As we stated above, it cannot be assumed that identical risk factors are important in different populations. There are numerous reported instances that show evidence for different linkage signals in different populations (e.g., genetic linkage studies of cocaine and opioid dependence that we have reported previously, 23, 24). There are also instances where specific risk alleles differ by population. One such instance – where it has been shown that a specific risk allele is present in AAs but not EAs – involves ADH loci and risk for alcohol dependence. ADH2 rs2066702, traditionally called Alcohol Dehydrogenase-2*3, is a functional variant that encodes a high-activity isozyme that is common in AAs but rare in EAs (38). According to the observations of several authors, including ourselves (39), this is a risk variant. (We observed minor allele frequencies for this variant of 0 in EAs, 0.178 in AD AAs, and 0.255 in AA control subjects (39).)
