Researchers in Taiwan recently found a rare individual, an alcoholic with two copies of the genetic mutation. Think of a person's genetic makeup as a gigantic orchestra. Each of the instruments' notes represents a gene, a protein. Various cell types can combine notes and chords into simple or complex variations. Sometimes the music flows seamlessly, sometimes a wayward note can destroy a certain passage, even the entire concert.
Gene mutations are like discordant musical notes.
There are two enzymes that regulate the metabolism of alcohol. Second, ALDH converts acetaldehyde to acetate. Acetate is then metabolized by tissues outside of the liver. This aversion can manifest itself through cardiovascular complications, hypothermia, nausea, asthma and facial flushing. If there is a genetic mutation of that enzyme, it becomes very inefficient and cannot metabolize acetaldehyde.