Hill and colleagues (1999), extrapolating from growth curves describing trajectories of change in P3 amplitude among high- and low-risk youth, estimated that the curves would converge at some point in the early twenties. Because P3AR is also associated with substance abuse, they proposed that early in development it serves as an endophenotype but later reflects neurotoxic effects of substance use. In the Carlson et al. (2007) study of high and low risk young men between 17 and 24 years of age, the convergence predicted by Hill and colleagues was not observed. Nevertheless, the magnitude of P3AR among high-risk subjects at 24 was less than at 17, and the high and low risk groups differed little after age 20. Carlson and Iacono’s (2006) previous study reported that cross-sectional estimates of P300 heritability were smallest among the 24-year-old subjects. Taken together, these findings suggest that the utility of P3AR as an endophenotype may be developmentally limited.
