Twin Testosterone Transfer Hypothesis Research Articles

No effects of siblings and twin testosterone transfer on autistic traits.

Having twin and non-twin siblings might influence autistic traits both prenatally and postnatally. The twin testosterone transfer hypothesis suggests that girls with a twin brother are exposed to higher levels of prenatal testosterone than girls with a twin sister, and that increased testosterone exposure masculinizes neural development and increases autistic traits. Postnatally, siblings may provide example behaviour, which could reduce autistic traits. We studied pre- and postnatal influences of twin and non-twin siblings on mother and teacher-reported autistic traits in 7714 dizygotic twins. We examined the effect of sex of the proband child and of the siblings. We fitted regression models (for boys and girls separately) with sex of co-twin and having older and/or younger siblings of each sex as predictors. Girls' mother-reported autistic traits were slightly lower for those with a twin brother than those with a twin sister (β=-.08, p = .001, Cohen's d=-.13). This difference was not replicated in teacher-reported autistic traits (β = .01, p=.734). Boys' (mother and teacher-reported) autistic traits were not related to the sex of their co-twin (ps>0.50). Teacher-reported autistic traits were slightly higher if girls had an older brother (β = .07, p = .013, Cohen's d=.12). Other than this small effect, we found no effect of non-twin siblings on autistic traits in either girls or boys (ps>.18). We did not find increased autistic traits in girls with a twin brother compared to girls with a twin sister. This finding contributes to a body of literature that rejects the twin testosterone transfer hypothesis. In addition, we found little evidence for pre- and postnatal sibling influences. Our findings align with high heritability and absence of shared-environmental influences inASD.

Epigenetic consequences of hormonal interactions between opposite-sex twin fetuses.

Previous studies reported inconsistent evidence about some phenotypic traits of females in human opposite‐sex twins (opposite‐sex females [OSF]) being distinct from females in same‐sex twins (SSF). Comparatively, less evidence showed significant differences between males in OS twins (opposite‐sex males [OSM]) and males in same‐sex twins (SSM). The twin testosterone transfer hypothesis suggests that prenatal exposure of testosterone in utero may be a possible explanation for the differential traits in OSF; however, the underlying mechanism is unknown. Here, we investigated the potential epigenetic effects of hormone interactions and their correlation to the observed phenotypic traits. In the study, DNA methylomic data from 54 newborn twins and histone modification data (H3K4me3, H3K4me1, H3K27me3, and H3K27ac) from 14 newborn twins, including same‐sex females (SSF), OS twins, and same‐sex males (SSM) were generated. We found that OSF were clearly distinguishable from SSF by DNA methylome, while OSM were distinguishable from SSM by H3K4me1 and H3K4me3. To be more specific, compared to SSF, OSF showed a stronger correlation to males (OSM and SSM) in genome‐wide DNA methylation. Further, the DNA methylomic differences between OSF and SSF were linked to the process involving cognitive functions and nervous system regulation. The differential H3K4me3 between OSM and SSM was linked to immune responses. These findings provide epigenetic evidence for the twin testosterone transfer hypothesis and offer novel insights on how prenatal hormone exposure in utero may be linked to the reported differential traits of OS twins.

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

Gender and STEM Subject Choice

Science, Technology, Engineering and Mathematics’ (STEM) knowledge and skills are of increasing importance to the Scottish (and UK) economy in terms of economic growth and better-paid employment opportunities. Shortages of suitably qualified individuals mean that policymakers are concerned to increase the study of STEM subjects at both tertiary and secondary education levels, as the latter feeds the former. Persistent, gendered patterns of STEM subject choice exist at all school qualification levels with, for instance, Biology more likely to be studied by females and Physics by males. These differences have been attributed to social conditioning and gender-biased environments rather than any innate, biological differences with little known about the latter. This paper used Scottish Qualifications Authority (SQA) administrative data for 2002-2009, linked to the Scottish Index of Multiple Deprivation (SIMD), to explore whether biological factors may play a part in STEM subject choice in Scottish state secondary schools. Specifically, it examined the impact that potential exposure to increased levels of testosterone, in-utero, for female twins with male co-twins (the Twin Testosterone Transfer hypothesis) may have on their STEM subject choices. Twins and a control group of closely spaced sibling pairs were identified from SQA administrative data. Logistic regression was employed to examine Maths, Biology, Chemistry, Physics, general Science and Computing subject choices. No evidence of any testosterone effect was found despite clear patterns of gender segregation. The impact of socio-economic background was stark. The odds of individuals from more disadvantaged backgrounds taking named sciences fell as deprivation levels rose. Age-14 educational choices and general age-16 attainment were seen to be critical for studying STEM subjects at Higher, the crucial qualifications for university entry, indicating that policy interventions to increase uptake need to begin well before this to redress social inclusion and gender imbalance issues.

Prenatal testosterone does not explain sex differences in spatial ability

The most consistent sex differences in cognition are found for spatial ability, in which males, on average, outperform females. Utilizing a twin design, two studies have shown that females with male co-twins perform better than females with female co-twins on a mental rotation task. According to the Twin Testosterone Transfer hypothesis (TTT) this advantage is due to in-uterine transmission of testosterone from males to females. The present study tested the TTT across 14 different spatial ability measures, including mental rotation tasks, in a large sample of 19–21-year-old twins. Males performed significantly better than females on all spatial tasks, with effect sizes ranging from η2 = 0.02 to η2 = 0.16. Females with a male co-twin outperformed females with a female co-twin in two of the tasks. The effect sizes for both differences were negligible (η2 < 0.02). Contrary to the previous studies, our results gave no indication that prenatally transferred testosterone, from a male to a female twin, influences sex differences in spatial ability.

Sex differences in non-verbal and verbal abilities in childhood and adolescence

Twin research has shown that females with male co-twins perform better than females with female co-twins on mental rotation. This beneficial effect of having a male sibling on spatial ability could be due to in-uterine transmission of testosterone from males to females (the Twin Testosterone Transfer hypothesis, TTT). The present study explored sex differences and the TTT in non-verbal and verbal abilities in a large sample of twins assessed longitudinally at 2, 3, 4, 7, 9, 10, 12, 14 and 16years of age. Females scored significantly higher than males on both verbal and non-verbal abilities at ages 2, 3 and 4. Males scored significantly higher than females on verbal ability at ages 10 and 12. The effect sizes of all differences were very small. No sex differences in non-verbal or verbal abilities were found at 7, 9, 14 and 16years of age. No support for the TTT was found at any age. The findings indicate that the twin testosterone transfer effect occurs only for specific cognitive abilities, such as mental rotation.

Early-life mortality risks in opposite-sex and same-sex twins: a Danish cohort study of the twin testosterone transfer hypothesis

PurposeTo investigate the twin testosterone transfer (TTT) hypothesis by comparing early-life mortality risks of opposite-sex (OS) and same-sex (SS) twins during the first 15 years of life. MethodsWe performed a population-based cohort study to compare mortality in OS and SS twins. We included 68,629 live-born Danish twins from 1973 to 2009 identified through the Danish Twin Registry and performed piecewise stratified Cox regression and log-binomial regression. ResultsAmong 1933 deaths, we found significantly higher mortality for twin boys than for twin girls. For both sexes, OS twins had lower mortality than SS twins; the difference persisted for the first year of life for boys and for the first week of life for girls. ConclusionsAlthough the mortality risk for OS boys was in the expected direction according to the TTT hypothesis, the results for OS girls pointed in the opposite direction, providing no clear evidence for the TTT hypothesis.