As Table 2 shows, the degree to which our candidate endophenotypes were heritable had little discernible consequence. Their heritability ranged from virtually 0 to greater than .80, but the results did not vary appreciably. One endophenotype consisted of a P300 factor score that, because it captured the genetic covariance across multiple electrodes, had a heritability of 1.00. Despite this refinement to optimize capture of genetic variance, the genetic factor afforded no apparent advantage over other measures. Of note, even if genetic influences on a trait account for only a small fraction of trait variance, there is no reason why an adequately powered GWAS would not identify variants associated with what genetic effect exists. The crucial issue seems to be the genetic “architecture” of these electrophysiological endophenotypes. Our findings are consistent with a conclusion that they represent polygenic traits influenced by many genetic variants.
