Stephen V Faraone1, Laura Ghirardi2, Ralf Kuja-Halkola2, Paul Lichtenstein2, Henrik Larsson3. 1. State University of New York Upstate Medical University, Syracuse, and K.G. Jebsen Centre for Research on Neuropsychiatric Disorders, University of Bergen, Bergen, Norway. Electronic address: sfaraone@childpsychresearch.org. 2. Karolinska Institutet, Stockholm. 3. School of Medical Sciences, Örebro University, Örebro, Sweden.
Abstract
OBJECTIVE: Although many studies document an association between attention-deficit/hyperactivity disorder (ADHD) and intellectual disability (ID), little is known about the etiology of this comorbidity and how it should be addressed in clinical settings. We sought to clarify this issue. METHOD: All individuals born in Sweden between 1987 and 2006 (n = 2,049,587) were identified using the Medical Birth Register (MBR). From this we selected 7 cohorts of relatives: 1,899,654 parent-offspring pairs, 4,180 monozygotic twin pairs, 12,655 dizygotic twin pairs, 914,848 full sibling pairs, 136,962 maternal half-sibling pairs, 134,502 paternal half-sibling pairs, and 2,790,164 full cousin pairs. We used within-individual and within-family analyses to assess the association between ADHD and ID. RESULTS: Individuals with ID were at increased risk for ADHD compared to those without ID, and relatives of participants with ID were at increased risk of ADHD compared with relatives of those without ID. The magnitude of this association was positively associated with the fraction of the genome shared by the relative pair and was lower for severe compared with mild and moderate ID. Model-fitting analyses demonstrated that 91% of the correlation between the liabilities of ADHD and ID was attributable to genetic factors. CONCLUSION: These data provide evidence that nearly all of the comorbidity between ADHD and ID can be attributed to genetic factors, which has implications for diagnostic practice.
OBJECTIVE: Although many studies document an association between attention-deficit/hyperactivity disorder (ADHD) and intellectual disability (ID), little is known about the etiology of this comorbidity and how it should be addressed in clinical settings. We sought to clarify this issue. METHOD: All individuals born in Sweden between 1987 and 2006 (n = 2,049,587) were identified using the Medical Birth Register (MBR). From this we selected 7 cohorts of relatives: 1,899,654 parent-offspring pairs, 4,180 monozygotic twin pairs, 12,655 dizygotic twin pairs, 914,848 full sibling pairs, 136,962 maternal half-sibling pairs, 134,502 paternal half-sibling pairs, and 2,790,164 full cousin pairs. We used within-individual and within-family analyses to assess the association between ADHD and ID. RESULTS: Individuals with ID were at increased risk for ADHD compared to those without ID, and relatives of participants with ID were at increased risk of ADHD compared with relatives of those without ID. The magnitude of this association was positively associated with the fraction of the genome shared by the relative pair and was lower for severe compared with mild and moderate ID. Model-fitting analyses demonstrated that 91% of the correlation between the liabilities of ADHD and ID was attributable to genetic factors. CONCLUSION: These data provide evidence that nearly all of the comorbidity between ADHD and ID can be attributed to genetic factors, which has implications for diagnostic practice.
Authors: Isabell Brikell; Laura Ghirardi; Brian M D'Onofrio; David W Dunn; Catarina Almqvist; Søren Dalsgaard; Ralf Kuja-Halkola; Henrik Larsson Journal: Biol Psychiatry Date: 2017-08-12 Impact factor: 13.382
Authors: Jessica A Kaczorowski; Taylor F Smith; Amanda M Shrewsbury; Leah R Thomas; Valerie S Knopik; Maria T Acosta Journal: Behav Genet Date: 2020-02-05 Impact factor: 2.805
Authors: Jessica Klusek; Shannon L O'Connor; Alexandra Hickey; Kimberly J Hills; Leonard Abbeduto; Jane E Roberts Journal: Am J Intellect Dev Disabil Date: 2022-05-01
Authors: Laura Ghirardi; Qi Chen; Zheng Chang; Ralf Kuja-Halkola; Charlotte Skoglund; Patrick D Quinn; Brian M D'Onofrio; Henrik Larsson Journal: J Child Psychol Psychiatry Date: 2019-10-18 Impact factor: 8.982