An additional criterion of an endophenotype is that it should be present in individuals whose genetic makeup is similar to those with the manifest disorder even if the disorder is absent. Studies of beta power in first-degree relatives of alcohol-dependent individuals have yielded mixed results. Increased beta power has been observed in high-risk offspring (Bauer & Hesselbrock, 1993; Rangaswamy et al., 2004) as well as other relatives of alcoholics (Pollock, Earleywine, & Gabrielli, 1995), although this is sometimes limited to subjects of one gender (Propping, Kruger, & Mark, 1981), to subjects with comorbid antisocial behavior (Bauer & Hesselbrock, 1993), or to one way of measuring power (Finn & Justus, 1999). There have also been reports of null findings (Cohen, Porjesz, & Begleiter, 1991; Kaplan, Hesselbrock, O’Connor, & DePalma, 1988; Pollock et al., 1983), and reports of reduced alpha power rather than increased beta power (Ehlers & Schuckit, 1991; Finn & Justus, 1999). Alcohol ingestion has been found to result in greater beta power increases in high-risk individuals relative to low-risk individuals (Ehlers & Schuckit, 1990), supporting the notion that there is a familial component to increased beta activity, albeit one that may interact with exposure to alcohol.
