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Until recently, no one could imagine a genetics-first study of the size and depth described in this issue of JAMA Psychiatry by D’Angelo and colleagues.1 The more familiar phenotype-first approach defines affected individuals based on DSM or other criteria and then looks for genetic risk variants. Based on this approach, rare genomic variants, including copy number variants (CNVs) such as 16p11.2 duplications and deletions, have been identified as significant risk factors in autism spectrum disorder (ASD), intellectual disability, and schizophrenia, albeit each variant in a small fraction of individuals.2 Because these phenotypes are individually rare, trying to understand them in association with a genomic variant within the clinically defined (phenotype-first) population used to define its contribution to risk is impractical.3
Lord C, Veenstra-VanderWeele J. Following the Trail From Genotype to Phenotypes. JAMA Psychiatry. 2016;73(1):7-8. doi:10.1001/jamapsychiatry.2015.2344