Variant:

rs975833 at chr4:100201739 in ADH1A (VIP)

Appendix

ADH1A is part of a gene cluster of alcohol dehydrogenase enzymes on chromosome 4 [Article:16685648]. Some haplotype blocks extend across multiple genes in this region [Article:16685648]. Two recent studies have examined the potential association of diplotypes of ADH1A and other genes in the alcohol dehydrogenase gene cluster on alcohol dependence (AD) [Article:16685648] and Drug Dependence (DD) [Article:17185388]. For the purposes of their article, the authors defined DD as being either cocaine or opioid dependence. The authors used a relatively new statistical technique called diplotype trend regression (DTR) which has many advantages over other commonly used statistical tests [Articles:16685648, 17185388].

A diplotype is basically a genotype that consists of two haplotypes. In the case of ADH1A, the authors genotyped for three marker positions [Articles:16685648, 17185388], and therefore each diplotype consisted of six bases, three on one chromosome, and three on the other. Of the three markers that the authors used to genotype for ADH1A, only ADH1A^SNP11 was located in an intron or exon; the other two markers were flanking the gene, with one upstream, and one downstream [Articles:16685648, 17185388]. The authors found several diplotype combinations that were associated with increased risk for alcohol dependence in their European American sample (AGA/TGA, AGA/TCG, AGA/AGA, TCG/TGA, AGA/TGG, TGA/TGA, TCG/TGG, TGA/TGG, TCG/TCG) [Article:16685648]. Interestingly, two diplotype pairs in the African American sample were found to be protective against alcohol dependence (TCG/TCG, TGA/TGA) [Article:16685648]. This finding is likely explained by the fact that the authors also discovered that ADH1A was found in different LD blocks in the European American and the African American populations [Article:16685648]. In a later study, the authors found similar results when they applied DTR to associate the ADH markers with DD [Article:17185388].