In view of the age differences between the sample studied in this paper, and the sample used in the studies of Wang et al. (2004) and Dick et al. (2007) it is not possible that they should contradict one another. In the Wang et al. (2004) study, about 5% of the alcohol dependent subjects had ages of onset of less than 16 years of age. This is too small a fraction to have an effect on the results. As we noted in our discussion of the trend tests, in our study the genotypic distributions of the alcohol dependent subjects change with age of onset. While we do not observe a significant SNP effect in the oldest age range with DTSA, the fraction of subjects with the minor allele in those who become alcohol dependent is greater than the fraction of subjects with the minor allele in those who do not become alcohol dependent (Fisher’s exact test gives p = 0.07 for the null hypothesis). This trend acts to produce a similar genotypic distributions for alcohol dependent and non alcohol dependent subjects when considered regardless of age of onset.
