Lesch-Nyhan syndrome, hereditary metabolic disorder, affecting the central nervous system. First described in 1964 by William Nyhan and Michael Lesch, it is caused by a defective enzyme hypoxanthine-quinine-phos-phoribasyl-transferase, which is normally very active in brain cells. It is characterized by mental retardation, aggressive behavior and a tendency to inflict self injury. The syndrome is transmitted by a recessive sex-linked gene and primarily affects males. There is no cure or effective treatment.