The CODATwins Project: The Current Status and Recent Findings of COllaborative Project of Development of Anthropometrical Measures in Twins.

The COllaborative project of Development of Anthropometrical measures in Twins (CODATwins) project is a large international collaborative effort to analyze individual-level phenotype data from twins in multiple cohorts from different environments. The main objective is to study factors that modify genetic and environmental variation of height, body mass index (BMI, kg/m2) and size at birth, and additionally to address other research questions such as long-term consequences of birth size. The project started in 2013 and is open to all twin projects in the world having height and weight measures on twins with information on zygosity. Thus far, 54 twin projects from 24 countries have provided individual-level data. The CODATwins database includes 489,981 twin individuals (228,635 complete twin pairs). Since many twin cohorts have collected longitudinal data, there is a total of 1,049,785 height and weight observations. For many cohorts, we also have information on birth weight and length, own smoking behavior and own or parental education. We found that the heritability estimates of height and BMI systematically changed from infancy to old age. Remarkably, only minor differences in the heritability estimates were found across cultural-geographic regions, measurement time and birth cohort for height and BMI. In addition to genetic epidemiological studies, we looked at associations of height and BMI with education, birth weight and smoking status. Within-family analyses examined differences within same-sex and opposite-sex dizygotic twins in birth size and later development. The CODATwins project demonstrates the feasibility and value of international collaboration to address gene-by-exposure interactions that require large sample sizes and address the effects of different exposures across time, geographical regions and socioeconomic status.

Clostridium difficile in wild rodents and insectivores in the Netherlands.

With wild rodents and insectivores being present around humans and their living, working and food production environments, it is important to gain knowledge of the zoonotic pathogens present in these animals. The enteropathogen Clostridium difficile, an opportunistic anaerobic bacteria, can be carried by both animals and humans, and is distributed globally. It is known that there is genetic overlap between human and animal sources of C. difficile. In this study, the aim was to assess the presence of C. difficile in rodents and insectivores trapped on and around pig and cattle farms in the Netherlands. In total 347 rodents and insectivores (10 different species) were trapped and 39·2% tested positive for presence of C. difficile. For all positive samples the ribotype (RT) was determined, and in total there were 13 different RTs found (in descending order of frequency: 057, 010, 029, 005, 073, 078, 015, 035, 454, 014, 058, 062, 087). Six of the RTs isolated from rodents and insectivores are known to be associated with human C. difficile infection; RT005, RT010, RT014, RT015, RT078 and RT087. The presence of rodents and insectivores in and around food production buildings (e.g. farms) could contribute to the spread of C. difficile in the human environment. In order to enable on-farm management for pathogen control, it is essential to comprehend the role of wild rodents and insectivores that could potentially affect the ecology of disease agents on farms. SIGNIFICANCE AND IMPACT OF THE STUDY: This study shows that rodents and insectivores in and around food production buildings (e.g. farms) can carry Clostridium difficile ribotypes associated with human C. difficile infection (CDI). C. difficile spores in rodent and insectivore droppings are able to survive in the environment for prolonged periods, leading to host-to-host exposure and transmission. Therefore we can state that rodent and insectivore presence on farms is a risk for zoonotic pathogen transmission of C. difficile.

Wild mice in and around the city of Utrecht, the Netherlands, are carriers of Clostridium difficile but not ESBL-producing Enterobacteriaceae, Salmonella spp. or MRSA.

Mice in buildings are a hygiene hazard because they harbour several zoonoses and animal diseases. The aim of this study was to gather information on specific bacteria in house mice caught in the urban environment. Mice caught in snap traps during pest control activities were collected in and around the city of Utrecht, the Netherlands, during May-June 2014, October-November 2015 and September-November 2016. The gut contents were analysed for ESBL/AmpC-producing Enterobacteriaceae, Salmonella spp., and Clostridium difficile and the buccal cavities were swabbed for methicillin-resistant S. aureus (MRSA). In total, 109 house mice (Mus musculus) and 22 wood mice (Apodemus sylvaticus) were examined. One mouse was found positive for Enterobacter spp. Salmonella spp. and MRSA were not found. Of n = 80 mice, 35·0% carried C. difficile (ribotypes in descending order of frequency: 014/020, 258, 002, 005, 013, 056, 081 and two unknown ribotypes). In conclusion, mouse droppings are a hazard for transmission of C. difficile to humans and their environment. SIGNIFICANCE AND IMPACT OF THE STUDY: This study shows that mice in buildings can carry Clostridium difficile ribotypes that are associated with clinical disease in humans. Whether the mice are the source or whether they picked up these bacteria from the human environment has not been investigated. Either way, mouse droppings in the indoor environment are a hazard for transmission of C. difficile to humans.

Changes in genetic risk for emotional eating across the menstrual cycle: a longitudinal study.

BACKGROUND: Previous studies have shown significant within-person changes in binge eating and emotional eating across the menstrual cycle, with substantial increases in both phenotypes during post-ovulation. Increases in both estradiol and progesterone levels appear to account for these changes in phenotypic risk, possibly via increases in genetic effects. However, to date, no study has examined changes in genetic risk for binge phenotypes (or any other phenotype) across the menstrual cycle. The goal of the present study was to examine within-person changes in genetic risk for emotional eating scores across the menstrual cycle. METHOD: Participants were 230 female twin pairs (460 twins) from the Michigan State University Twin Registry who completed daily measures of emotional eating for 45 consecutive days. Menstrual cycle phase was coded based on dates of menstrual bleeding and daily ovarian hormone levels. RESULTS: Findings revealed important shifts in genetic and environmental influences, where estimates of genetic influences were two times higher in post- as compared with pre-ovulation. Surprisingly, pre-ovulation was marked by a predominance of environmental influences, including shared environmental effects which have not been previously detected for binge eating phenotypes in adulthood. CONCLUSIONS: Our study was the first to examine within-person shifts in genetic and environmental influences on a behavioral phenotype across the menstrual cycle. Results highlight a potentially critical role for these shifts in risk for emotional eating across the menstrual cycle and underscore the need for additional, large-scale studies to identify the genetic and environmental factors contributing to menstrual cycle effects.

Neighborhood as a predictor of non-aggressive, but not aggressive, antisocial behaviors in adulthood.

BACKGROUND: Prior meta-analytic work has highlighted important etiological distinctions between aggressive (AGG) and non-aggressive rule-breaking (RB) dimensions of antisocial behavior. Among these is the finding that RB is influenced by the environment more than is AGG. Relatively little research, however, has sought to identify the specific environmental experiences that contribute to this effect. The current study sought to do just this. METHOD: We examined whether unrelated adults residing in the same neighborhood (n = 1915 participants in 501 neighborhoods) were more similar in their AGG and RB than would be expected by chance. Analyses focused on simple multi-level models, with the participant as the lower-level unit and the neighborhood as the upper-level unit. RESULTS: Results revealed little to no evidence of neighborhood-level variance in AGG. By contrast, 11+% of the variance in RB could be predicted from participant neighborhood, results that persisted even when considering the possibility of genetic relatedness across participants and neighborhood selection effects. Moreover, 17% of this neighborhood-level variance in RB was accounted for by neighborhood structural characteristics and social processes. CONCLUSIONS: Findings bolster prior suggestions that broader contextual experiences, like the structural and social characteristics of one's neighborhood, contribute in a meaningful way to RB in particular. Our results also tentatively imply that this association may be environmental in origin. Future work should seek to develop additional, stronger designs capable of more clearly leveraging genetic un-relatedness to improve causal inferences regarding the environment.

The quality of the interparental relationship does not moderate the etiology of child conduct problems.

BACKGROUND: Although there is a clear phenotypic relationship between the quality of the interparental or marital relationship and child conduct problems (CP), the etiology of this association is as yet unclear. One possibility is that this association takes the form of a genotype-environment interaction (G × E), whereby the quality of the interparental relationship acts to moderate the etiology of child CP. The current study sought to evaluate this possibility. METHOD: We examined multiple measures and informant reports of the quality of the interparental relationship in a sample of more than 700 child twin families from the Michigan State University Twin Registry (MSUTR). Analyses consisted of a series of latent G × E models. RESULTS: The 'no moderation' model provided the best fit to the data in nearly all cases, findings that collectively provide strong evidence against the possibility that the etiology of CP is moderated by the quality of the interparental relationship. CONCLUSIONS: Our findings suggest that, contrary to implicit (and sometimes explicit) assumptions in the field, it is not the case that every environmental risk (or protective) factor exacerbates (or suppresses) genetic influences on CP. Future research should seek to delineate the specific environmental experiences that do serve as etiologic moderators of CP, and to clarify how this G × E interplay might change over the course of development.

The effects of circulating testosterone and pubertal maturation on risk for disordered eating symptoms in adolescent males.

BACKGROUND: Testosterone may be a biological factor that protects males against eating disorders. Elevated prenatal testosterone exposure is linked to lower levels of disordered eating symptoms, but effects emerge only after mid-puberty. Whether circulating levels of testosterone account for decreased risk for disordered eating in boys after mid-puberty is currently unknown; however, animal data support this possibility. In rodents, prenatal testosterone's masculinizing effects on sex-differentiated behaviors emerge during puberty when circulating levels of testosterone increase and 'activate' the expression of masculinized phenotypes. This study investigated whether higher levels of circulating testosterone predict lower levels of disordered eating symptoms in adolescent boys, and in particular whether effects are associated with advancing pubertal maturation. METHOD: Participants were 213 male twins from the Michigan State University Twin Registry. The Minnesota Eating Behavior Survey and Eating Disorder Examination Questionnaire assessed several disordered eating symptoms. The Pubertal Development Scale assessed pubertal status. Afternoon saliva samples were assayed for testosterone using enzyme immunoassays. RESULTS: Consistent with animal data, higher levels of circulating testosterone predicted lower levels of disordered eating symptoms in adolescent boys and effects emerged with advancing puberty. Results were not accounted for by several important covariates, including age, adiposity, or mood/anxiety symptoms. CONCLUSIONS: Findings suggest that elevated circulating testosterone may be protective and underlie decreased risk for eating pathology in males during/after puberty, whereas lower levels of testosterone may increase risk and explain why some, albeit relatively few, males develop eating disorders.

Prosocial peer affiliation suppresses genetic influences on non-aggressive antisocial behaviors during childhood.

BACKGROUND: Available research has suggested that affiliation with prosocial peers reduces child and adolescent antisocial behavior. However, the etiologic mechanisms driving this association remain unclear. The current study sought to evaluate whether this association takes the form of a gene-environment interaction (G × E) in which prosocial peer affiliation acts to reduce the consequences of genetic risk for non-aggressive antisocial behavior during childhood. METHOD: Our sample consisted of 500 twin pairs aged 6-10 years from the Michigan State University Twin Registry (MSUTR). RESULTS: The results robustly support moderation by prosocial peer affiliation. Genetic influences on non-aggressive antisocial behavior were observed to be several times larger in those with lower levels of prosocial peer affiliation than in those with higher levels of prosocial peer affiliation. This pattern of results persisted even after controlling for gene-environment correlations and deviant peer affiliation, and when restricting our analyses to those twins who shared all or nearly all of their friends. CONCLUSIONS: Such findings not only suggest that prosocial peer affiliation moderates genetic influences on non-aggressive antisocial behaviors during childhood but also provide support for the theoretical notion that protective environmental experiences may exert their influence by promoting resilience to genetic risk.

Parent-child conflict as an etiological moderator of childhood conduct problems: an example of a 'bioecological' gene-environment interaction.

BACKGROUND: Prior research has suggested that, consistent with the diathesis-stress model of gene-environment interaction (G × E), parent-child conflict activates genetic influences on antisocial/externalizing behaviors during adolescence. It remains unclear, however, whether this model is also important during childhood, or whether the moderation of child conduct problems by negative/conflictive parenting is better characterized as a bioecological interaction, in which environmental influences are enhanced in the presence of environmental risk whereas genetic influences are expressed most strongly in their absence. The current study sought to distinguish between these possibilities, evaluating how the parent-child relationship moderates the etiology of childhood-onset conduct problems. METHOD: We conducted a series of 'latent G by measured E' interaction analyses, in which a measured environmental variable was allowed to moderate both genetic and environmental influences on child conduct problems. Participants included 500 child twin pairs from the Michigan State University Twin Registry (MSUTR). RESULTS: Shared environmental influences on conduct problems were found to be several-fold larger in those with high levels of parent-child conflict as compared with those with low levels. Genetic influences, by contrast, were proportionally more influential at lower levels of conflict than at higher levels. CONCLUSIONS: Our findings suggest that, although the diathesis-stress form of G × E appears to underlie the relationship between parenting and conduct problems during adolescence, this pattern of moderation does not extend to childhood. Instead, results were more consistent with the bioecological form of G × E which postulates that, in some cases, genetic influences may be most fully manifested in the absence of environmental risk.

Advanced paternal age at birth: phenotypic and etiologic associations with eating pathology in offspring.

BACKGROUND: Advanced paternal age at birth has been linked to several psychiatric disorders in offspring (e.g. schizophrenia) and genetic mechanisms are thought to underlie these associations. This study is the first to investigate whether advanced paternal age at birth is associated with eating disorder risk using a twin study design capable of examining both phenotypic and genetic associations. METHOD: In a large, population-based sample of female twins aged 8-17 years in mid-puberty or beyond (n = 1722), we investigated whether advanced paternal age was positively associated with disordered eating symptoms and an eating disorder history [i.e. anorexia nervosa (AN), bulimia nervosa (BN) or binge eating disorder (BED)] in offspring. Biometric twin models examined whether genetic and/or environmental factors underlie paternal age effects for disordered eating symptoms. RESULTS: Advanced paternal age was positively associated with disordered eating symptoms and an eating disorder history, where the highest level of pathology was observed in offspring born to fathers ⩾40 years old. The results were not accounted for by maternal age at birth, body mass index (BMI), socio-economic status (SES), fertility treatment or parental psychiatric history. Twin models indicated decreased genetic, and increased environmental, effects on disordered eating with advanced paternal age. CONCLUSIONS: Advanced paternal age increased risk for the full spectrum of eating pathology, independent of several important covariates. However, contrary to leading hypotheses, environmental rather than genetic factors accounted for paternal age-disordered eating associations. These data highlight the need to explore novel (potentially environmental) mechanisms underlying the effects of advanced paternal age on offspring eating disorder risk.

Do etiological influences on aggression overlap with those on rule breaking? A meta-analysis.

BACKGROUND: Although aggressive (AGG) and non-aggressive rule-breaking (RB) dimensions of antisocial behavior have been shown to be differentially heritable, available studies have disagreed on the extent to which the genetic and environmental factors influencing AGG also influence RB. The current meta-analysis sought to clarify the extent of etiological overlap between AGG and RB. Method Thirteen twin/sibling studies examining the covariation between AGG and RB were collected, of which 11 (with 12 independent samples) were ultimately included in the analyses (n=12923 twin/sibling pairs). Genetic and environmental correlations between AGG and RB served as study effect sizes. When squared, these correlations directly index the proportion of genetic and environmental overlap. Data were analyzed using mixed effect models. RESULTS: Analyses revealed that genetic influences on AGG were largely, but not entirely, distinct from those on RB: only 38.4% of the genetic influences on AGG overlapped with those on RB. Similarly, only 10.2% of the non-shared environmental influences on AGG overlapped with those on RB. Although the conclusion that etiological influences on AGG are partially distinct from those on RB persisted across several potential moderators, the age of the sample and the informant used were found to moderate the extent of overlap. CONCLUSIONS: The findings underscore the presence of meaningful etiological distinctions between AGG and RB, and imply that future conceptualizations of antisocial behavior should be organized (at least in part) around the dimensions of AGG and RB.

Delinquent peer affiliation as an etiological moderator of childhood delinquency.

BACKGROUND: Prior research has indicated that affiliation with delinquent peers activates genetic influences on delinquency during adolescence. However, because other studies have indicated that the socializing effects of delinquent peers vary dramatically across childhood and adolescence, it is unclear whether delinquent peer affiliation (DPA) also moderates genetic influences on delinquency during childhood. Method The current study sought to evaluate whether and how DPA moderated the etiology of delinquency in a sample of 726 child twins from the Michigan State University Twin Registry (MSUTR). RESULTS: The results robustly supported etiological moderation of childhood delinquency by DPA. However, this effect was observed for shared environmental, rather than genetic, influences. Shared environmental influences on delinquency were found to be several-fold larger in those with higher levels of DPA as compared to those with lower levels. This pattern of results persisted even when controlling for the overlap between delinquency and DPA. CONCLUSIONS: Our findings bolster prior work in suggesting that, during childhood, the association between DPA and delinquency is largely (although not solely) attributable to the effects of socialization as compared to selection. They also suggest that the process of etiological moderation is not specific to genetic influences. Latent environmental influences are also amenable to moderation by measured environmental factors.

In vitro inhibition of Eimeria tenella invasion of epithelial cells by phytochemicals.

Resistance to coccidiostats and possible future restrictions on their use raise the need for alternative methods of reducing coccidiosis in poultry. The aim of this study was to evaluate the effect of selected phytochemicals on Eimeria tenella sporozoite invasion in vitro. Four phytochemicals were selected on the basis that they reduce the virulence of Eimeria spp. and/or provide immune modulatory benefits to host cells: betaine, carvacrol, curcumin and Echinacea purpurea extract (EP). Madin-Darby bovine kidney (MDBK) cells were covered by medium containing phytochemicals at the highest concentration which was non-toxic to the cells. Salinomycin 50 µg/ml was positive control; negative control was medium only. E. tenella (Houghton strain) sporozoites were added to wells and after incubation for 2, 4 or 20 h at 37°C, cells were fixed and stained with hematoxylin-eosin. Ten evenly spaced fields per well were photographed and the percentage of cells invaded by sporozoites was calculated and normalized to the control. At 2h, carvacrol, curcumin and EP showed a significantly lower percentage of sporozoite invasion than the untreated control; in contrast, betaine treatment represented a significantly higher invasion percentage. Combining carvacrol with EP inhibited E. tenella invasion more effectively than applying the compounds individually, but the further addition of curcumin did not reduce invasion further. In conclusion, this study shows that invasion of MDBK epithelial cells by E. tenella sporozoites is inhibited in the presence of carvacrol, curcumin, or EP and enhanced by betaine. There may be potential for developing these phytochemicals as anti-coccidial feed or water additives for poultry.

Vermin on pig farms are vectors for Clostridium difficile PCR ribotypes 078 and 045.

Clostridium difficile is a gram positive, spore forming, toxin producing, anaerobic bacteria and an opportunistic pathogen for Man and many animal species, causing diarrhea in young piglets. Piglets probably become colonized from the environment. To investigate the possible spread and transmission of C. difficile by vermin, vermin samples were collected on a pig farm in the Netherlands and investigated for the presence of C. difficile. Samples of house mice (n=53), drain flies (n=39), lesser houseflies (n=95), and yellow mealworms (n=11) were found positive for C. difficile in 66%, 97%, 56% and 100% of cases respectively. C. difficile PCR ribotype 078 was found in all categories of vermin and ribotype 045 was found in two samples from the skeletal muscle of mice. House sparrows found dead on the premises (n=35) and bird droppings (n=26) were also investigated and carried C. difficile in 66% and 4% of cases respectively. PCR ribotype 078 was identified in bird and droppings samples but ribotype 045 was not. We conclude that vermin can play a role in the spread and transmission of C. difficile types 078 and 045 within pig farms and to other locations.

The effects of puberty on genetic risk for disordered eating: evidence for a sex difference.

BACKGROUND: Differences in genetic influences on disordered eating are present across puberty in girls. Heritability is 0% before puberty, but over 50% during and after puberty. Emerging data suggest that these developmental differences may be due to pubertal increases in ovarian hormones. However, a critical piece of evidence is lacking, namely, knowledge of genetic influences on disordered eating across puberty in boys. Boys do not experience increases in ovarian hormones during puberty. Thus, if pubertal increases in genetic effects are present in boys, then factors in addition to ovarian hormones may drive increases in heritability in girls. The current study was the first to examine this possibility in a sample of 1006 male and female twins from the Michigan State University Twin Registry. METHOD: Disordered eating was assessed with the Minnesota Eating Behavior Survey. Pubertal development was assessed with the Pubertal Development Scale. RESULTS: No significant differences in genetic influences on disordered eating were observed in males across any developmental stage. Heritability was 51% in boys during pre-puberty, puberty and young adulthood. By contrast, in girls, genetic factors accounted for 0% of the variance in pre-puberty, but 51% of the variance during puberty and beyond. Sex differences in genetic effects were only significant during pre-puberty, as the best-fitting models constrained heritability to be equal across all males, pubertal females and young adult females. CONCLUSIONS: The results highlight sex-specific effects of puberty on genetic risk for disordered eating and provide indirect evidence of a role for ovarian hormones and/or other female-specific factors.

Genetic and environmental influences on sleep problems: a study of preadolescent and adolescent twins.

BACKGROUND/AIM: The aim of this study was to examine the extent to which additive genetic, shared environmental and non-shared environmental factors contribute to adolescent and preadolescent sleep problems. METHODS: The sample consisted of a cohort of 270 monozygotic and 246 dizygotic twins from a university-based twin registry. RESULTS: Results demonstrated that genetic and environmental influences each appear to be important to adolescent sleep problems. CONCLUSIONS: While the magnitude of genetic influence on sleep problems was consistent with findings from the adult literature, it was smaller than in studies with younger children, suggesting genetic effects may be less influential in adolescence and adulthood.

The death(s) of close friends and family moderate genetic influences on symptoms of major depressive disorder in adolescents.

BACKGROUND: Prior work has suggested that genetic influences on major depressive disorder (MDD) may be activated by the experience of negative life events. However, it is unclear whether these results persist when controlling for the possibility of confounding active gene-environment correlations (rGE). METHOD: We examined a sample of 1230 adopted and biological siblings between the ages of 10 and 20 years from the Sibling Interaction and Behavior Study. MDD was measured via a lifetime DSM-IV symptom count. Number of deaths experienced served as our environmental risk experience. Because this variable is largely independent of the individual's choices/behaviors, we were able to examine gene-environment interactions while circumventing possible rGE confounds. RESULTS: Biometric analyses revealed pronounced linear increases in the magnitude of genetic influences on symptoms of MDD with the number of deaths experienced, such that genetic influences were estimated to be near-zero for those who had experienced no deaths but were quite large in those who had experienced two or more deaths (i.e. accounting for roughly two-thirds of the phenotypic variance). By contrast, shared and non-shared environmental influences on symptoms of MDD were not meaningfully moderated by the number of deaths experienced. CONCLUSIONS: Such results constructively replicate prior findings of genetic moderation of depressive symptoms by negative life events, thereby suggesting that this effect is not a function of active rGE confounds. Our findings are thus consistent with the notion that exposure to specific negative life events may serve to activate genetic risk for depression during adolescence.

Sleep problems and temperament in adolescents.

The aim of this study was to determine the association between temperament and sleep in adolescents. Participants included 516 adolescents and their mothers drawn from the community. Findings indicated that as with younger children, sleep and dimensions of temperament (sociability, impulsivity and negative affect) are related in adolescents.

Preliminary evidence that estradiol moderates genetic influences on disordered eating attitudes and behaviors during puberty.

BACKGROUND: Puberty moderates genetic influences on disordered eating attitudes and behaviors, with little genetic influence before puberty but large (50%) genetic effects during and after puberty. To date, however, nothing is known about the mechanisms that underlie these effects. Estradiol is a particularly promising candidate, as estrogens become elevated at puberty and regulate gene transcription within neurotransmitter systems important for eating-related phenotypes. The aim of this pilot study was to examine whether estradiol levels moderate genetic influences on disordered eating during puberty. METHOD: Participants included 198 female twins (ages 10-15 years) from the Michigan State University Twin Registry. Disordered eating attitudes and behaviors were assessed with the total score, weight preoccupation, body dissatisfaction and binge eating/compensatory behavior subscales of the Minnesota Eating Behavior Survey (MEBS). Afternoon saliva samples were assayed for estradiol levels. Moderation of genetic effects was examined by comparing twin correlations in low versus high estradiol groups. RESULTS: In the low estradiol group, monozygotic (MZ) and dizygotic (DZ) twin correlations for all MEBS scales were similar, suggesting little genetic influence. In the high estradiol group, the MZ twin correlation was more than double the DZ twin correlation, indicating the presence of genetic effects. Findings could not be accounted for by age, body mass index or the physical changes of puberty. CONCLUSIONS: Estradiol may be one important moderator of genetic effects on disordered eating during puberty. Larger twin studies are needed to replicate this pilot work and quantify the extent of genetic moderation.