On pages 58-60 Dr. Sharon Moalem talks about the issues that some individuals of Asian descent have with their body's response to alcohol. This connects to BIG Idea 3, which states "Living systems store, retrieve, transmit, and respond to information essential to life processes." The cause for this reaction is the genetic variant, (ALDH2*2) that produces a less powerful form of acetaldehyde dehydrogenase.
Describe how the body detoxifies alcohol and why the ALDH2*2 gene would be less helpful for doing these tasks. In addition, talk about the positive effects of possessing this gene and why the evolution of Asian populations make them more commonly prone to this gene, connecting back to natural selection by comparing the environments of different populations. Finally, research the the locus of the gene, as well as the way that doctors are trying to use this gene to treat alcoholics, and the methods that they are using to do so (what types of medicine, how it is taken, etc.).
Patrick Austin (email: paustin4@students.d125.org)
When a person drinks alcohol, their body detoxifies it using multiple different enzymes and organs (especially the liver). First, the enzyme alcohol dehydrogenase converts the alcohol into acetaldehyde. Then, the enzyme acetaldehyde dehydrogenase converts acetaldehyde into acetate. After that, acetate is converted into fat, carbon dioxide, and water. The reason people with the ALDH2*2 gene cannot drink alcohol without experiencing the flush response is that this gene produces a less powerful form of the acetaldehyde dehydrogenase. This weaker form is much less effective in converting acetaldehyde into acetate. Since acetaldehyde is 30 times more toxic than alcohol, it produces strong reactions, including the flush response (pg. 59). One benefit to possessing this gene, however, is that people with the ALDH2*2 gene are very unlikely to become alcoholics since they can’t even drink alcohol without experiencing the unpleasant flush response as well as bad hangovers (pg. 59).
ReplyDeleteNatural selection due to environmental pressure can explain why the ALDH2*2 gene is so prevalent in Asian populations but very rare in Europeans. When humans started living in cities and towns, clean water was one of the biggest problems facing cities since sanitation and taking care of waste was not efficient—they had no modern plumbing. In Asia, water was purified because it was boiled to make tea. However, in Europe, people used fermentation because the alcohol created killed bacteria and microbes when mixed with water. Therefore, there was an environmental pressure in Europe to be able to effectively detoxify alcohol because it was in the water that people drank every day. However, in Asia, there was very little pressure, allowing the ALDH2*2 gene to stay prevalent in the gene pool (pg. 60).
The ALDH2*2 gene is located on Chromosome 12; the “address” is 12q24.2 (http://www.ncbi.nlm.nih.gov/gene/217). The properties of this gene are being used to find methods to treat alcoholics because people with this gene are so resistant to alcoholism. One drug used is called disulfiram, and it mimics the effect of the ALDH2*2 gene. The drug works by lessening the body’s supply of acetaldehyde dehydrogenase enzymes, so the body is not as effective at converting acetaldehyde into acetate. The result is that people who take this drug and drink alcohol have a response similar to Asian flush (pg. 59-60). Therefore, taking the drug steers people away from drinking because of the unpleasant effects. Disulfiram is fairly simple to take: it comes in tablets that should be swallowed once a day or that can be crushed and mixed with water or other drinks (http://www.nlm.nih.gov/medlineplus/druginfo/meds/a682602.html).
(Sanika Bhargaw, sbharga4@students.d125.org)