Rosey Cheeks from a Glass of Wine?

Do you look like you are blushing after drinking a glass of wine or beer? I know my face gets pretty flushed within those first couple of drinks. This characteristic happens to indicate part of your genotype. Depending on the genes you possess, you may be more or less susceptible to the affects of alcohol.
After consumption of alcohol, the alcohol dehydrogenase enzyme (ADH) works to break down the ethanol into acetaldehyde inside your liver (Kim et. al, 2005). Another enzyme known as aldehyde dehydrogenase-2 (ALDH2) then turns the acetaldehyde into acetic acid (Kim et. al, 2005). Acetaldehyde is the toxic byproduct of ethanol which the enzymes in the liver work to detoxify. In some cases, a mutation occurs in the ALDH2 gene where there is a substitution of a nucleotide pair (Kim et. al, 2005). The nucleotide goes from a G to an A and results in an amino acid change from Glutamine to Lysine which causes a loss of function of ALDH2 (Kim et. al, 2005). People with this mutant gene experience flushing of the face, tend to get sick, have headaches, or sweat after ingesting alcohol (Kim et. al, 2005). The build-up of acetaldehyde in the tissues and the body's inability to convert this toxin to acetic acid due to lack of ALDH2 activity causes these sickening symptoms. It has been found that many people of Asian descent possess this mutated ALDH2 genotype which is why they tend to have a much lower alcohol tolerance than people of different nationalities. Kim et. al (2005) looked into whether there may be more to the genotype than either having a fully active gene or a completely inactive gene. They believe that the ALDH2 activity could be a result of inheritance from both parents. In this case, a range of genotypes could occur where some people are homozygous for normal ALDH2, some are heterozygous (1 normal ALDH2 and 1 mutated ALDH2), and some homozygous for the defective ALDH2 (Kim et. al, 2005). Kim et. al, (2005) performed a study where they looked at people with each of these genotypes and measured whether alcohol intake resulted in a flushed face. After drinking one beer, 6.5% of the people with active ALDH2, 92.3% of heterozygotes of ALDH2, and 100% of homozygotes for the defected ALDH2 gene all demonstrated flushed faces (Kim et. al, 2005). The study showed the variation in phenotypes as a result of differing genotypes and that each genotype corresponds to a different level of ALDH2 activity (Kim et. al, 2005). Although complete inactivity of ALDH2 is commonly found in people of Asian background, members of other origins may exhibit decreased acetaldehyde detoxification as a result of a heterozygous genotype.
Next time you are drinking, look into the mirror after you first glass of alcohol. A red face may indicate that your body isn't getting rid of the acetaldehyde as fast as it should, and that it may be building up in your blood and tissues. Your visible phenotype may be a signal to what your genotype is and prevent you from drinking more alcohol than your body can tolerate.