There have been only a few twin studies of the P50 gating phenotype. Two earlier studies estimated twin correlations but did not provide formal heritability estimates, perhaps due to small sample size. One study found a .57 correlation in MZ and 0 in DZ twins (Young et al., 1996), while the other study reported intrapair correlations of .50 and .13 for MZ and DZ, respectively (Myles-Worsley et al., 1996). Another small-scale twin study suggested that the extent of alcohol-induced reduction in P50 suppression effect is a stable trait influenced by genetic factors (Freedman et al., 1987). A more recent study using 40 MZ pairs and 30 DZ pairs found intrapair twin correlations of .52 and .04 for MZ and DZ, respectively and estimated heritability at 68%.using the structural equations modeling (SEM) approach. However, another study (Anokhin et al., 2007b) based on a larger twin sample and using alternative methods for P50 quantification found substantially lower but significant heritability of P50 gating (27-36%, depending on the method for P50 measurement). The same study investigated the gating effect in relation to the
