| 1. |
- Lundström, Sebastian, et al.
(författare)
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Trajectories leading to autism spectrum disorders are affected by paternal age: findings from two nationally representative twin studies.
- 2010
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Ingår i: Journal of Child Psychology and Psychiatry, and Allied Disciplines. - : Wiley. - 0021-9630 .- 1469-7610. ; 51:7, s. 850-856
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Tidskriftsartikel (refereegranskat)abstract
- Background: Despite extensive efforts, the causes of autism remain unknown. Advancing paternal age has been associated with various neurodevelopmental disorders. We aim to investigate three unresolved questions: (a) What is the association between paternal age and autism spectrum disorders (ASD)?; (b) Does paternal age moderate the genetic and environmental etiological factors for ASD? (c) Does paternal age affect normal variation in autistic-like traits? Methods: Two nationally representative twin studies from Sweden (n = 11, 122, assessed at age 9 or 12) and the UK (n = 13, 524, assessed at age 9) were used. Categorical and continuous measures of ASD, autistic-like traits and autistic similarity were calculated and compared over paternal age categories. Results: Both cohorts showed a strong association between paternal age and the risk for ASD. A U-shaped risk association could be discerned since the offspring of both the youngest and oldest fathers showed an elevation in the risk for ASD. Autistic similarity increased with advancing paternal age in both monozygotic and dizygotic twins. Both cohorts showed significantly higher autistic-like traits in the offspring of the youngest and oldest fathers. Conclusions: Phenomena associated with paternal age are clearly involved in the trajectories leading to autistic-like traits and ASD. Mechanisms influencing the trajectories might differ between older and younger fathers. Molecular genetic studies are now needed in order to further understand the association between paternal age and ASD, as well as normal variation in social, language, and repetitive behaviors in the general population.
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| 2. |
- Willfors, Charlotte, et al.
(författare)
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On the role of non-shared environment for executive functioning in ADHD : a twin-differences design study
- 2014
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Ingår i: International Journal of Developmental Disabilities. - Stockholm : Karolinska Institutet, Dept of Medical Epidemiology and Biostatistics. - 2047-3877. ; 60:3, s. 163-173
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Tidskriftsartikel (refereegranskat)abstract
- Introduction: The study of differences between monozygotic (MZ) twin pairs with respect to ADHD may provide novel leads to disentangle the environmental contribution driving its phenotypes. Objectives: To examine non-shared environmental influences on executive function in dimensionally defined ADHD. Methods: This study included 27 MZ twin pairs (7 female) aged 11–20 years being moderately to substantially discordant for ADHD traits as assessed by the Attention Problem (AP) scale of the Child Behavior Checklist/Adult Behavior Checklist. The twins completed the Wisconsin Card Sorting Test (WCST) for cognitive flexibility and the Tower Test (TT) for foresighted planning. Two statistical approaches were used to analyze the data. First, correlations between ADHD trait intra-pair differences and WCST and TT scores were calculated. Second, the significance of those intra-pair differences on WCST and TT, using ADHD as categorical variable in clinically discordant pairs, was tested. Results: Both analysing strategies revealed a link between ADHD on one hand, and foresighted planning and inhibitory control on the other hand mediated by non-shared environmental factors. The first statistical approach yielded positive correlations between intra-pairs differences on the AP scale and intra-pair differences on two subscales of the TT: total rule violation (rs = 0·41) and rule-violation-per-item-ratio (rs = 0·38). Findings in categorically discordant pairs were consistent, showing within-pair differences on the same subtests (z-1·63, P = 0·05, one-tailed and z = −1·60, P = 0·05, one-tailed). Conclusions: Findings confirm previous research suggesting ADHD to be a quantitative extreme on a continuum with executive functions being a cognitive marker of ADHD traits. Non-shared environmental factors appear to influence planning skills and inhibitory control.
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