Our goal was to capitalize on the genetic architecture of externalizing spectrum disorders to identify molecular genetic influences that these disorders share. To do this, we conducted a family-based genome-wide association study of an externalizing score in a predominantly clinically ascertained sample. We identified 3 independent genome-wide significant loci from the meta-analysis of the European and African ancestry groups in COGA. However we did not find evidence for replication of these loci and we did not discover any robust genome-wide significant signals or polygenic associations. We also note that supplementary analyses using an alternative linear mixed modeling approach, where all populations are analyzed together with principal components and a genetic relatedness matrix (GRM) to adjust for population stratification (Sul et al., 2018; Wojcik et al., 2019), produced highly similar results (supplementary information, Section 3).
