Mulligan, A., Anney, R. J. L., O'Regan, M., Chen, W., Butler, L., Fitzgerald, M., Buitelaar, J. K., Steinhausen, H-C., Rothenberger, A., Minderaa, R. B., Nijmeijer, J., Hoekstra, P. J., Oades, R. D., Roeyers, H., Buschgens, C. J. M., Christiansen, H., Franke, B., Gabriels, I., Hartman, C., Kuntsi, J., Marco, R., Meidad, S., Mueller, U., Psychogiou, L., Rommelse, N. N. J., Thompson, M., Uebel, H., Banaschewski, T., Ebstein, R. P., Eisenberg, J., Manor, I., Miranda, A., Mulas, F., Sergeant, J. A., Sonuga-Barke, E. J. S., Asherson, P., Faraone, S. V. and Gill, M.

Autism symptoms in Attention-Deficit/Hyperactivity Disorder: a familial trait which correlates with conduct, oppositional defiant, language and motor disorders.
Journal of Autism and Developmental Disorders, 39, 197-211. DOI 10.1007/s10803-008-0621-3
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Introduction: Symptoms of autism are present in Attention-Deficit/Hyperactivity Disorder (ADHD). We hypothesised that they are familial and index subtypes of ADHD.

Methods: Symptoms of autism were compared in 821 cases of ADHD (DSM-IV), 1050 siblings and 149 healthy children, as a control group. (The main instrument was the Socal Cmmunication Questionnaire, SCQ). Shared familiality of autism symptoms and ADHD was calculated using DeFries-Fulker analysis.

1 - Ratings of autism symptoms were higher in probands than siblings or controls, & higher in male siblings than male controls.

2 - Autism symptoms were familial, and partly shared with familiality of ADHD in males.

3 - Latent class analysis using SCQ-score yielded 5 classes; Class 1 (31%) with few autism symptoms & low comorbidity; Classes 2-4 were intermediate; Class 5 (7%) showed high levels of autism symptoms and comorbidity.

Discussion: Thus autism symptoms in ADHD represent a familial trait that is associated with increased levels of neurodevelopmental and oppositional/conduct disorders.

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