Abstract
It has been hypothesized that prenatal exposure to testosterone may be associated with traits of attention-deficit/hyperactivity
disorder (ADHD) or autism spectrum disorder (ASD). We conducted a population-based study of dizygotic female twins to elucidate
this hypothesis, assuming that the sex of the co-twin influences the level of prenatal exposure to testosterone. We invited
parents of 24,552 3- to 15-year-old twins to answer questionnaires on traits of ADHD and ASD. We analysed the data using a
proportional odds model with sex of the co-twin as an instrumental variable for prenatal exposure to testosterone of female
twins. We received responses for 6,339 girls from dizygotic twin pairs. Odds ratios for male versus female co-twin were 0.71
(95 % confidence interval 0.61–0.81) for ADHD traits and 0.74 (0.66–0.83) for ASD traits, indicating that a twin brother reduces
traits of ADHD and ASD in females. In conclusion, we found that female twins with a twin brother scored significantly lower
in parent-reported traits of ADHD and ASD than those with a twin sister. The reason for this may be parental reporting bias,
or confounding by unmeasured variables, or a causal effect of an intrauterine environment modified by the sex of the co-twin
in the opposite direction of what we expected.
disorder (ADHD) or autism spectrum disorder (ASD). We conducted a population-based study of dizygotic female twins to elucidate
this hypothesis, assuming that the sex of the co-twin influences the level of prenatal exposure to testosterone. We invited
parents of 24,552 3- to 15-year-old twins to answer questionnaires on traits of ADHD and ASD. We analysed the data using a
proportional odds model with sex of the co-twin as an instrumental variable for prenatal exposure to testosterone of female
twins. We received responses for 6,339 girls from dizygotic twin pairs. Odds ratios for male versus female co-twin were 0.71
(95 % confidence interval 0.61–0.81) for ADHD traits and 0.74 (0.66–0.83) for ASD traits, indicating that a twin brother reduces
traits of ADHD and ASD in females. In conclusion, we found that female twins with a twin brother scored significantly lower
in parent-reported traits of ADHD and ASD than those with a twin sister. The reason for this may be parental reporting bias,
or confounding by unmeasured variables, or a causal effect of an intrauterine environment modified by the sex of the co-twin
in the opposite direction of what we expected.
- Content Type Journal Article
- Category Original Contribution
- Pages 1-7
- DOI 10.1007/s00787-012-0287-4
- Authors
- Jørn Attermann, Department of Epidemiology, School of Public Health, Aarhus University, Bartholins Alle 2, Aarhus C, 8000 Aarhus, Denmark
- Carsten Obel, Department of General Medicine, School of Public Health, Aarhus University, Aarhus, Denmark
- Niels Bilenberg, Child and Adolescent Psychiatric Department, Institute of Public Health, University of Southern Denmark, Odense, Denmark
- Claudia Maria Nordenbæk, Child and Adolescent Psychiatric Department, Institute of Public Health, University of Southern Denmark, Odense, Denmark
- Axel Skytthe, The Danish Twin Register, Institute of Public Health, University of Southern Denmark, Odense, Denmark
- Jørn Olsen, Department of Epidemiology, School of Public Health, Aarhus University, Bartholins Alle 2, Aarhus C, 8000 Aarhus, Denmark
- Journal European Child & Adolescent Psychiatry
- Online ISSN 1435-165X
- Print ISSN 1018-8827