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The Genetics of Asian Flush

By Justin Zhou

Sometimes when you finish an alcoholic drink, you feel a sudden rush of blood streaming upwards throughout your entire body making your entire face feel warm and beaming red; sometimes it's not only your face but your arm and neck as well, that cherry color and puffiness that is all too familiar. Such a reaction that your body has towards alcohol is termed alcohol flush, and in context of the Asian population it is more widely known as the Asian flush or the Asian glow. It comes to no surprise that it derives its name by having those of Asian descent being more commonly exposed to such experiences. But why is such an effect and syndrome so much more prevalent in the Asian community compared to others? This is because of one or more gene deficiencies where one or more enzymes do not work properly when breaking down the alcohol (ethanol), through evolutionary means, ingrained in themselves.

Upon consummation of alcohol the body begins to breakdown its molecular components, and the two main enzymes responsible for such process are alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH). The two enzymes help maintain balance within our body by initiating a multistage breakdown process to eliminate toxins, protecting us from the harmful byproducts. First, the ADH enzyme first breaks down the alcohol (ethanol) and converts it into the toxin acetaldehyde, in which after, the ALDH enzyme converts the toxin into less harmful compounds known as acetate. Such conversion allows other biochemical interactions within the body to easily turn the acetate into water and CO2 and allow it leaves the system. Class I alcohol dehydrogenase sequence polymorphism (ADH1B rg47His) is a gene that regulates the production of ADH which as for mentioned before facilitate alcohol breakdown. Recent studies have shown that the emergence of agriculture about ten-thousand years ago possibly increased polymorphic selection for this gene. Selection for the gene is caused by the need for our body to signal that excess alcoholic content is consumed due to its residue from one of the first cultivated crops.

In Southern China, gene set enrichment analysis of the ADH1B gene suggest positive selection on this genetic locus during Neolithic times. Genetic evidence of the selection on the ADH1B polymorphism suggested a dietary shift in agricultural societies that possibly impacted the genetic makeup of these Neolithic human populations, is caused by the emergence and expansion of rice domestication in East Asia. Furthermore, geographic distribution of the ADH1B allele in East Asia is consistent with the unearthed culture relic sites of rice domestication in China. Additionally, the estimated origin time of ADH1B allele in those populations coincides with the time of origin and expansion of Neolithic agriculture in southern China (Peng et al., 2010).

It has been found that more than 36% of East Asians, primarily Koreans, Japanese, and Chinese people, suffer from Asian Flush (Brooks et al., 2009). Aforementioned, the gene anomaly developed where the functionality of the above-mentioned enzymes are impaired causes the inability for people to ingest large amounts of alcohol without showing the previously-said symptoms. Evolutionary speaking, the gene developed in a way to discourage people from drinking too much, preventing the rise of alcoholism. Such a selection introduction of alcohol into society consequently a new compound for the body, this physical substance in which we are in developing its own defense mechanism to protect ourselves from harm.

So the next time you pick up your favorite alcoholic drink and you turn beet red, thank your evolutionary genes, because they might have saved you and your lineage all those millennium before.

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