In the present report, we explored a multivariate approach to identifying electrophysiological endophenotypes related to EXT psychopathology, using a large sample of male and female adolescent twins and measures identified in the literature as promising individual endophenotypes for EXT. The P3 ERP, its associated TF components, and beta frequency resting state EEG have each shown promise as endophenotypes for various disinhibitory disorders in the EXT spectrum and/or a general EXT factor. Using composite measures and fitting multivariate biometric Cholesky models, we specifically addressed the following aims: 1) assess the magnitude of the phenotypic and genetic associations between each endophenotype and EXT, 2) determine if there is significant shared genetic variance among the multiple endophenotypes and EXT, 3) determine if any of the endophenotypes share unique genetic variance with EXT (i.e. variance which is not also shared with the other endophenotypes), and 4) explore potential gender differences.
