Approximately 1 in 700-1000 boys are born with an extra X chromosome, also known as Klinefelter syndrome (KS). Because of the risk for development of autistic symptoms, it has been suggested that studying individuals with KS may help in the search for cognitive, neural and genetic mechanisms underlying autism symptoms. In order to gain more insight in the gene-brain-behavior relations, it is important to dissect neurocognitive dysfunctions that mediate between the genetic level and the behavioral level.
The present study focuses on theory of mind skills, and underlying cognitive mechanisms, in children with an extra X chromosome.
In total, 60 children (35 boys and 25 girls) with an extra X chromosome, 60 boys and girls with ASD and 110 non-clinical controls participated in the study. The age range was 9 to 18 years. We used the Social Cognitive Skills Test (SCVT) to assess Theory of Mind skills. This test consists of 7 cartoon stories, with 8 questions for each story covering various levels of theory of mind complexity. The study also included a neurocognitive test battery assessing language skills, executive functioning and intellectual functioning.
Theory of mind scores were lower in the group with an extra X chromosome as compared to controls, and scores could not be differentiated from those in children with ASD. In the extra X group, 57 % of the children scored within the atypical range (below the 15th percentile). Performance was similar in boys and girls with an extra X. Regression analysis showed that theory of mind performance was significantly predicted by executive functioning (inhibition, fluency, attention, working memory, mental flexibility), but not by language skills or intellectual functioning.
Our findings suggest that impaired theory of mind might help explain increased vulnerability for autism symptoms in children with an extra X. Executive dysfunctioning seems to play a crucial role in deficiencies in theory of mind. This knowledge may help in diagnosis and treatment of children with an extra X. The absence of gender effects is not only relevant for clinical practice, but may also provide important clues with regard to role of the extra X chromosome in cognitive development and related risk for autism traits.
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