Results indicated that there was substantial genetic influence on each of the endophenotypes and that each was highly heritable – to a similar degree in males and females. These results are consistent with previous reports on heritability estimates of and genetic influences on the individual ERP and EEG measures and EXT (e.g. Begleiter & Porjesz, 2006; Hicks et al., 2007; van Beijsterveldt & Boomsma, 1994; van Beijsterveldt et al., 1996). Extending these findings, we also demonstrated that these three endophenotypes 1) show significant negative phenotypic and genetic correlations with a general vulnerability to EXT disorders, 2) show modest to strong phenotypic and genetic correlations with each other, and 3) are sensitive to genetic effects that may differ as a function of gender. These relationships suggest that these three endophenotypes are likely tapping into neurophysiological processes and genes that are both common across them and unique to each – all of which are relevant to a biological vulnerability to EXT psychopathology.
