Lesch-Nyhan syndrome, also known as juvenile gout, is a rare X-linked disorder of purine metabolism that affects multiple organ systems. The defective enzyme is hypoxanthine-guanine phosphoribosyltransferase (HGPRT). Patients develop primary hyperuricemia from oversynthesis of uric acid. Males are more commonly affected than females.

Phenotype is largely dependent on degree of enzyme deficiency; those most affected have the classic triad of dystonia, spasticity, and self-injurious behavior. Self-mutilating behavior, particularly biting, is distinctive; fingers and lips are common targets. Renal complications develop first, within the first several months of life. Cutaneous findings can mimic gout, with painful inflammation of joints and multiple tophi. Poor muscle control and developmental delay can be noticed in the first year of life. During the second year, self-mutilating behavior including lip and finger biting can be noticed.