 Lesch-Nyhan disease LND is an X-linked disorder of purine metabolism which results from mutation in the gene for the enzyme hypoxanthineguanine phosphoribosyltransferase HPRT; patients have hyperuricemia, gout, urinary tract calculi, and nephropathy which are effectively treated with allopurinol. There is also a syndrome of dystonia, chorea and athetosis, as well as involuntary self mutilative biting and aggression toward their caretakers, for which there is no treatment. 