hereditary metabolic disorder affecting the central nervous system and characterized by incoordination, mental retardation, aggressive behaviour, and compulsive biting. The cause of the syndrome is a defective organic catalyst or enzyme, hypoxanthine-guanine-phosphoribo-syltransferase, which normally is particularly active in brain cells and is involved in the metabolism of purines. The Lesch-Nyhan syndrome is transmitted by a recessive sex-linked gene, affecting chiefly males, and it is possible to detect it before birth in the offspring of women known to be carriers of the trait.