Consortium neuroscience of attention deficit/hyperactivity disorder and autism spectrum disorder: the ENIGMA adventure

Neuroimaging has been extensively used to study brain structure and function in individuals with attention deficit/hyperactivity disorder (ADHD) and autism spectrum disorder (ASD) over the past decades. Two of the main shortcomings of the neuroimaging literature of these disorders are the small sample sizes employed and the heterogeneity of methods used. In 2013 and 2014, the ENIGMA-ADHD and ENIGMA-ASD working groups were respectively, founded with a common goal to address these limitations. Here, we provide a narrative review of the thus far completed and still ongoing projects of these working groups. Due to an implicitly hierarchical psychiatric diagnostic classification system, the fields of ADHD and ASD have developed largely in isolation, despite the considerable overlap in the occurrence of the disorders. The collaboration between the ENIGMA-ADHD and -ASD working groups seeks to bring the neuroimaging efforts of the two disorders closer together. The outcomes of case-control studies of subcortical and cortical structures showed that subcortical volumes are similarly affected in ASD and ADHD, albeit with small effect sizes. Cortical analyses identified unique differences in each disorder, but also considerable overlap between the two, specifically in cortical thickness. Ongoing work is examining alternative research questions, such as brain laterality, prediction of case-control status, and anatomical heterogeneity. In brief, great strides have been made toward fulfilling the aims of the ENIGMA collaborations, while new ideas and follow-up analyses continue that include more imaging modalities (diffusion MRI and resting-state functional MRI), collaborations with other large databases, and samples with dual diagnoses.Martine Hoogman is supported by a personal Veni grant of the Netherlands Organization for Scientific Research (NWO, grant number 91619115). Odile A. van den Heuvel is supported by a personal VIDI grant of the Netherlands Organization for Scientific Research (NWO/ZonMw, number 91717306). This work has further benefited from grants for the NeuroIMAGE study which was supported by NIH Grant R01MH62873 (to Stephen V. Faraone), NWO Large Investment Grant 1750102007010 (to Jan Buitelaar), ZonMW grant 60‐60600‐97‐193, NWO grants 056‐13‐015 and 433‐09‐242, and matching grants from Radboud University Nijmegen Medical Center, University Medical Center Groningen and Accare, and Vrije Universiteit Amsterdam. This also included support from the European Community's Seventh Framework Programme (FP7/2007‐2013) under grant agreement number 278948 (TACTICS), 602805 (Aggressotype), 603016 (MATRICS), and 602450 (Imagemend), and the Innovation Medicine Initiative grants 115300 (EU‐AIMS) and 777394 (AIMS‐2‐TRIALS). Support was also received from the Dutch National Science Agenda for the NWA NeurolabNL project (grant 400 17 602). The first and senior authors would like to acknowledge the Cognomics Initiative, a joint initiative by researchers of the Donders Centre for Cognitive Neuroimaging, the Human Genetics and Cognitive Neuroscience departments of the Radboud University Medical Center, and the Max Planck Institute for Psycholinguistics in Nijmegen. The Cognomics Initiative has received support from the participating departments and centres and from external grants, that is, the Biobanking and Biomolecular Resources Research Infrastructure (Netherlands) (BBMRI‐NL), the Hersenstichting Nederland, the Netherlands Organization for Scientific Research (NWO), and the European Community's Seventh Framework Programme (FP7/2007–2013) under grant agreements n° 602450 (IMAGEMEND). In addition, the work was supported by a grant for the ENIGMA Consortium (grant number U54 EB020403) from the BD2K Initiative of a cross‐NIH partnership. The POND (Province of Ontario Neurodevelopmental Disorders) data collection was supported by the grant IDS‐I l‐02 (to Evdokia Anagnostou, Jason Lerch) from the Ontario Brain Institute, as well as CIHR support from grants CIHR‐106582, CIHR‐142379 (to Margot Taylor). Initial support for the ENIGMA ADHD and ASD working groups was provided by the U.S. National Institutes of Health Big Data to Knowledge Program (BD2K), under grant U54 EB020403. Joel T. Nigg is supported by an NIH grant R01 MH115357