The Lesch-Nyhan (LN) syndrome is an X-linked recessively inherited disease caused by a total deficiency of hypoxanthine guanine phosphoribosyltransferase which is characterized by mental retardation, choreoathetosis, self mutilating behavior, and hyperuricemia. A wide variety of mutations at the HPRT locus has been described in patients with this clinical phenotype. The origin and mechanisms of mutations causing the disease are poorly understood. In this continuing research effort, we propose to develop new simplified nucleic acid-based methods for detecting and characterizing mutations in patients and female carriers of the disease. The complete nucleotide sequences of the mouse and human HPRT genes will be deter mined. Comparison of these sequences will identify conserved regions within and flanking the gene which may have important biological functions. In addition, the human sequence will facilitate analysis of LN mutations at the nucleotide level. The relationship between HPRT deficiency and the neurological symptoms observed in LN syndrome is also poorly understood. While the LN syndrome is a single gene defect, other enzymes in the purine metabolic pathway may play a role in the pathophysiology of the disease. We propose to obtain cDNA and genomic clones for several candidate enzymes of this pathway. These sequences will be used to generate transgenic mice deficient in these enzymes by antisense RNA inhibition of endogenous gene expression. Such animals may provide insight into the role of purine metabolite levels in inducing the neuropathological state. Metabolic inhibitors of these enzymes will also be used in an attempt to induce LN symptoms in HPRT-deficient mice. The successful execution of these proposed studies will further our knowledge of the HPRT gene structure and its mutational events, and have broader applications to the study of other genetic diseases, particularly those caused by new mutation. Furthermore, the production of mouse models of human diseases of the purine metabolic pathway will increase our understanding of the pathophysiology of the diseased state and facilitate corrective measures.