What Is rs671 and What Does It Mean for Your Health?

The human genetic code is composed of billions of building blocks, and a slight variation can influence how our bodies function. One such variation is rs671, a well-researched single nucleotide polymorphism (SNP), which is a common change in a single “letter” of our DNA. The presence of the rs671 SNP is linked to the way the body processes certain substances.

This variation is not a rare mutation but a common trait for a significant portion of the global population, particularly those of East Asian descent. This SNP occurs within a gene that directs the production of an enzyme, determining the efficiency of certain metabolic pathways.

The ALDH2 Gene and Alcohol Metabolism

The rs671 SNP is located within the Aldehyde Dehydrogenase 2 (ALDH2) gene. This gene holds the instructions for creating the ALDH2 enzyme, which is produced in the liver’s mitochondria. The primary function of this enzyme is to break down acetaldehyde, a toxic compound that is a byproduct of alcohol metabolism. When alcohol is consumed, it is first converted into acetaldehyde; the ALDH2 enzyme then converts this substance into harmless acetate, which the body can excrete.

The rs671 variation comes in different forms, or genotypes, which directly impact the enzyme’s function. Individuals with the GG genotype have typical and fully functional ALDH2 enzymes. Those with the GA genotype produce an enzyme with significantly reduced activity. People with the AA genotype have a severely deficient or inactive enzyme.

To visualize this, one can imagine a factory assembly line responsible for detoxifying acetaldehyde. The GG genotype represents a line running at full speed, while the GA genotype is like the line running at half speed, causing a backup. The AA genotype signifies a near-complete shutdown of the assembly line, leading to a major accumulation of the toxic compound.

Physical Reactions to Alcohol

The inefficient breakdown of acetaldehyde due to the rs671 variant leads to immediate physical symptoms after consuming alcohol. This set of reactions is known as the “Alcohol Flush Reaction” or, colloquially, “Asian Flush,” because the trait is highly prevalent in people of East Asian descent. The main feature of this reaction is facial redness, but it often includes a wider range of symptoms.

When acetaldehyde accumulates in the body, it causes blood vessels to dilate, resulting in flushing of the face and sometimes the entire body. This buildup is also responsible for other unpleasant effects, such as a rapid heartbeat or palpitations, headache, and nausea. These symptoms are not an allergic reaction but a direct toxic effect of acetaldehyde.

For individuals with the GA or AA genotype, these reactions can occur even after consuming a small amount of alcohol. The intensity of the reaction corresponds to the genotype, and the experience is often so unpleasant that it naturally discourages further alcohol consumption for many with the variant.

Long-Term Health Considerations

Beyond the immediate discomfort of the flush reaction, the accumulation of acetaldehyde carries serious long-term health risks for individuals with the rs671 variant who consume alcohol regularly. The most significant of these is a substantially increased risk of developing esophageal cancer. Acetaldehyde is classified as a carcinogen, and its prolonged contact with the lining of the esophagus can cause DNA damage that leads to cancerous growths.

For those with the GA or AA genotype, drinking alcohol elevates this risk far more than for individuals with the fully functional GG genotype. Studies show a strong gene-environment interaction, where the combination of the genetic predisposition (the rs671 variant) and the environmental factor (alcohol) creates a much greater risk than either factor alone. This makes the rs671 SNP a biomarker for esophageal cancer risk, particularly in East Asian populations.

While the link to esophageal cancer is the most established, research also points to other potential health consequences. The presence of the rs671 variant in drinkers has been associated with a higher risk for other cancers, such as head and neck cancer. There are also emerging connections to an increased risk of gastric cancer and some studies suggest a link to cardiovascular disease.

Beyond Alcohol Metabolism

The ALDH2 enzyme’s role extends beyond processing alcohol. It is a versatile detoxifier that also breaks down other harmful aldehydes the body encounters from sources like air pollution, cigarette smoke, or some foods. The enzyme is a part of the body’s defense system against oxidative stress, which occurs when there’s an imbalance of damaging molecules in cells.

A deficiency in the ALDH2 enzyme, caused by the rs671 variant, means the body is less efficient at clearing these other toxic aldehydes. This can have health implications even for individuals who do not drink alcohol. The reduced ability to manage these compounds may contribute to a higher baseline of oxidative stress.

Research is exploring how ALDH2 deficiency might be connected to conditions beyond those directly related to alcohol. For instance, studies have investigated its potential role in cardiovascular diseases and neurodegenerative disorders like Alzheimer’s disease, where the accumulation of certain aldehydes may play a part.

Interpreting Genetic Test Results

With the rise of direct-to-consumer genetic testing, many people may encounter the rs671 SNP in their own results. Understanding what the different genotypes mean is a practical step toward managing one’s health. Your results will show one of three genotypes—GG, GA, or AA—which correspond to normal, reduced, or severely deficient enzyme function, respectively.

Individuals with the GA and especially the AA genotypes face a significantly higher risk of esophageal cancer if they drink alcohol. A genetic test result is not a diagnosis; it is a measure of predisposition. Lifestyle choices, particularly those related to alcohol consumption, are the most powerful factors in determining the actual health outcome.

For individuals with the GA or AA genotype, the most effective way to mitigate the increased cancer risk is to limit or avoid alcohol. Consulting with a healthcare provider or a genetic counselor is the best course of action to understand personal health risks and develop an informed plan for the future.