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Aetiology for the covariation between combined type ADHD and reading difficulties in a family study: the role of IQ

Authors

  • Celeste H.M. Cheung,

    1. King’s College London, MRC Social, Genetic and Developmental Psychiatry Centre, Institute of Psychiatry, London, UK
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  • Alexis C. Wood,

    1. Department of Epidemiology and Section of Statistical Genetics, University of Alabama at Birmingham, Birmingham, AL, USA
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  • Yannis Paloyelis,

    1. Department of Neuroimaging and Department of Psychology, Institute of Psychiatry, King’s College London, London, UK
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  • Alejandro Arias-Vasquez,

    1. Department of Human Genetics, Radboud University Nijmegen Medical Center, Nijmegen
    2. Department of Psychiatry, Donders Institute for Brain, Cognition and Behavior, Centre for Neuroscience, Radboud University Nijmegen Medical Center, Nijmegen
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  • Jan K. Buitelaar,

    1. Department of Cognitive Neuroscience, Donders Institute for Brain, Cognition and Behavior, Centre for Neuroscience, Radboud University Nijmegen Medical Center, Nijmegen, The Netherlands
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  • Barbara Franke,

    1. Department of Human Genetics, Radboud University Nijmegen Medical Center, Nijmegen
    2. Department of Psychiatry, Donders Institute for Brain, Cognition and Behavior, Centre for Neuroscience, Radboud University Nijmegen Medical Center, Nijmegen
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  • Ana Miranda,

    1. Department of Developmental and Educational Psychology, University of Valencia, Valencia
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  • Fernando Mulas,

    1. Department of Neuropaediatrics, La Fe University Hospital, Faculty of Medicine, Valencia, Spain
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  • Nanda Rommelse,

    1. Department of Psychiatry, Donders Institute for Brain, Cognition and Behavior, Centre for Neuroscience, Radboud University Nijmegen Medical Center, Nijmegen
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  • Joseph A. Sergeant,

    1. Department of Clinical Neuropsychology, Vrije Universiteit, Amsterdam, The Netherlands
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  • Edmund J. Sonuga-Barke,

    1. Developmental Brain-Behaviour Laboratory, University of Southampton, Southampton, UK
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  • Stephen V. Faraone,

    1. Department of Experimental Clinical and Health Psychology, Ghent University, Ghent, Belgium
    2. Department of Neuroscience, SUNY Upstate Medical University, Syracuse, NY
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  • Philip Asherson,

    1. King’s College London, MRC Social, Genetic and Developmental Psychiatry Centre, Institute of Psychiatry, London, UK
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  • Jonna Kuntsi

    1. King’s College London, MRC Social, Genetic and Developmental Psychiatry Centre, Institute of Psychiatry, London, UK
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Abstract

Background:  Twin studies using both clinical and population-based samples suggest that the frequent co-occurrence of attention deficit hyperactivity disorder (ADHD) and reading ability/disability (RD) is largely driven by shared genetic influences. While both disorders are associated with lower IQ, recent twin data suggest that the shared genetic variability between reading difficulties and ADHD inattention symptoms is largely independent from genetic influences contributing to general cognitive ability. The current study aimed to extend the previous findings that were based on rating scale measures in a population sample by examining the generalisability of the findings to a clinical population, and by measuring reading difficulties both with a rating scale and with an objective task. This study investigated the familial relationships between ADHD, reading difficulties and IQ in a sample of individuals diagnosed with ADHD combined type, their siblings and control sibling pairs.

Methods:  Multivariate familial models were run on data from 1,789 individuals at ages 6–19. Reading difficulties were measured with both rating scale and an objective task. IQ was obtained using the Wechsler Intelligence Scales (WISC–III/WAIS–III).

Results:  Significant phenotypic (.2–.4) and familial (.3–.5) correlations were observed among ADHD, reading difficulties and IQ. Yet, 53%–72% of the overlapping familial influences between ADHD and reading difficulties were not shared with IQ.

Conclusions:  Our finding that familial influences shared with general cognitive ability, although present, do not account for the majority of the overlapping familial influences on ADHD and reading difficulties extends previous findings from a population-based study to a clinically ascertained sample with combined type ADHD.

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