No Evidence of Genetic Mediation in the Association Between Birthweight and Academic Performance in 2,413 Danish Adolescent Twin Pairs

Petersen, Inge; Jensen, Vibeke Myrup; Bingley, Paul; Christensen, Kaare

doi:10.1375/twin.12.6.564

Cited by 14 publications

(13 citation statements)

References 29 publications

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“…Twins of unknown zygosity have lower socioeconomic status and poorer school performance than the other twin groups (62). If differences between respondents and nonrespondents influence cancer risk, and we exclude the ssUZ twins, the SS twin group is not comparable with the OS twin group in which zygosity information is available for all the twins.…”

Section: Discussionmentioning

confidence: 99%

Risk of Sex-Specific Cancers in Opposite-Sex and Same-Sex Twins in Denmark and Sweden

Ahrenfeldt

Skytthe

Möller

et al. 2015

Cancer Epidemiology, Biomarkers &Amp; Prevention

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Background Increasing evidence shows that some cancers originate in utero. It is hypothesized that elevated exposure to some steroid hormones might increase cancer risk and that hormone transfer between twin fetuses could result in different prenatal exposure to testosterone. Methods This large-scale prospective twin study compared opposite-sex (OS) and same-sex (SS) twins to test the impact of intrauterine exposures on cancer risk. On the basis of the Danish and Swedish twin and cancer registries, we calculated incidence rate ratios for OS and SS twins, whereas standardized incidence ratios (SIR) with 95% confidence intervals (CI) were calculated for OS/SS twins compared with the general population. Results Atotal of 18,001 cancers were identified during 1943–2009. No significant differences were observed between OS and SS twins, neither for the sex-specific cancers nor for cancer at all sites. All-cause cancer was slightly reduced for OS and SS twins compared with the general population, significant for OS males (SIR, 0.95; 95% CI, 0.92–0.98) and for SS males and females (SIR, 0.97; 95% CI, 0.94–0.99). Conclusions Our data suggest that having a male co-twin—which may entail higher exposure to prenatal testosterone—does not increase the risk of sex-specific cancers in OS females. Furthermore, the study supports that twinning per se is not a risk factor of cancer. Impact Findings are reassuring, as they fail to provide evidence for the hypothesis that endocrine or other difference in the in utero milieu affects the risk of sex-specific cancers.

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Section: Discussionmentioning

confidence: 99%

Risk of Sex-Specific Cancers in Opposite-Sex and Same-Sex Twins in Denmark and Sweden

Ahrenfeldt

Skytthe

Möller

et al. 2015

Cancer Epidemiology, Biomarkers &Amp; Prevention

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“…It is a consistent finding in twin studies that those with unknown zygosity have on average poorer health outcome and socioeconomic position than those with known zygosity. 28 The reason is that in order for zygosity assignment to be made, the parents of the twins are required to participate by answering the similarity questions or by providing permission for collection of biological material for DNA testing. If the parents have poorer health or socioeconomic position or 1 or 2 severely sick twins, the likelihood that they participate in zygosity assignment is smaller than average.…”

Section: Discussionmentioning

confidence: 99%

Increased Prevalence of Congenital Heart Defects in Monozygotic and Dizygotic Twins

2013

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Background-Smaller studies and many case series reports indicate that congenital heart defects may be more common in monochorionic twins than in dichorionic twins and singletons. Methods and Results-We investigated congenital heart defect occurrence in all twins and 5% of all singletons born in Denmark in 1977-2001 and followed through 2006 by linking the Danish Twin Registry and Statistics Denmark registers including the National Medical Birth Register and the Danish National Patient Register. Among 41 525 twin individuals, a total of 584 twins (1.4%) had a congenital heart defect registered in the Danish National Patient Register, whereas the corresponding numbers for singletons were 648 of 74 473 (0.87%; P<0.001; ie, a 63% [95% confidence interval, 45-82%] increased risk for congenital heart defect for twins). Patent ductus arteriosus and coarctation of aorta occurred >3 times as often in twins as in singletons, at 3.9 (95% confidence interval, 2.6-5.8) and 3.1 (95% confidence interval, 1.5-6.4), respectively. The increased occurrence in twins was also found in sensitivity analyses including only inpatients or only surgically treated cases regardless of whether preterm patent ductus arteriosus was included. We were not able to demonstrate a higher risk for congenital heart defect among monozygotic twins compared with dizygotic twins, and the congenital heart defect occurrence was also increased in dizygotic twins, who are all dichorionic. Conclusions-Congenital heart defect is more common in twins than in singletons, and the increased occurrence is not restricted to monochorionic twins. Intrauterine surveillance and a postnatal comprehensive cardiac assessment for both twins may be considered regardless of chorionicity and zygosity. (Circulation. 2013;128:1182-1188.)

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“…Teacher ratings in ninth grade supplemented the test scores, also scored on the 0–13 scale. These ratings were subjective evaluations of the students’ overall academic performance during the academic year whereas test scores reflected actual student performance rated by the teachers and/or external examiners at specific times on specific tests (Petersen et al, 2009). The test scores and teacher ratings covered major domains of academic achievement such as mathematics and Danish, which were the main topics included in the present study.…”

Section: Methodsmentioning

confidence: 99%

“…Schools for children with learning disabilities were not required to report test scores and teacher ratings used for statistics to the Ministry of Education. In addition, some private schools such as those following the Waldorf pedagogy as a principle did not test at all (Christensen et al, 2006; Petersen et al, 2009). Test scores were considered missing when an individual had attained some scores but not all.…”

Section: Methodsmentioning

confidence: 99%

“…This was done because of the rather large proportion (approximately 27%) of the sample being twins of unknown zygosity (ssUZ), which made it impossible to allocate all the SS twins to a zygosity group. Supporting the inappropriateness of dropping the ssUZ twins, a study consisting of 2,413 Danish twin pairs from birth cohorts 1986–1990 found that ssUZ twins averaged lower school achievement scores than did twins of known zygosity (Petersen et al, 2009). Because OS twins are always identifiable, these lower-achieving twins would not be dropped from the OS group, as exclusion of the ssUZ twins from the SS group would have biased the results towards better performance for the SS twins.…”

Section: Methodsmentioning

confidence: 99%

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Academic performance of opposite-sex and same-sex twins in adolescence: A Danish national cohort study

Ahrenfeldt

Petersen

Johnson

et al. 2015

Hormones and Behavior

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Testosterone is an important hormone in the sexual differentiation of the brain, contributing to differences in cognitive abilities between males and females. For instance, studies in clinical populations such as females with congenital adrenal hyperplasia (CAH) who are exposed to high levels of androgens in utero support arguments for prenatal testosterone effects on characteristics such as visuospatial cognition and behaviour. The comparison of opposite-sex (OS) and same-sex (SS) twin pairs can be used to help establish the role of prenatal testosterone. However, although some twin studies confirm a masculinizing effect of a male co-twin regarding for instance perception and cognition it remains unclear whether intra-uterine hormone transfer exists in humans. Our aim was to test the potential influences of testosterone on academic performance in OS twins. We compared ninth-grade test scores and teacher ratings of OS (n = 1812) and SS (n = 4054) twins as well as of twins and singletons (n = 13,900) in mathematics, physics/chemistry, Danish, and English. We found that males had significantly higher test scores in mathematics than females (.06–.15 SD), whereas females performed better in Danish (.33–.49 SD), English (.20 SD), and neatness (.45–.64 SD). However, we did not find that OS females performed better in mathematics than SS and singleton females, nor did they perform worse either in Danish or English. Scores for OS and SS males were similar in all topics. In conclusion, this study did not provide evidence for a masculinization of female twins with male co-twins with regard to academic performance in adolescence.

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No Evidence of Genetic Mediation in the Association Between Birthweight and Academic Performance in 2,413 Danish Adolescent Twin Pairs

Cited by 14 publications

References 29 publications

Risk of Sex-Specific Cancers in Opposite-Sex and Same-Sex Twins in Denmark and Sweden

Risk of Sex-Specific Cancers in Opposite-Sex and Same-Sex Twins in Denmark and Sweden

Increased Prevalence of Congenital Heart Defects in Monozygotic and Dizygotic Twins

Academic performance of opposite-sex and same-sex twins in adolescence: A Danish national cohort study

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