That we failed to confirm recent findings from genome-wide studies might stem from the fact that the majority of recent studies reporting positive findings have primarily examined event-related theta power at frontal sites. P3 amplitude consists largely of stimulus-locked activity in the delta and theta frequency ranges (Başar, Başar-Eroğlu, Karaka, & Schürmann, 1999; Kolev, Demiralp, Yordanova, Ademoglu, & Isoglu-Alkaç, 1997), and one might expect some overlap in SNP associations. However, the correlation between frontal theta power and parietal P3 amplitude may not be large enough to be reflected in significant SNP associations. Previous genome-wide findings have also been based on the COGA sample (Chen et al., 2009, 2010; Jones et al., 2006; Kang et al., 2012; Zlojutro et al., 2011), which comprises alcoholic probands and relatives from families with a dense history of alcoholism. Although the density of alcohol dependence in our general population sample is not comparable to its density in COGA, problematic alcohol use is quite prevalent in the MCTFR in general (Hicks, Schalet, Malone, Iacono, & McGue, 2011; McGue et al., 2013), including MTFS twins (Hamdi &
