The ADH1B gene provides instructions for making alcohol dehydrogenase 1B (ADH1B), an enzyme that is part of a larger family of alcohol dehydrogenases. These enzymes are involved in the body’s metabolic pathways, processing various substances, including alcohols.
The Role of ADH1B in Alcohol Processing
The ADH1B gene plays a specific role in the initial step of alcohol metabolism. The enzyme it produces, ADH1B, is responsible for converting ethanol into a compound called acetaldehyde. This conversion is a primary pathway for ethanol degradation in the human body.
This metabolic process largely takes place in the liver, where ADH1B activity is notably high. The enzyme facilitates the removal of hydrogen from ethanol, leading to the formation of acetaldehyde. Acetaldehyde is a reactive and potentially harmful compound, making its rapid processing by the body important.
Following the initial breakdown by ADH1B, acetaldehyde is further metabolized into acetate, a less toxic substance. This subsequent step is carried out by another enzyme, aldehyde dehydrogenase 2 (ALDH2), which provides a complete metabolic pathway for alcohol elimination.
Genetic Variations and Their Impact
The ADH1B gene exhibits common genetic variations, known as polymorphisms, which influence the activity of the ADH1B enzyme. Two notable alleles are ADH1B2 and ADH1B3. These specific variations result in different enzyme efficiencies for breaking down ethanol.
The ADH1B2 allele, also identified as rs1229984, leads to a significantly faster conversion of ethanol to acetaldehyde compared to the more common ADH1B1 variant. Similarly, the ADH1B3 allele, also known as rs2066702, encodes an enzyme subunit with a substantially greater turnover rate for ethanol. This increased enzyme activity means that individuals carrying these variants produce acetaldehyde more rapidly after consuming alcohol.
The faster production of acetaldehyde can lead to its quicker accumulation in the body, as the subsequent enzyme, ALDH2, might not be able to process it quickly enough. These genetic variants show distinct patterns of prevalence across different populations. The ADH1B2 allele is particularly common in East Asian populations, with frequencies as high as 73.9%. It is also found in some Middle Eastern populations but is rare in Western and Central Europeans, where its frequency is around 3.8%. The ADH1B3 allele is predominantly observed in populations of African descent and certain Native American tribes.
Health Implications of ADH1B Variations
Genetic variations in ADH1B can lead to immediate physiological responses upon alcohol consumption. For instance, individuals with fast-acting ADH1B variants, such as ADH1B2, often experience the “alcohol flush reaction”. This reaction is characterized by symptoms like facial redness, nausea, and an increased heart rate, which occur due to the rapid accumulation of acetaldehyde in the bloodstream. This unpleasant response can serve as a deterrent to heavy alcohol consumption.
The uncomfortable symptoms associated with these fast-acting ADH1B variants offer a protective effect against alcohol use disorder (AUD). Carriers of the ADH1B2 allele, for example, tend to consume less alcohol and have a reduced risk of developing alcohol dependence.
Conversely, certain ADH1B genetic variants can influence the risk of specific alcohol-related health conditions. Prolonged exposure to acetaldehyde, which can occur with slower ADH1B activity or less efficient ALDH2, is linked to an increased risk of certain cancers, including esophageal cancer, head and neck cancer, gastric cancer, and potentially bladder cancer. While ADH1B plays a role in alcohol metabolism and its associated health outcomes, the overall effects are complex and involve interactions with other genes and environmental factors.