In terms of the methodology, DTSA requires that there be differences in genotypic distributions between alcohol dependent and non alcohol dependent subjects to give a statistically significant results for a SNP; this is not true for the family based method (pedigree disequilibrium test) used by Wang et al. (2004). (In that study there is no difference in genotypic distribution between the alcoholic and non-alcoholic subjects.) Our interpretation is that family based studies are more powerful than the type of association study employed here; the absence of a distributional difference does not mean that there is no genetic effect.
