Opposite-sex Pairs Research Articles

Male microchimerism in females: a quantitative study of twin pedigrees to investigate mechanisms.

STUDY QUESTIONDoes having a male co-twin, older brothers, or sons lead to an increased probability of persistent male microchimerism in female members of twin pedigrees?SUMMARY ANSWERThe presence of a male co-twin did not increase risk of male microchimerism and the prevalence of male microchimerism was not explained by having male offspring or by having an older brother.WHAT IS KNOWN ALREADYMicrochimerism describes the presence of cells within an organism that originate from another zygote and is commonly described as resulting from pregnancy in placental mammals. It is associated with diseases with a female predilection including autoimmune diseases and pregnancy-related complications. However, microchimerism also occurs in nulliparous women; signifying gaps in the understanding of risk factors contributing to persistent microchimerism and the origin of the minor cell population.STUDY DESIGN, SIZE, DURATIONThis cross-sectional study composed of 446 adult female participants of the Netherlands Twin Register (NTR).PARTICIPANTS/MATERIALS, SETTING, METHODSParticipants included in the study were female monozygotic (MZ) twins, female dizygotic same-sex twins and females of dizygotic opposite-sex twin pairs, along with the mothers and sisters of these twins. Peripheral blood samples collected from adult female participants underwent DNA extraction and were biobanked prior to the study. To detect the presence of male-origin microchimerism, DNA samples were tested for the relative quantity of male specific Y chromosome gene DYS14 compared to a common β-globin gene using a highly sensitive quantitative PCR assay.MAIN RESULTS AND THE ROLE OF CHANCEWe observed a large number of women (26.9%) having detectable male microchimerism in their peripheral blood samples. The presence of a male co-twin did not increase risk of male microchimerism (odds ratio (OR) = 1.23: SE 0.40, P = 0.61) and the prevalence of male microchimerism was not explained by having male offspring (OR 0.90: SE 0.19, P = 0.63) or by having an older brother (OR = 1.46: SE 0.32, P = 0.09). The resemblance (correlation) for the presence of microchimerism was similar (P = 0.66) in MZ pairs (0.27; SE 0.37) and in first-degree relatives (0.091; SE 0.092). However, age had a positive relationship with the presence of male microchimerism (P = 0.02).LIMITATIONS, REASONS FOR CAUTIONAfter stratifying for variables of interest, some participant groups resulted in a low numbers of subjects. We investigated microchimerism in peripheral blood due to the proposed mechanism of cell acquisition via transplacental blood exchange; however, this does not represent global chimerism in the individual and microchimerism may localize to numerous other tissues.WIDER IMPLICATIONS OF THE FINDINGSImmune regulation during pregnancy is known to mitigate allosensitization and support tolerance to non-inherited antigens found on donor cells. While unable to identify a specific source that promotes microchimerism prevalence within pedigrees, this study points to the underlying complexities of natural microchimerism in the general population. These findings support previous studies which have identified the presence of male microchimerism among women with no history of pregnancy, suggesting alternative sources of microchimerism. The association of detectable male microchimerism with age is suggestive of additional factors including time, molecular characteristics and environment playing a critical role in the prevalence of persistent microchimerism. The present study necessitates investigation into the molecular underpinnings of natural chimerism to provide insight into women’s health, transplant medicine and immunology.STUDY FUNDING/COMPETING INTEREST(S)This work is funded by Royal Netherlands Academy of Science Professor Award (PAH/6635 to D.I.B.); The Netherlands Organisation for Health Research and Development (ZonMw)—Genotype/phenotype database for behavior genetic and genetic epidemiological studies (ZonMw 911-09-032); Biobanking and Biomolecular Research Infrastructure (BBMRI–NL, 184.021.007; 184.033.111); The Netherlands Organisation for Scientific Research (NWO)—Netherlands Twin Registry Repository (NWO-Groot 480-15-001/674); the National Institutes of Health—The Rutgers University Cell and DNA Repository cooperative agreement (NIMH U24 MH068457-06), Grand Opportunity grants Integration of genomics and transcriptomics in normal twins and major depression (NIMH 1RC2 MH089951-01), and Developmental trajectories of psychopathology (NIMH 1RC2 MH089995); and European Research Council—Genetics of Mental Illness (ERC 230374). C.B.L. declares a competing interest as editor-in-chief of Human Reproduction and his department receives unrestricted research grants from Ferring, Merck and Guerbet. All remaining authors have no conflict-of-interest to declare in regards to this work.TRIAL REGISTRATION NUMBERN/A.

COMPARATIVE ANALYSIS OF THE NEONATE BIRTH WEIGHT IN DIFFERENT TYPES OF TIN PREGNANCY

The relevance of the study lies in the significant increase in multiple pregnancies connected with the higher risk of perinatal complications, the controversy over the effects of chorionicity and sex of the babies on their birth weight, the need for timely diagnosis of fetal growth restriction, and associated morbidity.
 The objective of this study was to compare fetal weights at the birth of different variants of twins depending on chorionicity, gestational age, and sex.
 Materials and methods. During 2016-2020, 440 pairs of twins were examined: 375 dichorionic diamniotic and 65 monochorionic diamniotic (38 – boys, 27 – girls). Among dichorionic couples there were 186 (49.6%) opposite-sex, 98 (26.1%) same-sex males and 91 (24.3%) same-sex females. Fetal weight was measured at birth, and its relationship to chorionicity, fetal sex, a combination of same-sex or opposite-sex co-twins, and gestational age was assessed.
 Results. The average weight of 750 fetuses from dichorionic pairs (2570.0 ± 506.43 g) significantly exceeded the weight of 130 fetuses from monochorionic pairs (2333.4 ± 567.24 g, p < 0.0001). The same-sex male (2603.8 ± 532.29 g) and opposite-sex dichorionic diamniotic (2595.6 ± 490.17 g). twins’ masses significantly surpassed the mass of all other twins (p <0.05). In the group of dichorionic twins, the weight of boys exceeded the weight of girls (2638.1 ± 525.96 g vs. 2499.4 ± 475.84 g, p = 0.0002). This pattern was observed both inside the opposite-sex pairs (2674.2 ± 518.17 g vs. 2517.1 ± 448.24 g, p = 0.0019), and same-sex couples of boys compared to same-sex couples of girls (2603.8 ± 532.29 g and 2481.4 ± 503.08 g, respectively, p = 0.0224). No significant difference in the weight of girls of opposite-sex twins compared to same-sex couples was seen. In monochorionic pairs, the weight of male and female fetuses did not differ significantly. Birth weight discordance was found in all types of twins, the highest percentage of discordance was registered in monochorionic boys – 23.7%, second place in frequency took male dichorionic twins – 20.4%. Among the 30 discordant dichorionic opposite-sex twins in 19 (63.3%) cases, the male fetus was heavier. There was no significant difference in fetal weight when women were fertilized naturally and using assisted reproductive technologies. The average weight of children born by surrogate mothers exceeded the weight of children born by non-surrogate mothers (p = 0.0466). In the first pregnancy, children were born with a lower body weight compared to children born as a result of repeated pregnancies and in women who had a history of childbirth.
 Conclusion. The average weight of the fetuses of dichorionic twins was higher than the weight of the neonates f monochorionic pairs. The prevalence of the weight of boys over the weight of girls from dichorionic pairs and the absence of sex difference in fetal weight in monochorionic twins indicates the possibility of different functional activity of the placenta in fetuses of different sexes. Small for gestational age newborns were most often found in the group of female monochorionic twins and opposite-sex dichorionic pairs. Discordance of fetal mass was most common in monochorionic same-sex male twins. In discordant opposite-sex couples, the male fetus more often was heavier. There was no significant difference in newborn weight when women were fertilized naturally and with the use of assisted reproductive technologies. The average weight of surrogate-born children exceeded the weight of children born by non-surrogate mothers. In the first pregnancy, children were born with a lower body weight compared to children of multiparous and multigravida women.

The Differential Heritability of Social Adjustment by Sex.

Sex differences in social adjustment are frequently observed; however, there has been very little research on adaptability in the individual and social domains. The aim of this study was to investigate the sex difference in social abilities, such as high self-appeal, sociability, school adaptation, and home adaptation between school-age males and females. The sample for this study included both same-sex and opposite-sex twin pairs: a total of 467 twin pairs. We classified them into three groups: a group of those in lower classes of elementary school, a group of those in higher classes of elementary school, and a group of those in junior high school. The heritability of school adaptation was estimated to be 95% in males and 54% in females in the junior high school group. The full sex-limitation model showed a better fit in this group, and this means that a qualitative genetic difference exists. For school adaptation, there was no sex difference in lower elementary school classes; however, a quantitative difference appeared in higher classes of elementary school. Moreover, a qualitative difference appeared in junior high school. From this research, it became clear that sex differences in heritability exist for school adaptation, and there was a marked increase from the elementary school children to the junior high school children.

Mechanisms of Inbreeding Avoidance in a Wild Primate

The deleterious effects of inbreeding have been well-documented in both captive and wild populations. Hence, animals are expected to engage in inbreeding avoidance. However, one recent meta-analysis of mate-choice experiments indicates that animals of many species do not avoid mating with kin in experimental settings, and another reports that behavioral inbreeding avoidance is likely to evolve only when kin encounter each other regularly and inbreeding costs are high. These important results call for more detailed data on the patterns and processes of encounter frequency and mating behavior between kin within natural animal populations. Here, we present the first detailed assessment of encounter frequency and behavioral inbreeding avoidance in multiple kin classes in a wild mammal population, the baboons of the Amboseli ecosystem in Kenya. We find that death and dispersal are very effective at separating opposite-sex pairs of close adult kin. Nonetheless, adult kin pairs do sometimes coreside, and we find strong evidence for inbreeding avoidance via mate choice in kin classes with relatedness ≥ 0.25. Notably, maternal kin avoid inbreeding more effectively than paternal kin despite having identical coefficients of relatedness, pointing to the problem of kin discrimination as a potential constraint on effective inbreeding avoidance. Overall, demographic and behavioral processes ensure that inbred offspring are rare in undisturbed social groups (1% of offspring). However, in an anthropogenically disturbed social group with reduced male dispersal, we find inbreeding rates 10x higher. Our study reinforces the importance of demographic and behavioral contexts for understanding the evolution of inbreeding avoidance.

Cord blood androgen levels of females from same sex and opposite sex twins - A pilot study.

Opposite-sex twins have shown behavioural and reproductive differences between females and males. These differences may be determined by higher intrauterine levels of androgens among females that were exposed to a male co-twin. The aim of this study was to compare cord blood androgen levels in females from same-sex and opposite-sex twins. A prospective study. In this pilot study, we compared cord blood androgens (DHEA-S, Δ-4 androstenedione, total testosterone-TT) and sex hormone-binding globulin (SHBG) levels in 20 females from same sex and 20 females from opposite-sex dichorionic diamniotic twins. We used generalized estimating equation (GEE) modelling to assess differences in cord blood androgens between females from same-sex twin pregnancies and females from opposite-sex twin pregnancies. Twenty opposite-sex twin pairs (female-male twins) and 20 same-sex twin pairs (female-female). Cord blood total testosterone, Δ-4 androstenedione, DHEA-S and sex hormone-binding globulin (SHBG) levels. No difference in the levels of androgens as Δ-4 androstenedione, total testosterone and SHBG was identified between females that were exposed to a female co-twin compared with females that were exposed to a male co-twin. DHEA-S levels were significantly lower among females from opposite-sex twins compared with females from same-sex twins. Our preliminary data do not support the hypothesis that femalesexposed to male co-twins are exposed to higher levels of androgens in utero compared with females exposed to female co-twins. Further studies are needed to explain the reported behavioural and reproductive differences among opposite-sex twins.

Erectile Dysfunction in Young Men: Testosterone, Androgenic Polymorphisms, and Comorbidity With Premature Ejaculation Symptoms

BackgroundThe association between erectile dysfunction (ED), free testosterone (T), and androgenic genetic polymorphisms is still unclear. As most studies in the field have focused on older (>40 y.o.) men, data from young men is scarce. In addition, the clinically observed comorbidity between ED and premature ejaculation (PE) has not been explained. AimThe aim of the present study was 3-fold: to assess in a sample of young men (1) the association between ED and T; (2) the role of androgenic genetic polymorphisms in the aforementioned association; and (3) comorbidity between ED and PE symptoms. MethodsStatistical analyses were performed on a population-based sample of 2,302 Finnish men, (Mage = 26.8 years). Hormone samples were available from 317 men, and genotype information was available from a minimum of 1,144 men depending on genetic locus. For twin analyses, the sample contained 533 male individuals from opposite-sex fraternal twin pairs, 491 identical male individuals (110 complete pairs), 493 male individuals from male fraternal twin pairs (92 complete pairs), and 658 siblings of twins. OutcomesThe main outcome measure includes association between levels of salivary T and ED, main effects of the androgen-related genetic polymorphisms on ED scores. Bivariate twin models of PE and ED were fitted to elucidate possible shared etiology. ResultsWe found no significant association between T levels and ED and no significant main effects of the androgenic genetic polymorphisms on ED. We found no evidence suggesting that any of the genetic polymorphisms would moderate the association between T and ED symptoms. We found shared unique environmental influences between PE and ED (rE = .28). Clinical TranslationObtained data suggest that ED has T-independent causes and that any comorbidity between PE and ED is not explained by a set of genes affecting both phenotypes. Strengths & LimitationsFirst, the sample size for both parts of the study was relatively small, which may make some statistical analyses underpowered. Furthermore, as the sample was a population-based sample of relatively young men, the number of clinically relevant ED cases was low. Second, some concerns about T derived from saliva exist because saliva sampling comes with increased risks of error particularly because saliva samples are more vulnerable to contamination. ConclusionWe found no significant association between free T levels, androgenic genetic polymorphisms, and ED in the younger age cohort. Twin analysis suggested a common nonshared environmental component in PE and ED.Zhuravleva1 ZD, Johansson A, Jern P. Erectile Dysfunction in Young Men: Testosterone, Androgenic Polymorphisms, and Comorbidity With Premature Ejaculation Symptoms. J Sex Med 2021;18:265–274.

Corrigendum. Testing the twin testosterone transfer hypothesis-intergenerational analysis of 317 dizygotic twins born in Aberdeen, Scotland.

Study question Does having a male co-twin influence the female twin's reproductive outcomes? Summary answer Women with a male co-twin had the same chances of being pregnant and having children compared to same-sex twin pairs. What is known already According to the twin testosterone transfer (TTT) hypothesis, in an opposite-sex twin pregnancy, testosterone transfer from the male to the female co-twin occurs. A large body of literature supports the negative impact of prenatal testosterone exposure on female's reproductive health in animal models; however, evidence from human studies remains controversial. Study design, size, duration This cohort study included all dizygotic female twins in the Aberdeen Maternity and Neonatal Databank (Scotland) born before 1 January 1979. The 317 eligible women were followed up for 40 years for any pregnancies and the outcome of those pregnancies recorded in the same database. Participants/materials, setting, methods Fertility outcomes (number of pregnancies, number of livebirths and age at first pregnancy) were compared between women with a male co-twin (exposed group, n = 151) and those with a female co-twin (unexposed group, n = 166). Population averaged models were used to estimate odds ratios (OR) and 95% CI for all outcomes with adjusting for potential confounders. Main results and the role of chance There were no differences in chances of having pregnancies (adj. OR 1.33; 95% CI 0.72, 2.45) and livebirths (adj. OR 1.22; 95% CI 0.68, 2.18) between women from same-sex and opposite-sex twin pairs. Women with a male co-twin were more likely to smoke during pregnancy and, in the unadjusted model, were younger at their first pregnancy (OR 2.13; 95% CI 1.21, 3.75). After adjusting for confounding variables (year of birth and smoking status) the latter finding was no longer significant (OR 1.67; 95% CI 0.90, 3.20). Limitations, reasons for caution The dataset was relatively small. For women without a pregnancy recorded in the databank, we assumed that they had not been pregnant. Wider implications of the findings Despite the evidence from animal studies concerning the adverse effects of prenatal testosterone exposure on female health, our results do not support the TTT hypothesis. The finding that women with a male co-twin are more likely to smoke during pregnancy highlights the importance of considering post-socialisation and social effects in twin studies. Study funding/competing interest(s) European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie project PROTECTED (grant agreement No. 722634) and FREIA project (grant agreement No. 825100). No competing interests. Trial registration number N/A.

Testing the twin testosterone transfer hypothesis-intergenerational analysis of 317 dizygotic twins born in Aberdeen, Scotland.

STUDY QUESTIONDoes having a male co-twin influence the female twin’s reproductive outcomes?SUMMARY ANSWERWomen with a male co-twin had the same chances of being pregnant and having children compared to same-sex twin pairs.WHAT IS KNOWN ALREADYAccording to the twin testosterone transfer (TTT) hypothesis, in an opposite-sex twin pregnancy, testosterone transfer from the male to the female co-twin occurs. A large body of literature supports the negative impact of prenatal testosterone exposure on female’s reproductive health in animal models; however, evidence from human studies remains controversial.STUDY DESIGN, SIZE, DURATIONThis cohort study included all dizygotic female twins in the Aberdeen Maternity and Neonatal Databank (Scotland) born before 1 January 1979. The 317 eligible women were followed up for 40 years for any pregnancies and the outcome of those pregnancies recorded in the same database.PARTICIPANTS/MATERIALS, SETTING, METHODSFertility outcomes (number of pregnancies, number of livebirths and age at first pregnancy) were compared between women with a male co-twin (exposed group, n = 151) and those with a female co-twin (unexposed group, n = 166). Population averaged models were used to estimate odds ratios (OR) and 95% CI for all outcomes with adjusting for potential confounders.MAIN RESULTS AND THE ROLE OF CHANCEThere were no differences in chances of having pregnancies (adj. OR 1.33; 95% CI 0.72, 2.45) and livebirths (adj. OR 1.22; 95% CI 0.68, 2.18) between women from same-sex and opposite-sex twin pairs. Women with a male co-twin were more likely to smoke during pregnancy and, in the unadjusted model, were younger at their first pregnancy (OR 2.13; 95% CI 1.21, 3.75). After adjusting for confounding variables (year of birth and smoking status) the latter finding was no longer significant (OR 1.67; 95% CI 0.90, 3.20).LIMITATIONS, REASONS FOR CAUTIONThe dataset was relatively small. For women without a pregnancy recorded in the databank, we assumed that they had not been pregnant.WIDER IMPLICATIONS OF THE FINDINGSDespite the evidence from animal studies concerning the adverse effects of prenatal testosterone exposure on female health, our results do not support the TTT hypothesis. The finding that women with a male co-twin are more likely to smoke during pregnancy highlights the importance of considering post-socialisation and social effects in twin studies.STUDY FUNDING/COMPETING INTEREST(S)European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie project PROTECTED (grant agreement No. 722634) and FREIA project (grant agreement No. 825100). No competing interests.TRIAL REGISTRATION NUMBERN/A

Within-Family Transmission of Alcohol Use Disorder in Parent-Offspring, Sibling, and Cousin Pairs: A Contagion Model.

To determine whether alcohol use disorder (AUD) is transmitted within families as predicted by contagion, we examined parent-offspring, siblings, and cousin pairs ascertained from Swedish registries with a primary case with AUD. Our outcome variable was AUD registration in at-risk secondary cases. In offspring, risks for AUD registration in the 3 years after a parental index registration residing in the same household, neighborhood, or municipality increased by 1.6%, -0.5%, and 0.3%, respectively. For siblings of sibling index cases, parallel results were 3.2%, 1.2%, and 0.3%. For cousins of cousin index cases, no excess risk was seen for those residing in the same neighborhood or municipality. In siblings, AUD transmission was stronger in same versus opposite sex pairs and from older to younger versus younger to older siblings. These results support the hypothesis that AUD is transmitted among close family relationships and over limited geographical distances by a temporally dynamic contagion model.

Neonatal outcomes of extremely preterm twins by sex pairing: an international cohort study

ObjectiveInfant boys have worse outcomes than girls. In twins, the ‘male disadvantage’ has been reported to extend to female co-twins via a ‘masculinising’ effect. We studied the association between sex...

Etiology of Autism Spectrum Disorders and Autistic Traits Over Time

The frequency with which autism spectrum disorders (ASDs) are diagnosed has shown a marked increase in recent years. One suggestion is that this is partly because of secular changes in the environment, yet to our knowledge this hypothesis lacks evidence. To assess whether the relative importance of genetic and environmental associations with ASD and autistic traits has changed over a 16-year and 26-year period. A twin design was used to assess whether the heritability of ASD and autistic traits has changed over time. Data from 2 nationwide Swedish twin cohorts was used: the Swedish Twin Registry (STR; participants born between January 1982 and December 2008) and the Child and Adolescent Twin Study in Sweden (CATSS; participants born between January 1992 and December 2008). Autism spectrum disorder diagnoses were identified for twins in the STR, with follow-up to 2013. Questionnaires assigned screening diagnoses of ASD to CATSS participants and assessed autistic traits. Analyses were performed from September 1, 2018, to March 31, 2019. Each sample was divided into several birth cohorts covering 1982 to 1991 (for the STR only), 1992-1995, 1996-1999, 2000-2003, and 2004-2008. We assessed whether the genetric and environment variance underlying autistic traits changed across birth cohorts and examined whether the relative contribution of genetics and environment to liability for autism changed across birth cohorts. Data were available for 22 678 twin pairs (5922 female same-sex pairs [26.1%], 5563 male same-sex pairs [24.5%], and 11193 opposite-sex pairs [49.4%]) in the STR and 15 280 pairs (4880 female same-sex pairs [31.9%], 5092 male same-sex pairs [33.3%], and 5308 opposite-sex pairs [34.7%]) in CATSS. The heritability of ASD diagnoses in the STR ranged from 0.88 (95% CI, 0.74-0.96) to 0.97 (95% CI, 0.89-0.99). The heritability of screening diagnoses in CATSS varied from 0.75 (95% CI, 0.58-0.87) to 0.93 (95% CI, 0.84-0.98). Autistic traits showed a modest variance increase over time that was associated with increases in genetic and environmental variance, with the total variance increasing from 0.95 (95% CI, 0.92-0.98) to 1.17 (95% CI, 1.13-1.21) over time. Weak evidence was found for changes in the genetic and environmental factors underlying ASD and autistic traits over time. Genetic factors played a consistently larger role than environmental factors. Environmental factors are thus unlikely to explain the increase in the prevalence of ASD.

The association of sex of co-twin and birth size in twins born in Yucatan, Mexico between 2008 and 2017

Background: Birth measures of twins are potentially influenced by sex of co-twin.Aim: To analyse the association between sex of co-twin and birth weight, length and ponderal index in twin infants from Yucatan, Mexico.Subjects and methods: A total of 2057 twin pairs born during 2008–2017 were analysed. Female-female (F-F), male-male (M-M) and male-female (M-F) twin pair types were defined. Multiple linear regression models were used to analyse the association of (1) being female from M-F pairs and birth measures among overall female infants (M-F and F-F), and (2) being male from M-F pairs and birth measures among overall male infants (M-F and M-M). The length of gestation and mothers’ age and level of education were used as covariates.Results: Models showed that being male from M-F pairs was associated with increases of 81 g in birth weight and 0.61 cm in length, compared to males from M-M pairs, and being female from opposite-sex pairs was associated with increases of 0.36 cm in length, compared to females from same-sex pairs.Conclusions: Males from M-F pairs show greater birth size than males from same-sex pairs, which supports the hypothesis that birth measures of twins are influenced by sex of the co-twin.

Harmonizing behavioral outcomes across studies, raters, and countries: application to the genetic analysis of aggression in the ACTION Consortium.

Aggression in children has genetic and environmental causes. Studies of aggression can pool existing datasets to include more complex models of social effects. Such analyses require large datasets with harmonized outcome measures. Here, we made use of a reference panel for phenotype data to harmonize multiple aggression measures in school-aged children to jointly analyze data from five large twin cohorts. Individual level aggression data on 86,559 children (42,468 twin pairs) were available in five European twin cohorts measured by different instruments. A phenotypic reference panel was collected which enabled a model-based phenotype harmonization approach. A bi-factor integration model in the integrative data analysis framework was developed to model aggression across studies while adjusting for rater, age, and sex. Finally, harmonized aggression scores were analyzed to estimate contributions of genes, environment, and social interaction to aggression. The large sample size allowed adequate power to test for sibling interaction effects, with unique dynamics permitted for opposite-sex twins. The best-fitting model found a high level of overall heritability of aggression (~60%). Different heritability rates of aggression across sex were marginally significant, with heritability estimates in boys of ~64% and ~58% in girls. Sibling interaction effects were only significant in the opposite-sex twin pairs: theinteraction effect of males on their female co-twin differed from the effect of females on their male co-twin. An aggressive female had a positive effect on male co-twin aggression, whereas more aggression in males had a negative influence on a female co-twin. Opposite-sex twins displayed unique social dynamics of aggressive behaviors in a joint analysis of a large, multinational dataset. The integrative data analysis framework, applied in combination with a reference panel, has the potential to elucidate broad, generalizable results in the investigation of common psychological traits in children.

Dementia risk in women higher in same-sex than opposite-sex twins.

Hormones may be one possible mechanism underlying sex differences in dementia incidence. We examined whether presumed differential prenatal hormone milieu is related to dementia risk by comparing dementia rates in same- and opposite-sex dizygotic twin pairs in male and female twins. The sample comprised 43,254 individuals from dizygotic twin pairs aged 60 and older from the Swedish Twin Registry. Survival analyses were conducted separately for females and males. Female twins from opposite-sex pairs had significantly lower dementia risk than female twins from same-sex pairs, but the differences emerged only after age 70 (hazard ratio = 0.64, P = 0.004). Results were not explained by postnatal risk factors for dementia, and no interaction between twin type and apolipoprotein E (APOE) ε4 was found. Male twins from same-sex versus opposite-sex pairs did not differ significantly. The results suggest that relatively masculine prenatal hormone milieus correlate with lower dementia risk in females.

Geographical proximity and the transmission of drug abuse among siblings: evaluating a contagion model in a Swedish National Sample.

Can drug abuse (DA) be transmitted psychologically between adult siblings consistent with a social contagion model? We followed Swedish sibling pairs born in 1932-1990 until one of them, sibling1 (S1), had a first DA registration. We then examined, using Cox regression, the hazard rate for a first registration for DA in sibling2 (S2) within 3 years of a first DA registration in S1 as a function of their geographical proximity. We examined 153 294 informative pairs. To control for familial confounding, we repeated these analyses in sibships containing multiple pairs, comparing risk in different siblings with their proximity to S1. DA was recorded in medical, criminal or pharmacy registries. The best-fit model predicted risk for DA in S2 as a function of the log of kilometres between S1 and S2 with parameter estimates (±95% confidence intervals) of 0.94 (0.92; 0.95). Prediction of DA included effects of cohabitation and an interaction of proximity and time since S1 registration with stronger effects of proximity early in the follow-up period. Proximity effects were stronger for smaller S1-S2 age differences and for same- v. opposite-sex pairs. Sibship analyses confirmed sibling-pair results. Consistent with a social contagion model, the probability of transmission of a first registration for DA in sibling pairs is related to their geographical proximity and similarity in age and sex. Such effects for DA are time-dependent and include cohabitation effects. These results illustrate the complexity of the familial aggregation of DA and support efforts to reduce their contagious spread within families in adulthood.

The Chinese National Twin Registry: a ‘gold mine’ for scientific research

The Chinese National Twin Registry (CNTR) currently includes data from 61566 twin pair from 11 provinces or cities in China. Of these, 31705, 15060 and 13531 pairs are monozygotic, same-sex dizygotic and opposite-sex dizygotic pairs, respectively, determined by opposite sex or intrapair similarity. Since its establishment in 2001, the CNTR has provided an important resource for analysing genetic and environmental influences on chronic diseases especially cardiovascular diseases. Recently, the CNTR has focused on collecting biologic specimens from disease-concordant or disease-discordant twin pairs or from twin pairs reared apart. More than 8000 pairs of these twins have been registered, and blood samples have been collected from more than 1500 pairs. In this review, we summarize the main findings from univariate and multivariate genetic effects analyses, gene-environment interaction studies, omics studies exploring DNA methylation and metabolomic markers associated with phenotypes. There remains further scope for CNTR research and data mining. The plan for future development of the CNTR is described. The CNTR welcomes worldwide collaboration.

Sex-biased dispersal and inbreeding avoidance in Hokkaido brown bears

AbstractNatal dispersal likely plays an important role in avoiding inbreeding among large carnivores. We tested the hypothesis that male-biased dispersal reduces close inbreeding by limiting the spatial overlap of opposite-sex pairs of close relatives in brown bears (Ursus arctos) in the Shiretoko Peninsula, Hokkaido, Japan. We genotyped 837 individuals collected in 1998–2017 at 21 microsatellite loci and performed parentage analysis. To calculate natal dispersal distance, we considered the site where the mother was identified as the birthplace of her offspring, and the site where the offspring were identified as their dispersed place. As predicted, we found that dispersal distances were significantly greater for males (12.4 km ± 1.0) than for females (7.7 km ± 0.9), and those for males increased from 3 years old, indicating that males begin to disperse around the time sexual maturation begins. Relatedness decreased with distance among pairs of females, and the mean relatedness was significantly higher between pairs of females than between pairs of males or between female–male pairs within 3 km. Closely related female–male pairs rarely (5–6%) resided in close proximity (< 3 km), compared with pairs of closely related females. Our study revealed that the potential for close inbreeding was low in Hokkaido brown bears because males are effective dispersers.

Sex-specific differences in the intracellular proteome of human endothelial cells from dizygotic twins

Differences between men and women are being continuously identified in many human diseases. The underlying reasons are not yet fully understood. Beside the influence of endogenous hormones and life style, intrinsic sex-specific dimorphisms at the cellular level may also play a role. HUVECs from twin pairs of opposite sex provide an excellent tool to address the question of sex-specific differences at the molecular level. We compared for the first time protein levels of male and female HUVECs from dizygotic twins using a proteomic approach. To investigate differences under basal and stress conditions, cells were either left untreated or wounded and serum starved for different time points. Approximately 10% of all proteins monitored showed significant sexual dimorphisms in their level under the different conditions tested. The majority of the proteins displayed a higher abundance in female cells. The magnitude of the difference in protein levels between male and female cells was rather small. The most prominent differences throughout all conditions were observed for several X-chromosome encoded proteins with higher levels in female (UBA1, HDHD1) or in male cells (G6PD). Proteins involved in basic cellular processes, such as gene expression and translation (e.g. HMGN1, SRP54) displayed sex-specific levels in particular conditions only. SignificanceThis study provides novel insights into sexual dimorphic protein levels in HUVECs from twin pairs of the opposite sex. The findings identify proteins with sex-specific differences in their levels under different cell culture conditions. The study also highlights the presence of X-chromosome encoded proteins escaping X-chromosomal inactivation. The results emphasize the need to consider the cellular sex of male and female HUVECs in in vitro experiments.

Nonverbal cognition across genetic and environmentally informative kinships: The case for opposite-sex twin pairs and virtual twins

The extent to which prenatal intrauterine testosterone affects cognitive development in females has been of interest. Previous twin research has, however, been limited in its attempts to disentangle prenatal and psychosocial environmental factors influencing cognitive development. The current study applied a novel approach to addressing this concern. Specifically, the nonverbal cognitive performances of female opposite-sex dizygotic co-twins (DZOSfs) and female opposite-sex virtual co-twins (same-age unrelated siblings or VTOSfs) were compared to separate the biological and environmental influences on the nonverbal IQ score and its component subtests. The DZOSf twins showed a trend toward outperforming the younger VTOSf twins on the Block Design subtest only. Using these biologically and environmentally informative kinships offers a novel approach to understanding sex differences in nonverbal cognition. Including VTOSfs as a comparison group creates an experimental design that eliminates confounds and spurious associations left unaddressed in prior twin research.

See how they run: increased ranging behavior counters potential Allee effects in experimentally introduced house mice on an island

Whether the behaviors of individuals at low population densities differ from those at higher densities is critically informative for predictions of theoretical and experimental ecology, as well as for the conservation management of endangered or introduced species. The globally widespread house mouse Mus musculus is a frequently invasive species; detailed analyses of its low-density behavior will allow for better understanding of population dynamics at early stages of invasions and for generating clearer designs of timely management interventions. Opposite-sex pairs of house mice were released in a small number of replicates at opposite ends of a small, 6 ha island in New Zealand, that had been made experimentally rodent-free, to investigate spatial distributions and ranging behaviors at very low densities by simulating a new invasion of the island with each release trial. Successfully introduced mice (n = 15) of both sexes had twofold greater nightly movements, and tenfold larger range sizes, relative to mice trapped and tracked on the same island prior to eradication. This allowed new arrivals to rapidly and reliably overlap with the range of the opposite sex on the island, especially during the breeding season, suggesting that the driver behind increased ranging was mate searching. Despite the study’s small total sample size, the dramatically increased ranging behaviors exhibited by new arrivals on a mouse-free island imply that this species may avoid potential Allee effects through success in mate searching even at low density. Such behavioral shifts in ranging could contribute to the pervasive success of house mice in founding invasive populations even at extremely low initial densities.