Pairs Of Male Monozygotic Twins Research Articles

A twin study of the association of post-traumatic stress disorder and combat exposure with long-term socioeconomic status in Vietnam veterans.

This study examines the association between post-traumatic stress disorder (PTSD) and combat exposure with the socioeconomic status of 2210 male monozygotic veteran twin pairs in 1987. In the unadjusted analysis on individuals, modest correlations indicated that those with PTSD were more likely to have been divorced, and less likely to be currently employed or to achieve high status in income, education or occupation. In the crude analysis of veterans not suffering from PTSD, there were small positive correlations between combat level experienced and the likelihood of ever being married, ever being divorced, and the number of years employed at the current job. However, when we examined identical twins discordant for PTSD, and adjusted for pre-military and military service factors, only unemployment remained significant. Likewise, in combat-discordant twins, no significant effects on the socioeconomic indicators were seen. We conclude that PTSD and combat experience in Southeast Asia have not had a major impact on the socioeconomic status of veterans.

Genetic influences on job satisfaction and work values

Two replications of the Arvey, Bouchard, Segal and Abraham (1989; Journal of Applied Psychology, 74, 187–192) study were conducted investigating whether there is a significant genetic association with general job satisfaction as well as its facets. A sample of male monozygotic ( n = 95) and dizygotic ( n = 80) twin pairs reared together completed the Minnesota Satisfaction Questionnaire. As in Arvey et al. (1989), a significant genetic influence was demonstrated for Intrinsic Satisfaction with no support given for genetic influence on Extrinsic Satisfaction. Only modest support was given for a genetic influence on General Satisfaction. A second study using a sample of 1236 monozygotic and 1165 dizygotic twin pairs reared together showed a significant genetic influence on overall job satisfaction to replicate the Arvey et al. (1989) study as well as evidence for the genetic influence on work values to replicate the Keller Bouchard, Arvey, Segal and Dawis (1992) study.

The impact of cigarette and alcohol consumption on weight and obesity. An analysis of 1911 monozygotic male twin pairs

The impact of cigarette and alcohol consumption on weight and obesity. An analysis of 1911 monozygotic male twin pairs

Hostility and Nonshared Family Environment: A Study of Monozygotic Twins

A sample of 25 adult male monozygotic (Mz) twin pairs completed the Cook and Medley Hostility scale, and Structural Analysis of Social Behavior measures of their parents′ behavior toward them during childhood. Results indicated that high levels of hostile control and low levels of positive involvement from parents were associated with high levels of self-reported hostility. To rule out possible genetic influences on this covariation between parental behavior and hostility, co-twin difference scores for hostility and parental behavior were computed and correlated. The more hostile Mz co-twin described his parents as exhibiting a greater degree of hostile control. Thus, nongenetic variance in hostility was associated with perceived differences in early environments. Implications for the development of hostility and its association with health are discussed.

Sexual orientation, sexual identity, and sex-dimorphic behaviors in male twins

Sexual orientation, sexual identity, and sex-dimorphic behaviors were assessed concurrently and retrospectively, for childhood, in 95 pairs of male monozygotic (MZ) twins and 63 pairs of dizygotic (DZ) twins. There was a significantly higher rate of adult homosexuality among the MZ than among DZ twins. We employed a model-fitting approach using LISREL to test for genetic and environmental influences on variation for each trait singly and on the covariation among all six traits (three for childhood and three for adulthood). Univariate analyses confirmed the presence of familial factors for five of the six variables but were generally unable to distinguish shared environmental from genetic influences. Hierarchical tests of multivariate models supported the existence of an additive genetic factor contributing to the covariance among the variables. More restrictive multivariate models yielded a significant genetic influence on sexual orientation. Because of the different rates of orientation by zygosity and because of the restrictive nature of some of the multivariate models, our results are best considered tentative but do suggest that further biometrically oriented studies of sexual orientation and its correlates would be worthwhile.

A Delusional Disorder That Occurred in One of a Pair of Monozygotic Twins

The authors reported a pair of male monozygotic twins in one of whom a delusional disorder occurred, and discussed the etiology of that disorder. The analysis of the twins indicates the following: 1. The disposition for the delusional disorder might be related to a psychological tendency to experience a delusion that might be based on a genetic factor. This might be strengthened by the development of a hypersensitive personality (Kretschmer, E.) promoted by environmental factors. 2. A hypersensitive personality might be a significant risk factor for the delusional disorder.

Dietary calcium and bone mineral density in men

We have observed that familial factors have a decided influence on the plasma content of sex steroids in men both in the general population and in men of families with prostatic cancer. The contribution of genetic and nongenetic familial factors on the variation of plasma sex steroid content and action has now been investigated in 75 pairs of normal male monozygotic (MZ) twins and 88 pairs of dizygotic (DZ) twins. Zygosity was determined by measuring ten blood proteins and enzymes. The mean plasma values for testosterone (T), dihydrotestosterone (DHT), estradiol (E2), estrone (E1), and 3α-androstanediol glucuronide (3α-diol G), free T, LH, FSH, SHBG, age, and degree of adiposity were all similar between the groups of twins. Familial factors (P < 0.01) accounted for 50% or more of the variation in plasma hormone levels in MZ twins (3α-diol G, 84%; TDHT, 70%; T, 63%; E1, 63%; free T, 61%; E2, 57%; DHT, 56%; LH, 55%; and FSH, 54%) except for SHBG, which was 30%. The familial influence was greater in MZ twins than in DZ twins for all measurements except for SHBG. The heritability of the variation of hormone levels in plasma was determined from the equation: 2[rMZ(intraclass correlation) - rDZ]. Genes regulate 25% to 76% of the total variation of plasma content of the hormones except for DHT (12%) and SHBG (<1%). Genetic regulation of tissue DHT formation was suggested by observing a 48% genetic effect on the plasma content of 3α-diol G. These observations suggest that genetic factors make major contributions in regulating estrogen and testosterone levels and tissue DHT production in normal men.

Clinicoelectrographic Concordance Between Monozygotic Twins with Severe Myoclonic Epilepsy in Infancy

Clinical features of a pair of monozygotic male twins, both with severe myoclonic epilepsy in infancy (SME), are described. They were almost completely concordant with respect to seizure onset, clinical seizure symptomatology, interictal, and ictal EEG expressions and seizure prognosis. The existence of such twins suggests the possibility that a genetic factor is determinant in the etiology of this particular epileptic syndrome.

The Response to Long-Term Overfeeding in Identical Twins

We undertook this study to determine whether there are differences in the responses of different persons to long-term overfeeding and to assess the possibility that genotypes are involved in such differences. After a two-week base-line period, 12 pairs of young adult male monozygotic twins were overfed by 4.2 MJ (1000 kcal) per day, 6 days a week, for a total of 84 days during a 100-day period. The total excess amount each man consumed was 353 MJ (84,000 kcal). During overfeeding, individual changes in body composition and topography of fat deposition varied considerably. The mean weight gain was 8.1 kg, but the range was 4.3 to 13.3 kg. The similarity within each pair in the response to overfeeding was significant (P less than 0.05) with respect to body weight, percentage of fat, fat mass, and estimated subcutaneous fat, with about three times more variance among pairs than within pairs (r approximately 0.5). After adjustment for the gains in fat mass, the within-pair similarity was particularly evident with respect to the changes in regional fat distribution and amount of abdominal visceral fat (P less than 0.01), with about six times as much variance among pairs as within pairs (r approximately 0.7). We conclude that the most likely explanation for the intrapair similarity in the adaptation to long-term overfeeding and for the variations in weight gain and fat distribution among the pairs of twins is that genetic factors are involved. These may govern the tendency to store energy as either fat or lean tissue and the various determinants of the resting expenditure of energy.

Decreased beta-adrenergic receptor density and catecholamine response in male cigarette smokers. A study of monozygotic twin pairs discordant for smoking.

The effect of long-term cigarette smoking on beta-adrenoceptor density and catecholamine response was studied in 10 monozygotic male twin-pairs discordant for smoking, with an average discordance time for smoking of 23 years (range, 12-35 years). The density of beta-adrenergic receptors was 40% lower in the lymphocytes of smoking twins compared with their nonsmoking cotwins (beta-receptor density, 6.7 +/- 1.2 and 11.1 +/- 1.8 fmol/10(6) cells, respectively; p less than 0.05). The corresponding apparent Kd values were 31.7 +/- 5.5 and 26.7 +/- 5.4 pM, respectively. Stimulation of the lymphocyte beta-receptors resulted in significantly lower levels of cyclic adenosine monophosphate in the smokers compared with the nonsmokers (16.2 +/- 3.3 vs. 29.2 +/- 6.5 pmol/10(6) cells, p less than 0.05). When subjected to submaximal exercise, the smokers had a lower level of cyclic adenosine monophosphate in plasma (25.9 +/- 1.2 vs. 28.6 +/- 1.0, p less than 0.05) and a net decrease was seen in plasma free fatty acids in the smokers compared with a net increase in the nonsmokers (-15% vs. +19%, p less than 0.01). The total plasma catecholamine level was, in the basal state, significantly higher in smokers compared with nonsmokers (74.8%, p less than 0.05). The intrapair difference in plasma norepinephrine predicted well the intrapair difference in beta-receptor density (r = -0.84, p less than 0.001). We conclude that the autonomic neurohumoral response evoked by cigarette smoking results in downregulation of beta-adrenergic receptors in long-term smokers.

Enhanced activation of the renin-angiotensin-aldosterone system in chronic cigarette smokers: a study of monozygotic twin pairs discordant for smoking.

Plasma renin activity (PRA) and aldosterone concentration were measured before and during submaximal exercise in 10 male monozygotic twin pairs who were discordant for smoking. In nine twin pairs PRA was higher in the smoker both at rest and during exercise. The mean PRA was 99% higher at rest and 84% higher during exercise than in nonsmokers. Plasma aldosterone levels were higher at rest in seven smokers and during exercise in eight smokers compared with the respective nonsmokers. The mean aldosterone level at rest was 23% and during exercise 40% higher in the smokers than in the nonsmokers. Chronic smoking induces increased PRA, which results in increased aldosterone formation, presumably via enhanced generation of angiotensin II. This may partly explain the greater vasoconstrictive reactivity typical of the arteries of chronic smokers.

Heredity and changes in plasma lipids and lipoproteins after short-term exercise training in men.

The aims of this controlled experiment were to investigate the effects of short-term aerobic exercise training on plasma lipid and lipoprotein concentrations and the role of heredity in determining the individual variation observed in the lipoprotein-lipid response. Six pairs of male monozygotic (MZ) twins were subjected to an exercise training program that induced a 22,000 kcal energy deficit after 22 consecutive days of training. This program significantly reduced body weight, percent body fat, and subcutaneous fat and significantly increased maximal oxygen consumption (VO2max) (p less than 0.005). The plasma insulin response to an oral glucose challenge was markedly reduced after training (p less than 0.001). Plasma triglyceride concentration decreased and the high density lipoprotein cholesterol (HDL-CHOL)/CHOL ratio increased with training (p less than 0.05). Subjects also displayed substantial individual variation in their response to exercise training, but the changes in plasma CHOL, apolipoprotein (apo) B low density lipoprotein cholesterol (LDL-CHOL), HDL-CHOL, and the HDL-CHOL/CHOL ratio tended to be similar within MZ twin pairs (0.67 less than or equal to ri less than or equal to 0.92; 0.05 greater than p less than 0.0001) thus indicating a significant effect of heredity on the sensitivity of plasma lipids and lipoproteins to exercise training.(ABSTRACT TRUNCATED AT 250 WORDS)

Physical exercise provokes platelet desensitization in men who smoke cigarettes - involvement of sympathoadrenergic mechanisms - a study of monozygotic twin pairs discordant for smoking

Since chronic smoking is known to be a dominant risk factor for morbidity and mortality in cardiovascular diseases related to enhanced atherogenesis and arterial thrombogenesis, the mechanisms causing these effects are of interest. The present study aims to assess the basic biochemical and haemorheological parameters among male monozygotic twinpairs, who have been discordant for smoking in average for over 20 years. Because smoking is known to cause enhanced sympathoadrenergic activation, the study was designed to further stimulate this by means of physical exercise. The platelet aggregation in vitro and serum-thromboxane B 2 (S-TxB 2) did not differ at rest, but after exercise smokers′ platelets were desensitized to all doses of adrenaline and low doses of ADP as well as collagen and the levels of S-TxB 2 were lower than among nonsmokers. This finding was supported by the decreased release of serotonin and TxB 2 during aggregation induced with adrenaline. The leucocyte counts were significantly higher among smokers at rest and haematocrit as well as platelet counts showed the same tendency. Fibrinogen tended to be be elevated among smokers after exercise and together with haematocrit levels implicated increased blood viscosity. FVIII, vWF and β-thromboglobulin did not differ. In conclusion we suggest that in smokers the significant exhaustion of platelets to in vitro stimulation might be a consequence of continuous platelet activation during physical stress. This phenomenon together with our other findings implies that the sympathoadrenergic system has a multiple role in vivo, which needs further research to elucidate the mechanisms involved in the effects of smoking on cardiovascular diseases.

Lifestyle and blood pressure levels in male twins in Utah.

Healthy male monozygotic (MZ) and dizygotic (DZ) twin pairs (MZ pairs = 77; DZ pairs = 88) were studied to assess the effect of dietary intake, physical activity, physical fitness, body mass index (BMI), sum of the triceps and subscapular skinfold measurements, alcohol and caffeine consumption, and smoking patterns on blood pressure. Data on physical activity, detailed dietary intake, medical history, and demographics were obtained from a questionnaire. A bicycle ergometer was used to estimate level of fitness; other medical information was ascertained from physical examination. After normalizing the study variables, intraclass correlations for BMI and the sum of the triceps and subscapular skinfold measurements were higher in MZ than in DZ twin pairs (BMI: MZ r = 0.76, DZ r = 0.48; skinfolds: MZ r = 0.73, DZ r = 0.28), as were VO2max(MZ r = 0.63, DZ r = 0.25) and post-bike heart rate (MZ r = 0.69, DZ r = 0.19). Both systolic (SBP) and diastolic blood pressure (DBP) had high heritability estimates (SBP = 0.60, and DBP = 0.66). Using factor analysis, four major lifestyle factors were identified and categorized as: 1) dietary intake; 2) a factor heavily weighted by cigarette smoking, alcohol and caffeine consumption; 3) fatness; 4) physical activity and physical fitness. Adjustment for these factors did not alter heritability estimates for either SBP or DBP.

Genotype-influenced changes in serum HDL cholesterol after short-term overfeeding in man: Association with plasma insulin and triglyceride levels

Six pairs of male monozygotic (MZ) twins were submitted to a 22-day overfeeding period during which they ingested a daily surplus of 1,000 kcal above their individual daily energy needs in the form of a mixed diet. Serum lipids, lipoproteins, and apoprotein A and B concentrations were measured before and after the overfeeding period. Percentage of body fat, fasting plasma glucose, and insulin levels as well as plasma glucose and insulin concentrations after a glucose challenge were also measured before and after overfeeding. Results showed that before overfeeding, MZ twins exhibited a significant intrapair resemblance for total serum cholesterol (CHOL), triglycerides (TG), low density lipoprotein cholesterol (LDL-C), and for the high density lipoprotein-cholesterol/total cholesterol ratio ( HDL-C CHOL ) (8.2 ≦ F ratios ≦ 32.7, P < .01). The overfeeding experiment induced significant increases only in serum CHOL ( P < .01) and in serum LDL-C ( P < .05). However, although mean group values of serum TG, HDL-C, and HDL-C CHOL ratio were not significantly modified by overfeeding, there were large interindividual variations in the response of these variables to the experiment. Results suggest that changes in serum TG, HDL-C, and in the HDL-C CHOL ratio were significantly associated with the genotype of the subjects as a significant intrapair resemblance in the response to overfeeding was observed for these variables (0.69 ≦ r ≦ .85, P < .05). Moreover, individual changes in serum HDL-C and in HDL-C CHOL ratio were negatively correlated with changes in serum TG ( r = −.64, P < .05 and r = −.84, P < .01; respectively). Finally, subjects that showed an increase in serum TG levels during overfeeding also demonstrated elevated fasting plasma insulin concentrations ( r = .67, P < .05) and increased plasma insulin levels during an oral glucose challenge ( r = .68; P < .05). These results suggest that the genotype may determine the sensitivity to develop hypertriglyceridemia and a potentially atherogenic lipoprotein-lipid profile (reduced HDL-C CHOL ratio) following a short-term caloric excess. These results also suggest that heredity plays a role in the interindividual variation observed in plasma lipoproteins when chronically overfed.

Is the response of plasma glucose and insulin to short-term exercise-training genetically determined?

Six male monozygotic (MZ) twin pairs participated in the present study which was undertaken to assess the contribution of heredity to changes in plasma glucose and insulin in response to exercise-training. This group was submitted to a vigorous ergocycle exercise program inducing a surplus in energy expenditure of 1000 kcal/day over habitual energy expenditure during 22 consecutive days. An oral glucose tolerance test (OGTT, 75 g glucose) was performed before and about 16 hours after the experimental period. Fasting plasma glucose as well as its increase over basal level (delta area) during OGTT were not modified by exercise-training (p greater than 0.05), although a marked reduction in insulin was observed, both in the fasting state and during the OGTT (p less than 0.01). To assess the extent to which heredity influenced the response to the treatment, i.e. the genotype-training interaction, within and between MZ twin pairs means of squares were calculated. A significant intrapair resemblance in the response to exercise-training was observed for fasting insulin and delta insulin area/delta glucose area ratio during OGTT, but not for delta insulin area. These results provide some indications about a possible role of the genotype on the sensitivity to reduce plasma insulin in response to exercise-training. However, this hypothesis needs to be substantiated by other experimental data with control over the genotype of subjects.

Quantitating genetic and nongenetic factors that determine plasma sex steroid variation in normal male twins

We have observed that familial factors have a decided influence on the plasma content of sex steroids in men both in the general population and in men of families with prostatic cancer. The contribution of genetic and nongenetic familial factors on the variation of plasma sex steroid content and action has now been investigated in 75 pairs of normal male monozygotic (MZ) twins and 88 pairs of dizygotic (DZ) twins. Zygosity was determined by measuring ten blood proteins and enzymes. The mean plasma values for testosterone (T), dihydrotestosterone (DHT), estradiol (E 2), estrone (E 1), and 3α-androstanediol glucuronide (3α-diol G), free T, LH, FSH, SHBG, age, and degree of adiposity were all similar between the groups of twins. Familial factors ( P < 0.01) accounted for 50% or more of the variation in plasma hormone levels in MZ twins (3α-diol G, 84%; T DHT , 70%; T, 63%; E 1, 63%; free T, 61%; E 2, 57%; DHT, 56%; LH, 55%; and FSH, 54%) except for SHBG, which was 30%. The familial influence was greater in MZ twins than in DZ twins for all measurements except for SHBG. The heritability of the variation of hormone levels in plasma was determined from the equation: 2[r MZ(intraclass correlation) - r DZ]. Genes regulate 25% to 76% of the total variation of plasma content of the hormones except for DHT (12%) and SHBG (<1%). Genetic regulation of tissue DHT formation was suggested by observing a 48% genetic effect on the plasma content of 3α-diol G. These observations suggest that genetic factors make major contributions in regulating estrogen and testosterone levels and tissue DHT production in normal men.

Heredity and changes in hormones and metabolic rates with short-term training.

The purpose of this experiment was to assess the effects of a 22-day training program on resting metabolic rate (RMR), thermic effect of a meal (TEM), and associated hormonal changes. Six pairs of male monozygotic twins were submitted to a 22-day ergocycle exercise program designed to induce a deficit in energy balance of 4.2 MJ per day. RMR and TEM after a 4.2-MJ meal challenge were measured before and after training. Results indicated that RMR and TEM did not change significantly, although a large variation in response between twin pairs was observed. Moreover, training reduced (P less than 0.05) basal and postprandial insulin response, plasma thyroid hormones triiodothyronine (T3), thyroxine (T4), and FT4 (P less than 0.05). Absolute changes in RMR and TEM exhibited significant within-pair resemblance in response, with intraclass correlations reaching r = 0.81 (P less than 0.05) and r = 0.72 (P less than 0.05), respectively. Changes in T4 and FT4 also exhibited moderate within-pair resemblance (0.42 less than or equal to r less than or equal to 0.71). These results suggest that short-term exercise training does not modify RMR and TEM but can significantly decrease plasma levels of insulin and thyroid hormones. Moreover, the similarity of response within twin pairs suggests that heredity plays a role in determining RMR, TEM, and thyroid hormone adaptation to exercise training generating a negative energy balance.

Genotype-controlled changes in body composition and fat morphology following overfeeding in twins

This study investigated the effects of overfeeding on the body composition and fat morphology characteristics of 6 pairs of male monozygotic twins. Each participant was submitted to a 22-day overfeeding period, supplemented by an additional 1000 kcal/day. Significant changes were observed in body composition and fat morphology as shown by increases in body weight, fat mass, sum of 9 skinfolds, and fat cell diameter. Significant within-pair resemblance for absolute changes was observed for body weight, percent body fat, fat mass, sum of skinfolds, trunk skinfolds, and extremity skinfolds, suggesting a role for the genotype in determining the sensitivity of the response to an energy surplus. Significant within-pair resemblance was noted for the biceps, triceps, and thigh with less resemblance noted in the subscapular, abdomen, suprailiac, calf, axillary, and chest sites, suggesting a variation in genotype dependency for subcutaneous fat The results suggest that changes in body fat following short-term overfeeding appear to have a genetic basis.

Genotype dependency of adaptation in adipose tissue metabolism after short-term overfeeding.

The present study investigated the interaction of genotype and short-term overfeeding on adipose tissue metabolism of six pairs of male monozygotic twins. The sedentary nonobese twins were submitted to a 22-day overfeeding period in which their normal daily intake was supplemented by an additional 1,000 kcal/day. A fat tissue biopsy was performed in the suprailiac region before and after overfeeding to determine fat cell diameter and basal and maximal stimulated epinephrine, norepinephrine, and isoproterenol lipolysis from collagenase-isolated fat cells. Fat cell basal and maximal insulin-stimulated glucose conversion into triglycerides (basal and stimulated lipogenesis) were measured using [14C]glucose. Adipose tissue heparin-releasable lipoprotein lipase activity (LPL) was also determined. A repeated measures analysis of variance revealed overfeeding induced significant elevations in basal lipogenesis (P less than 0.05) and fat cell diameter (P less than 0.05). No significant group changes were noted in basal, epinephrine-, norepinephrine-, and isoproterenol-stimulated lipolysis, insulin-stimulated lipogenesis, and LPL activity due to large individual variation in the response to overfeeding. However, significant intrapair resemblance was noted in the changes of the aforementioned variables, suggesting a coherent within-twin pair response, despite large between-pair variation in response. Less within-pair similarity was noted in changes in basal lipogenesis and fat cell diameter. The results of the present study suggest that overfeeding induced a large range of adipose tissue metabolic responses and that the genotype plays a role in determining the sensitivity of adipose tissue adaptation to caloric affluence.