this mutation) produce an ALDH enzyme with extremely low enzyme activity (Crabb et al. 1989). As a result, these individuals exhibit highly elevated levels of acetaldehyde, which produces aversive reactions, including flushing, elevated heart rate (i.e., tachycardia), and nausea after consuming even a small amount of alcohol (Eng et al. 2007). Similarly, coding variations in the ADH1B gene (called ADH1B*2 and ADH1B*3) that encode highly active enzymes which increase the rate at which acetaldehyde is produced also are strongly protective and reduce the risk for alcohol dependence (Edenberg 2007; Thomasson et al. 1991).
