Aldehyde dehydrogenase 2 family (mitochondrial), also known as ALDH2, is a human gene found on chromosome 12. Two major liver isoforms of this enzyme, cytosolic and mitochondrial, can be distinguished by their electrophoretic mobilities, kinetic properties, and subcellular localizations. The ALDH2 gene encodes a mitochondrial isoform, which has a low Km for acetaldehydes, and is localized in mitochondrial matrix. Most Europeans have two major isozymes, while approximately 50% of Northeast Asians have one normal copy of the ALDH2 gene and one mutant copy that encodes an inactive mitochondrial isoenzyme. A remarkably higher frequency of acute alcohol intoxication among Northeast Asians than among Europeans has been repeatedly shown to be related to the very much reduced activity of the mutant ALDH2-2 isoenzyme.