary energy intake between the low-fat and high-fat phases, and mean daily intakes were similar (10.3 and 10.7 MJ/d, respectively). Postprandial rates of fat oxidation tended to reflect fat intakes in the two dietary phases, thus helping to explain the lack of a difference in mean energy intakes. There was also a significant twin-pair similarity in differences in energy intakes between dietary phases (P = 0.013). These results suggest that dietary fat content does not have a major influence on voluntary energy intake when dietary variables usually associated with fat are controlled for and that there may be a familial influence on the effects of dietary fat content on energy intake.

Abstract

Studies on monozygotic twins support a role for genetic determinants of plasma lipid, lipoprotein, and apolipoprotein levels. Gene variants of the enzyme lipoprotein lipase have been shown to associate with dyslipidemia and coronary artery disease. We assessed the gene-environment interaction by investigating the relationship between the lipoprotein lipase gene and plasma lipid, lipoprotein, and apolipoprotein variability and levels among 54 male monozygotic twin pairs (aged 18-28 years). The Ser447-Ter mutation (C-->G transversion) was associated with significantly smaller within-pair differences in plasma high density lipoprotein-cholesterol (CG [n = 10] vs. CC [n = 44], 3.7+/-5.3 mg/dl vs. 6.4+/-5.2 mg/dl, P < 0.03) and total cholesterol (CG [n = 10] vs. CC [n = 44], 7.9+/-9.4 mg/dl vs. 15.8+/-12.7 mg/dl, P < 0.05), indicating attenuated variability in response to environmental stimuli. This observation of a restrictive variability gene effect further supports a role for the lipoprotein lipase gene in the genetic regulation of lipids and lipoproteins and suggests that the Ser447-Ter mutation exerts multiple effects. This study also raises the possibility of a genetically determined responsiveness to dyslipidemia therapies.

Genetic determinants of regional fat distribution.

Upper body fat and abdominal visceral fat are two obesity-related phenotypes of interest because of their relationships with a variety of metabolic complications. The heritability of the amount of upper body fat or the level of upper body fat relative to lower body fat ranges from approximately 30-50% of the phenotype's age, sex and total body fat adjusted variance. On the other hand, familial studies of abdominal visceral fat reveal that the familial transmission reaches > 50% of the age, sex and total body fat adjusted variance. Complex segregation analysis undertaken with a panel of nuclear families indicates that major genes may account for a significant fraction of the variance in upper body fat and abdominal visceral fat. Two intervention studies conducted with pairs of male identical twins have shown that changes in upper body fat and visceral fat are more similar within pairs than between pairs, either in phenotype increments when challenged by chronic overfeeding, or in adipose tissue losses after exposure to long-term negative energy balance conditions. The evidence accumulated to date is sufficient to justify undertaking a search for the specific genes and molecular markers involved in the heterogeneity commonly observed in human fat topography.

Emotional modulation of the startle reflex in twins: preliminary findings

This study investigated twin similarity in general startle reflex reactivity and emotional modulation. Seventeen monozygotic (MZ) and 12 dizygotic (DZ) male twin pairs received startling acoustic stimuli while viewing emotionally positive, negative and neutral slides. Electromyographic (EMG) responses were recorded from the orbicularis oculi. Members of MZ twin pairs had similar response amplitudes under all three valence conditions. In addition, modulation scores for the positive and negative conditions, representing the percent change in response amplitude between the affective and the neutral conditions, also showed significant similarity within MZ twin pairs. Overall, members of DZ twin pairs were not found to be significantly similar on any of the measures. These preliminary findings suggest that emotional modulation of the startle reflex shows familial resemblance within MZ pairs. Given the lack of resemblance between DZ twins, it is tentatively suggested that affective modulation may be under partial genetic control.