Attention-Deficit/Hyperactivity Disorder (ADHD) is a neurodevelopmental disorder (Wilens, Biederman & Spencer, 2002) and affects approximately 5% of children (Polanczyk, de Lima, Horta, Biederman & Rohde, 2007). About half of those diagnosed in childhood continue to have the diagnosis and symptoms in adulthood (Kessler et al, 2006). The co-occurrence of ADHD with other psychiatric disorder symptoms (Burt et al., 2001; Cole et al., 2009; Polderman et al., 2014) has been suggested to be partly explained by a shared genetic vulnerability (Polderman et al., 2014). However, the strength of the genetic overlap is currently unclear. Also, no study has examined whether the genetic correlations differs between age groups (childhood vs adulthood), by rater (self-report, other informant, combined (parent-teacher, parent-twin, teacher-twin)), or by type of psychiatric disorder symptoms (externalizing, internalizing, neurodevelopmental). To address this gap, we conducted a systematic literature search to identify relevant twin studies, in PubMed, PsycINFO, and EMBASE. A total of 31 articles were identified and included in the present study. The pooled estimates showed that the comorbidity between ADHD and diverse psychiatric disorder symptoms were explained by shared genetic effects rg=0.50 (0.43-0.56). A similar shared genetic overlap between ADHD and psychiatric disorder symptoms was observed in both childhood rg=0.51 (0.42-0.61) and adulthood rg=0.47 (0.40-0.53). Similar results were also found for self-reports rg=0.49 (0.42-0.55), other informants rg=0.50 (0.40-0.60), and combined raters rg=0.51 (0.30-0.69). Further, the strength of the genetic correlations of ADHD with the externalizing rg=0.49 (0.39-0.59), internalizing rg=0.55 (0.40-0.68) and neurodevelopmental rg=0.47 (0.40-0.53) spectrums were similar in magnitude. These findings emphasize the presence of a shared genetic liability between ADHD and externalizing, internalizing and neurodevelopmental disorder symptoms, independent of age and rater.
References
Burt, S. A., Krueger, R. F., McGue, M., Iacono, W. G. (2001). Sources of covariation among attention-deficit/hyperactivity disorder, oppositional defiant disorder, and conduct disorder: The importance of shared environment. Journal of Abnormal Psychology, 4, 516-525.
Cole, J., Ball, H. A., Martin, N. C., Scourfield, J., McGuffin, P. (2009). Genetic overlap between measures of hyperactivity/inattention and mood in children and adolescents. J Am Acad Child Adolesc Psychiatry 48, 1094–1101.
Kessler, R. C., Adler, L., Barkley, R., Biederman, J., Conners, C. K., Demler, O., Faraone, S. V., Greenhill, L. L., Howes, M. J., Secnik, K., Spencer, T., Ustun, T. B., Walters, E. E., Zaslavsky, A. M. (2006). The prevalence and correlates of adult ADHD in the United States: results from the National Comorbidity Survey Replication. Am J Psychiatry, 163, 716-723.
Polanczyk, G., de Lima, M. S., Horta, B. L., Biederman, J., Rohde, L. A. (2007). The worldwide prevalence of ADHD: a systematic review and metaregression analysis. Am J Psychiatry, 164, 942-8.
Polderman, T. J., Hoekstra, R. A., Posthuma, D., Larsson, H. (2014). The co-occurrence of autistic and ADHD dimensions in adults: an etiological study in 17,770 twins. Transl Psychiatry 2014; 4: e435.
Wilens, T. E., Biederman, J., Spencer, T. J. (2002). Attention deficit/hyperactivity disorder across the lifespan. Annual Review Med 53:113–131
Developmental Disorders (e.g. ADHD) , Psychopathology (e.g., Internalizing, Externalizing, Psychosis)
