"Evidence suggests that there is substantial comorbidity between attention-deficit/hyperactivity disorder (ADHD) and major depressive disorder in childhood and adolescence. This study aims to investigate the degree to which etiological factors are shared between the symptoms of these significantly heritable disorders," investigators in London, the United Kingdom report (see also Mental Health).

"A twin study design was used to determine to what extent the covariation between the traits of ADHD and depression is genetically or environmentally mediated, based on parental reports. A general community sample of 645 twin pairs aged 5 to 17 years from the Cardiff Study of All Wales and North U.K. Twins project took part in the study. Parent-rated measures of hyperactivity/inattention (Abbreviated Conners Hyperactivity subscale) and depression (Short Mood and Feelings Questionnaire). Phenotypes derived from the scales were significantly correlated in both boys and girls. Bivariate structural equation modeling revealed a large overlap in underlying genetic factors (boys, r(A) = 0.77; girls, r(A) = 0.67) along with a smaller influence of nonshared environment. These findings suggest that there are common genes conferring liability to both hyperactive/inattentive and depressive traits in children and adolescents. This has implications for future molecular genetic research into ADHD and major depressive disorder," wrote J. Cole and colleagues.

The researchers concluded: "Additionally, it indicates that the comorbid clinical presentation of these disorders may reflect a common genetic pathway. J Am. Acad. Child Adolesc. Psychiatry, 2009;48(11):1094-1101."

Cole and colleagues published their study in the Journal of the American Academy of Child and Adolescent Psychiatry (Genetic Overlap Between Measures of Hyperactivity/Inattention and Mood in Children and Adolescents. Journal of the American Academy of Child and Adolescent Psychiatry, 2009;48(11):1094-1101).

For additional information, contact J. Cole, Kings College London, Institute Psychiatry, Social Genetics & Development Psychiatry Center, London SE5 8AF, UK.

The publisher of the Journal of the American Academy of Child and Adolescent Psychiatry can be contacted at: Lippincott Williams & Wilkins, 530 Walnut St., Philadelphia, PA 19106-3621, USA.