There are three known functional variants of the ADH1B enzyme (β-ADH), the cytosolic alcohol dehydrogenase at highest concentration in adult liver20, 29. The reference allele, with a frequency of over 95% in populations of European descent, is generally known as ADH1B (ADH1B*1; known as ADH2*1 in the older literature†), and encodes an enzyme (β1–ADH) with arginine at positions 48 and 370. ADH1B*48His (ADH1B*2; rs1229984) encodes β2–ADH, with a histidine at position 48, and ADH1B*370Cys (ADH1B*3; rs2066702) encodes β3–ADH with cysteine at position 370. The enzymes encoded by ADH1B*48His and ADH1B*370Cys metabolize ethanol in vitro at 30-40-fold higher rates than does β1–ADH20, 29. A Japanese study of individuals checking into a hospital the day after heavy drinking showed that those with two copies of ADH1B*1 had higher blood alcohol concentrations than did those with at least one copy of ADH1B*48His, indicating that there is a measurable effect in vivo30. Although some individuals with the ADH1B*48His allele report flushing upon consuming alcohol, it does not approach the dramatic Asian flushing reaction caused by the ALDH2*504K allele, nor does it lead to the
