Every characteristic of human anatomy and physiology is determined by biochemical reactions catalyzed by enzymes. These in turn are determined by our genetic make-up. If a gene is defective or missing it will result in a defective or missing enzyme, a so-called "inborn error of metabolism." Knowledge of the defective enzyme and its gene(s) may well make possible the rational treatment of the resulting disease. The Inborn Errors of Metabolism Map identifies the site of over 100 metabolic deficiency diseases which are named on the sides of the map.