Pairs Of Male Monozygotic Twins Research Articles

Association between salivary flow rate and depressive symptoms with adjustment for genetic and family environmental factors in Japanese twin study.

The association between salivary flow rate (SFR) and depressive symptoms have been inconclusive. The present study aimed to investigate the association between SFR and depressive symptoms with and without adjustment for genetic and family environmental factors. We conducted a cross-sectional study using twins and measured SFR and depressive symptoms as the outcome and explanatory variables, respectively. We also performed three-step regression analyses by first analysing the association between SFR and depressive symptoms without adjustment for genetic and family environmental factors (individual-level analyses). We then performed between-within analyses using monozygotic (MZ) and same-sex dizygotic (DZ) twin pairs, and finally using only MZ twin pairs. These between-within analyses estimated the coefficients adjusted for genetic and family environmental factors. Furthermore, differences in the associations between individual-level and between-within suggest confounding by genetic and family environmental factors. We conducted 448 twins aged ≥20years. In individual-level analyses in males and between-within analyses using MZ and same-sex DZ male twin pairs, SFR associated with depressive symptoms. In between-within analyses using only MZ male twin pairs, SFR did not associate with depressive symptoms. In females, SFR did not associate with depressive symptoms in both individual-level and between-within analyses. The present study revealed that the association between SFR and depressive symptoms was affected by common genetic factors in males. Understanding this association between SFR and depressive symptoms with adjustment for genetic and family environmental factors could lead to an important consideration for the prevention and treatment of hyposalivation.

Leisure-time physical activity and intra-abdominal fat in young adulthood: A monozygotic co-twin control study.

To investigate differences in abdominal fat compartments between young adult monozygotic twin pairs discordant for leisure-time physical activity. Ten young adult male monozygotic twin pairs (age range 32-36 years) discordant for leisure-time physical activity during the past 3 years were systematically selected from a population-based Finnish twin cohort. Magnetic resonance image at the level of the L2-L3 intervertebral disc was used to predict intra-abdominal and subcutaneous abdominal fat masses. Dietary intake was assessed with a 4-day food diary. Inactive twins had 31% more intra-abdominal fat than their active co-twins (mean difference 0.52 kg, 95% CI 0.12 to 0.91, P = 0.016), whereas the difference in subcutaneous abdominal fat was only 13% (P = 0.21) and 3% in body mass index (P = 0.28). Intraperitoneal fat mass was 41% higher among inactive twins compared to their active co-twins (mean difference 0.41 kg, 95% CI 0.11 to 0.70, P = 0.012). Dietary intake did not differ between co-twins. A lower level of physical activity is related to greater accumulation of intra-abdominal fat among healthy adult males in their mid-30s. The findings highlight the importance of leisure-time physical activity independent of genes and diet in the prevention of intra-abdominal fat accumulation from early adulthood onward.

Physical activity, fitness, glucose homeostasis, and brain morphology in twins.

The main aim of the present study (FITFATTWIN) was to investigate how physical activity level is associated with body composition, glucose homeostasis, and brain morphology in young adult male monozygotic twin pairs discordant for physical activity. From a population-based twin cohort, we systematically selected 10 young adult male monozygotic twin pairs (age range, 32-36 yr) discordant for leisure time physical activity during the past 3 yr. On the basis of interviews, we calculated a mean sum index for leisure time and commuting activity during the past 3 yr (3-yr LTMET index expressed as MET-hours per day). We conducted extensive measurements on body composition (including fat percentage measured by dual-energy x-ray absorptiometry), glucose homeostasis including homeostatic model assessment index and insulin sensitivity index (Matsuda index, calculated from glucose and insulin values from an oral glucose tolerance test), and whole brain magnetic resonance imaging for regional volumetric analyses. According to pairwise analysis, the active twins had lower body fat percentage (P = 0.029) and homeostatic model assessment index (P = 0.031) and higher Matsuda index (P = 0.021) compared with their inactive co-twins. Striatal and prefrontal cortex (subgyral and inferior frontal gyrus) brain gray matter volumes were larger in the nondominant hemisphere in active twins compared with those in inactive co-twins, with a statistical threshold of P < 0.001. Among healthy adult male twins in their mid-30s, a greater level of physical activity is associated with improved glucose homeostasis and modulation of striatum and prefrontal cortex gray matter volume, independent of genetic background. The findings may contribute to later reduced risk of type 2 diabetes and mobility limitations.

Discordant Transsexualism in Male Monozygotic Twins: Neuroanatomical and Psychological Differences

One monozygotic male twin pair discordant for transsexualism is described. Both twins were interviewed and tested with the Wechsler Adult Intelligence Scale battery for cognitive functions and they underwent magnetic resonance imaging to measure the volumes of specific cerebral structures. Interviews with the twins and their mother indicated no unusual medical or life history events that could have had a causal role in the emergence of the disorder. Both cognitive function testing and neuroimaging detected differences between the twins that could be related to unexplained epigenetic effects and exogenous hormone usage.

Transsexuality Among Twins: Identity Concordance, Transition, Rearing, and Orientation

ABSTRACT The relative contributions of genetic and environmental factors to the development of gender identity have been debated. Twins were studied that are concordant or discordant for gender identity status in order to provide clarification of this issue. An extensive library search yielded reports of 27 male and 16 female sets concordant or discordant for transsexuality. An Internet bulletin board search and clinical contact requests for participants in a survey of twins in which one or both transitioned located 69 new twin pairs. In addition to asking about matters associated with gender, these new twins were asked about their transition, rearing, and sexual practices. Combining data from the present survey with those from past-published reports, 20% of all male and female monozygotic twin pairs were found concordant for transsexual identity. This was more frequently the case for males (33%) than for females (23%). The responses of our twins relative to their rearing, along with our findings regarding some of their experiences during childhood and adolescence show their identity was much more influenced by their genetics than their rearing.

Plasma levels of interleukin-6 and interleukin-18 after an acute physical exercise: relation with post-exercise energy intake in twins

Increased interleukin-6 (IL-6) plasma levels have been described to occur during physical exercise. A relative reduction in energy intake after physical activity has also been reported after exercise, indicating a possible involvement of IL-6 as an anorexigenic factor. Given the possible effect of interleukins on appetite, we assessed whether a controlled physical activity bout is related with changes in IL-6, IL-6 soluble receptor (IL-6sR), gp130 and interleukin-18 (IL-18) plasma levels, as well as their relation with post-exercise energy intake. A co-twin intervention study was carried out with five young male monozygotic twin pairs. One co-twin performed 45min of submaximal exercise on a treadmill near the anaerobic threshold ending with 7min at 90% VO(2) max, while his co-twin remained non-active. Ad libitum energy intake was tested through a carbohydrate-rich meal test. Venous blood samples were drawn at baseline, immediately after exercise and after the meal ingestion. Plasma concentrations of IL-6, IL-6sR, gp130 and IL-18 were measured via ELISA. IL-6 plasma levels increased after physical activity bout (2.6-fold change; p = 0.04). A less marked trend, although still significant, was observed for plasma levels of IL-6sR and gp130. Plasma levels of IL-18 did not significantly change during exercise. The twins who exercised exhibited significantly lower energy intake (181 versus 1,195kcal; p = 0.04), compared to the co-twins who remained resting. The present study in monozygotic twins shows increased IL-6 plasma levels after acute physical exercise with a significant reduction in energy intake, supporting a linkage between IL-6 and acute post-exercise eating behaviour.

A Population-Based Study of Shared Genetic Variation Between Premorbid IQ and Psychosis Among Male Twin Pairs and Sibling Pairs From Sweden

The strong association between lower IQ and risk for psychosis has led to the suggestion that the search for genes influencing cognition may provide a useful strategy for examining the genetic origins of psychosis. However, research in this area has generally used designs in which twin pairs are selected by case status and with assessment of IQ after the onset of psychosis rather than longitudinal population-based samples. To examine the relationship and shared genetic origin between premorbid IQ and psychotic disorders in a longitudinal population-based cohort. Genetically informative longitudinal study. Population-based cohort in Sweden. Individuals were identified from the population-based Swedish Multi-Generation Register and consisted of male sibling (n = 369 960), monozygotic twin (n = 1986), and dizygotic twin (n = 2253) pairs born between January 1951 and December 1976. Their IQs were measured during compulsory military conscription. Individuals having a subsequent diagnosis of psychosis were identified via the Swedish National Hospital Discharge Register. Heritability estimates for IQ and psychosis were similar to previous estimates, approximately 69% and 56%, respectively. However, the phenotypic correlation between IQ and psychosis was only -0.11, of which 91% was due to shared genetic influences. The proportion of genetic variance for psychosis shared with that for IQ was approximately 7%. Using IQ as a phenotype to identify genes that have an important role in the genetic origin of schizophrenia is unlikely to be a successful strategy. The low correlation seen in this study between premorbid IQ and psychosis vs the higher correlations reported in the literature with postmorbid IQ suggests the correlation between these phenotypes has more to do with the influence that the onset of psychosis has on cognitive functioning than with shared genetic origin.

Pubertal testosterone predicts mental rotation performance of young adult males

Robust sex differences in some spatial abilities that favor males have raised the question of whether testosterone contributes to those differences. There is some evidence for prenatal organizational effects of testosterone on male-favoring spatial abilities, but not much is known about the role of pubertal testosterone levels on adult cognitive abilities. We studied the association between pubertal testosterone (at age 14) and cognitive performance in young adulthood (at age 21-23), assessing male-favoring, female-favoring, and sex-neutral cognitive domains in a population-based sample of 130 male and 178 female twins. Pubertal testosterone was negatively associated with performance in the Mental Rotation Test in young adult men (r=-.27), while among women no significant associations between testosterone and cognitive measures were detected. The significant association among men remained after controlling for pubertal development. Confirmatory within-family comparisons with one-sided significance testing yielded a negative correlation between twin pair differences in testosterone levels and Mental Rotation Test performances in 35 male twin pairs (r=-.32): the twin brother with higher testosterone performed less well on the Mental Rotation Test. That association was evident in 18 pairs of dizygotic male twin pairs (r=-.42; analysis controlling for shared environmental effects). In contrast, the association of differences was not evident among 17 monozygotic male twin pairs (r=-.07; analysis controlling for shared genetic influences). Results suggest that pubertal testosterone levels are related specifically to male-favoring spatial ability and only among men. Within-family analyses implicated possible shared genetic effects between pubertal testosterone and mental rotation ability.

Effect of Body Composition Methodology on Heritability Estimation of Body Fatness.

Heritability estimates of human body fatness vary widely and the contribution of body composition methodology to this variability is unknown. The effect of body composition methodology on estimations of genetic and environmental contributions to body fatness variation was examined in 78 adult male and female monozygotic twin pairs reared apart or together. Body composition was assessed by six methods – body mass index (BMI), dual energy x-ray absorptiometry (DXA), underwater weighing (UWW), total body water (TBW), bioelectric impedance (BIA), and skinfold thickness. Body fatness was expressed as percent body fat, fat mass, and fat mass/height2 to assess the effect of body fatness expression on heritability estimates. Model-fitting multivariate analyses were used to assess the genetic and environmental components of variance. Mean BMI was 24.5 kg/m2 (range of 17.8–43.4 kg/m2). There was a significant effect of body composition methodology (p<0.001) on heritability estimates, with UWW giving the highest estimate (69%) and BIA giving the lowest estimate (47%) for fat mass/height2. Expression of body fatness as percent body fat resulted in significantly higher heritability estimates (on average 10.3% higher) compared to expression as fat mass/height2 (p=0.015). DXA and TBW methods expressing body fatness as fat mass/height2 gave the least biased heritability assessments, based on the small contribution of specific genetic factors to their genetic variance. A model combining DXA and TBW methods resulted in a relatively low FM/ht2 heritability estimate of 60%, and significant contributions of common and unique environmental factors (22% and 18%, respectively). The body fatness heritability estimate of 60% indicates a smaller contribution of genetic variance to total variance than many previous studies using less powerful research designs have indicated. The results also highlight the importance of environmental factors and possibly genotype by environmental interactions in the etiology of weight gain and the obesity epidemic.

Chromosome 22q11.2 microdeletion in monozygotic twins with discordant phenotype and deletion size.

We report on a pair of male monozygotic twins with 22q11.2 microdeletion, discordant phenotype and discordant deletion size. The second twin had findings suggestive of DiGeorge syndrome, while the first twin had milder anomalies without any cardiac malformation. The second twin had presented with intractable convulsion, cyanosis and cardiovascular failure in the fourth week of life and expired on the sixth week of life, whereas the first twin had some characteristic facial appearance with developmental delay but no other signs of the 22q11.2 microdeletion syndrome including cardiovascular malformation. The fluorescence in situ hybridization (FISH) analysis had shown a microdeletion on the chromosome 22q11.2 in both twins. The interphase FISH did not find any evidence for the mosaicism. The genomic DNA microarray analysis, using HumanCytoSNP-12 BeadChip (Illumina), was identical between the twins except different size of deletion of 22q11.2. The zygosity using HumanCytoSNP-12 BeadChip (Illumina) microarray analysis suggested monozygosity. This observation indicates that altered size of the deletion may be the underlying etiology for the discordance in phenotype in monozygotic twins. We think early post zygotic events (mitotic non-allelic homologous recombination) could have been played a role in the alteration of 22q11.2 deletion size and, thus phenotypic variability in the monozygotic twins.

The Role of Attention-Deficit/hyperactivity Disorder in the Association between Verbal Ability and Conduct Disorder

Although there is clear evidence that low verbal ability is a risk factor for conduct disorder (CD), some researchers have questioned whether this association is due to the common comorbidity between attention-deficit/hyperactivity disorder (ADHD) and CD. The present study examined the association among verbal ability, ADHD, and CD in a genetically informative sample in order to examine the role of genes and/or environmental influences shared in common with ADHD on the covariation between verbal ability and CD. Participants were 2744 adolescents from the Center for Antisocial Drug Dependence (CADD), and included 360 monozygotic (MZ) female twin pairs, 221 dizygotic (DZ) female twin pairs, 297 MZ male twin pairs, 220 DZ male twin pairs, and 274 opposite-sex DZ twin pairs. The Diagnostic Interview Schedule for Children (DISC-IV) was used to assess lifetime symptoms of ADHD and CD. Verbal ability was assessed via the Vocabulary subtest of the Wechsler Adult Intelligence Scale III (WAIS-III) for individuals over the age of 16 and the Vocabulary subtest of the Wechsler Intelligence Scale for Children III (WISC-III) for individuals under the age of 16. There was a small but significant negative covariance between verbal ability and CD and between verbal ability and ADHD. Results also suggest that the covariation between verbal ability and CD is due to influences shared in common with ADHD.

The Role of Back Injury or Trauma in Lumbar Disc Degeneration

Exposure discordant twin study. To investigate the effect of injury on lumbar disc degeneration in monozygotic twins with discordant exposures to recalled previous injury/trauma to the lumbar spine. Disc degeneration is considered a primary source of low back pain. Despite this, important determinants of disc degeneration other than genotype have not been identified. One possible important determinant of disc degeneration that has undergone limited investigation is previous back injury. We compared disc degeneration between 37 male monozygotic twin pairs with discordant exposures to recalled previous injury/trauma to the lumbar spine. Data on injury history were obtained through an extensive structured interview. Disc degeneration was assessed using quantitative measures of disc height and disc signal intensity. RESULTS.: Disc degeneration did not differ between twins who reported previous back injury and their uninjured co-twins. This finding was consistent for both disc height and disc signal intensity regardless of whether mean scores or greatest difference at any one lumbar level was used in the analysis. Disc height averaged 0.3 mm higher in the injured twin (P = 0.302), and was on average 0.05% higher at the level of the greatest co-twin difference (P = 0.302). There was no evidence that greater period since injury resulted in greater twin differences in disc degeneration. The current study suggests that back injury based on patient report is not an important predictor of future disc degeneration.

Liver and pancreatic fat content and metabolism in healthy monozygotic twins with discordant physical activity

Ectopic fat in muscle and liver is linked to obesity and type 2 diabetes. Recently, pancreatic lipid accumulation has also been associated with β-cell dysfunction and reduced insulin production, leading to the development of type 2 diabetes. Physical exercise training has been shown to attenuate β-cell dysfunction in patients, but little is known about its effects on pancreatic and hepatic fat accumulation. In this study, we validated in-vivo proton magnetic resonance spectroscopy ((1)H MRS) in pancreatic fat measurement with biochemical measurements in a pig model. Thereafter, the effects of increased physical activity on the amounts of pancreatic and liver fat were studied in eight monozygotic twin pairs who have discordant physical activity and fitness. Pancreatic fat content was studied in 15 pigs using (1)H MRS and/or biochemical analyses. In addition, liver and pancreatic fat were assessed using (1)H MRS in eight monozygotic male twin pairs with 18% mean difference in VO(2max) between the twin brothers. Twins with higher physical fitness had 23% less liver fat (1.3±1.3% vs. 2.1±2.6%, p=0.022) but no such difference was observed in the pancreatic fat (8.2±9.3% vs. 9.8±8.5%, respectively, p=0.3). Hepatic fat content was inversely associated with VO(2max). A positive association was found between pancreatic and liver fat contents (β=5.18, p=0.012). Pancreatic fat content was also associated with insulin sensitivity indexes and plasma adiponectin and glutamyltransferase concentrations. Pancreatic fat content is associated with insulin resistance and hepatic fat content. An active lifestyle seems to beneficially influence hepatic fat metabolism.

The potential role of G2- but not of G0-radiosensitivity for predisposition of prostate cancer

Purpose Comparing the chromosomal radiosensitivity of prostate cancer patients with that of healthy donors. Materials and methods The study was performed on 81 prostate cancer patients characterised by a clinical stage of predominantly pT2c or pT3a and a median age of 67 years. As healthy donors 60 male monozygotic twin pairs were recruited with a median age of 28 years. Chromosomal radiosensitivity was measured using both G0- and G2-assay. Results No difference between healthy donors and prostate cancer patients was detected concerning G0-radiosensitivity, since medians were similar (Hodges–Lehmann estimate: −0.05, 95% CI: −0.18–0.08, p = 0.4167). However, a pronounced difference was determined for G2-radiosensitivity with prostate cancer patients showing a significantly higher sensitivity compared to healthy donors (Hodges–Lehmann estimate: −0.41, 95% CI: −0.53 to −0.30, p = 1.75 −9). Using the 90% quantile of G2-radiosensitivity in healthy donors as a threshold for discrimination the fraction of prostate cancer patients with elevated radiosensitivity increased to 49%. Conclusion G2-, but not G0-radiosensitivity is a promising marker for predisposition of prostate cancer.

Challenging the cumulative injury model: positive effects of greater body mass on disc degeneration

Background context There are differing views as to the causes of disc degeneration. One view, referred to as a cumulative or repetitive injury model, explains disc degeneration, in great part, as the result of “wear and tear” on the disc from routine daily exposures to physical loading or biomechanical forces. Perhaps paradoxically, such physical loading has been thought to be generally beneficial for other structures of the musculoskeletal system. Purpose The goal of this study was to investigate the associations of physical loading from body weight using quantitative measures of disc degeneration. Study design This is an exposure-discordant twin study. Methods We selected 44 pairs of healthy male monozygotic (MZ) twins with 8 kg or more discordance in body weight (mean 13 kg), with lumbar magnetic resonance imaging and bone density measurements available. The main outcome of disc degeneration was assessed through quantitatively measured disc height, and disc signal intensity and signal variation adjusted by the intrabody reference, adjacent cerebrospinal fluid signal, at L1–L4. Data on suspected constitutional and environmental risk factors were available for control of possible confounding factors. Results Higher body weight was associated with 6.2% higher bone density in the lumbar spine, confirming an effective discordance (p<.0001). Disc signal variation was 5.4% higher (“better”) among the heavier MZ co-twins (p=.005), but the 2.6% higher disc heights and 2.9% higher adjusted disc signals were not statistically significant. Conclusions Contrary to common beliefs, our findings suggest that cumulative or repetitive loading because of higher body mass (nearly 30 pounds on average) was not harmful to the discs. In fact, a slight delay in L1–L4 disc desiccation was observed in the heavier men, as compared with their lighter twin brothers.

Outstanding Paper: Medical and Interventional Science Challenging the Cumulative Injury Model: Positive Effects of Greater Body Mass on Disc Degeneration

BACKGROUND CONTEXT: There are differing views as to the causes of disc degeneration. One view, referred to as a cumulative or repetitive injury model, explains disc degeneration, in great part, as the result of ‘‘wear and tear’’ on the disc from routine daily exposures to physical loading or biomechanical forces. Perhaps paradoxically, such physical loading has been thought to be generally beneficial for other structures of the musculoskeletal system. PURPOSE: The goal of this study was to investigate the associations of physical loading from body weight using quantitative measures of disc degeneration. STUDY DESIGN: This is an exposure-discordant twin study. METHODS: We selected 44 pairs of healthy male monozygotic (MZ) twins with 8 kg or more discordance in body weight (mean 13 kg), with lumbar magnetic resonance imaging and bone density measurements available. The main outcome of disc degeneration was assessed through quantitatively measured disc height, and disc signal intensity and signal variation adjusted by the intrabody reference, adjacent cerebrospinal fluid signal, at L1–L4. Data on suspected constitutional and environmental risk factors were available for control of possible confounding factors. RESULTS: Higher body weight was associated with 6.2% higher bone density in the lumbar spine, confirming an effective discordance (p!.0001). Disc signal variation was 5.4% higher (‘‘better’’) among the heavier MZ co-twins (p5.005), but the 2.6% higher disc heights and 2.9% higher adjusted disc signals were not statistically significant. CONCLUSIONS: Contrary to common beliefs, our findings suggest that cumulative or repetitive loading because of higher body mass (nearly 30 pounds on average) was not harmful to the discs. In fact, a slight delay in L1–L4 disc desiccation was observed in the heavier men, as compared with their lighter twin brothers. 2010 Elsevier Inc. All rights reserved.

Challenging The Cumulative Injury Model: Positive Effects Of Greater Body Mass On Disc Degeneration

PURPOSE: There are differing views as to the causes of disc degeneration. One view emphasizes genetic influences, while another, which has been referred to as a cumulative and repetitive injury model, emphasizes physical loading or biomechanical forces. Perhaps paradoxically, physical loading has been thought to be generally beneficial for the structures of the musculoskeletal system, but harmful for the intervertebral disc. The goal of this study was to investigate the associations of routine physical loading from body weight with quantitative measures of disc degeneration. METHODS: We selected 44 pairs of healthy male monozygotic twins with 8 kg or more discordance in body weight (mean 13 kg), with lumbar MRIs and bone density measurements available. The main outcome of disc degeneration was assessed through quantitatively measured disc height, disc signal intensity, and signal irregularity adjusted by the intra-body reference, adjacent cerebrospinal fluid signal. Data on suspected constitutional and environmental risk factors were available for control of possible confounding factors. RESULTS: Our findings suggest that cumulative repetitive loading due to routine physical loading with higher body mass may slightly delay disc desiccation. Whether physical loading has harmful or beneficial effects may depend on the body's capacity to adapt. CONCLUSIONS: Our findings suggest that cumulative repetitive loading due to routine physical loading with higher body mass may slightly delay disc desiccation. Whether physical loading has harmful or beneficial effects may depend on the body's capacity to adapt.

Developmental‐genetic effects on level and change in childhood fears of twins during adolescence

If the adaptive significance of specific fears changes with age, the genetic contribution to individual differences may be lowest at the age of greatest salience. The roles of genes and environment in the developmental-genetic trajectory of five common childhood fears are explored in 1094 like-sex pairs of male and female monozygotic and dizygotic twins assessed on up to three occasions during adolescence (ages 8-18 years). Dichotomous self-ratings of a cluster of five correlated fears from Ollendick's schedule of fears (FSSC-R) were extracted for subjects at each occasion of assessment. The effects of genes and environment on overall level of fears and rates of adolescent decline were explored by fitting an item-response theory ('IRT') model that allowed for individual genetic and environmental differences in initial fear level ('intercept') and rates of adolescent change ('slope') across the repeated waves of measurement. Different forms of the model were explored using Markov Chain Monte Carlo (MCMC) methods to derive the posterior distribution of subject and item parameters from the raw responses. Additive genetic differences affect the common factor underlying the five fear-items. The same genes also affect rates of change with age, especially in boys. Male adolescents with higher overall genetic predisposition to childhood fears tended to show slower recovery with age than subjects with relatively low initial values. Thus, the genetic variance apparently increases with age. This finding is consistent with a prediction that the regulation of genetic differences will be strongest, and thus the additive genetic variance will be smallest, at the age when the particular stimulus is most salient. Items differed in the extent to which they were sensitive to underlying random differences in the rate of developmental change. Individual differences in rates of change with age were more marked in boys than girls.

Configural Cue Performance in Identical Twins Discordant for Posttraumatic Stress Disorder: Theoretical Implications for the Role of Hippocampal Function

A significant subgroup of individuals with posttraumatic stress disorder (PTSD) exhibits chronic, unremitting symptomatology that has also been associated with smaller hippocampal volume. The hippocampus plays a significant role in configural processing of contextual cues that facilitates context-appropriate extinction of conditioned fear. We test the hypothesis that hippocampus-based configural processing deficits are a pre-existing vulnerability factor for unremitting forms of PTSD. Participants included male monozygotic twin pairs who were discordant for combat trauma. In 18 twin pairs the combat-exposed brother developed unremitting PTSD, whereas in 23 pairs the combat-exposed brother never developed PTSD. Participants were compared in the capacity to solve allocentric spatial processing tasks, and this performance was examined for its relationship to the severity of PTSD symptomatology and hippocampal volume. Although not completely differentiated from overall IQ, PTSD combat veterans demonstrated significantly impaired performance in configural processing relative to non-PTSD combat veterans. Despite having neither combat-exposure nor PTSD, the unexposed co-twins of combat veterans with PTSD displayed the same decrements as their brothers. Deficits were significantly related to PTSD severity and hippocampal volume. The current study provides the first evidence that the relevance of the hippocampus in PTSD might be related to pre-existing configural cue processing deficits that predispose individuals to develop unremitting forms of the disorder.

Eating styles, overweight and obesity in young adult twins

To explore the association of eating styles with overweight and obesity in young adults, controlling for identical genetic background in monozygotic twins. Prospective twin cohort study. Finland, 1991-2002. Two-hundred and thirty-three women and 2060 men from the FinnTwin16 study, aged 16 years at baseline (T1), and ranging from 22 to 27 years at the time of the nutritional assessment (T4). Eating styles (Restrictive/overeating, health-conscious, snacking, emotional and externally induced), self-reported at T4, were contrasted with body mass indices (BMIs) at T1 and T4. At T4, obesity (BMI>or=30Kg/m(2)) was significantly cross-sectionally associated with restrictive eating, frequent snacks, eating in the evening, avoiding fatty foods and failure to maintain healthy eating patterns. These associations were independent of BMI at T1. Obese women self-reported more vulnerability to external eating cues and comfort eating than normal-weight women. However, in a multivariable model, only restrictive/overeating and health-conscious eating styles were significant correlates of obesity at T4, independent of gender and BMI at T1. When we controlled for genetic background restricting the analysis to the 39 female and 45 male monozygotic twin pairs discordant for obesity or overweight (BMI>or=25Kg/m(2)), restrictive/overeating eating style was still statistically significantly associated with excess weight. The eating styles of obese young adults differ from their normal-weight counterparts: restrictive eating, overeating and fewer healthy food choices are associated with obesity. Different eating styles may partially explain weight differences in individuals with identical genetic background.