If you happen to be Asian, you might have noticed a difference in your playful drinking habits compared to other ethnicities. Still, it's summer and you want to enjoy your last few days carefree! So you go out and have a beer with your buddies. You feel a flush creeping over your face. After a few more drinks, your face turns noticably red and perhaps it is brought up by your good natured friends. You persist in alcohol consumption and you start to feel nauseous. A few hours later, you excuse your self to the bathroom as best as an intoxicated person can. Your dinner takes a shortcut to the toilet.
"Oh, I'm allergic to alcohol..." you might say. The flushing reaction, the nausea, vomiting and headache sound like good symptoms.
Not quite. You actually have a mitochondrial enzyme deficiency in "ALDH2." What is that? Well, alcohol is absorbed in your stomach and your liver starts grinding away at it with alcohol dehydrogenase (ADH.) The byproduct of this reaction is acetaldehyde. In most people, this acetaldehyde is converted into acetate with the enzyme aldehyde dehydrogenase (ALDH.) However, some asian people lack this enzyme and the aldehyde builds up. The high concentration of aldehyde (along with alcohol) builds up in the blood, leading to those unpleasant feelings that other people might get after having 10x as much alcohol.
The fact that this is a "mitochondrial enzyme" made me wonder if this meant that you could blame your mom for your intolerance to alcohol. After all, you inherit all of your mitochondria from the parent that bore you into the world. I poked through a few scientific journals on PubMed. I learned that it was a dominant allele (meaning that your parents are much more likely to pass on to you and affect you.) ALDH is active in mitochondria AND the rest of the cell (likely by ALDH1 or something like that)... so you actually clear acetaldehyde slowly... and your dad might be to blame.
"Why would evolution punish me so?!?" you might ask, being afflicted with this horrible, party-pooping disability that cripples your now-withering social life. Well, there's a theory that it has to do with cancer. HepB is a sexually-transmitted virus that you can get from your mom at birth if she has it -- and a lot of women in Asia have this virus. HepB greatly increases your chance for liver cancer. Drinking adds to this risk by causing liver damage and cirrhosis, so having ALDH2(2) might be a historic marker helping to prevent cancer! Nowadays, we have a vaccine that prevents Hepatitis B, as I've mentioned before.
If that is not enough for you, be glad that it prevents alcohol toxicity, which can lead to serious problems like blackouts, coma and death. You just get minor aldehyde toxicity instead. Just remember, there's a reason why it is called inTOXICation.
Crabb, DW. Genotypes for aldehyde dehydrogenase deficiency and alcohol sensitivity. The inactive ALDH2(2) allele is dominant. J Clin Invest. 1989 Jan;83(1):314-6. PMID: 2562960
Jenkins, WJ. Subcellular localization of acetaldehyde dehydrogenase in human liver. Cell Biochem Funct. 1983 Apr;1(1):37-40.
Lin, YP. Why can't Chinese Han drink alcohol? Hepatitis B virus infection and the evolution of acetaldehyde dehydrogenase deficiency. Med Hypotheses. 2002 Aug;59(2):204-7. PMID: 12208210