Lesch–Nyhan Syndrome is a rare X-linked disease characterized by hyperuricemia, gout, dystonia, microcephaly, mental retardation, and self-injurious behavior, and is caused by the hypoxanthine-guanine phosphoribosyltransferase (HPRT1) enzyme deficiency and altered purine metabolism. The gene discussed is HPRT1; the disease is X-linked disease.