The cytosolic ALDH1 enzyme also contributes to the elimination of acetaldehyde, helping to control acetaldehyde levels even in people with the ALDH2*2 allele. Several promoter polymorphisms in the ALDH1A1 gene affect gene expression in vitro (Spence et al. 2003). However, these alleles only occur at low frequencies, and their impact on alcoholism risk still is controversial. One study in Southwest California Indians found that people carrying an ALDH1A1*2 allele had lower rates of alcohol dependence and lower maximum number of drinks ever consumed in a 24-hour period (Ehlers et al. 2004). In contrast, in an Australian community-based sample, ALDH1 enzyme activity in blood cells was not associated with alcoholism or the reaction to alcohol (Hansell et al. 2005). This discrepancy in findings could result from the fact that promoters and variations within them act differently in different cell types and that activity levels in blood cells therefore may not reflect activity levels in the liver.
