Red Blood Cells from Individuals with Lesch-Nyhan Syndrome: Multi-Omics Insights into a Novel S162N Mutation Causing Hypoxanthine-Guanine Phosphoribosyltransferase Deficiency

Lesch-Nyhan syndrome (LN) is an is an X-linked recessive inborn error of metabolism that arises from a deficiency of purine salvage enzyme hypoxanthine-guanine phosphoribosyltransferase (HPRT). The disease manifests severely, causing intellectual deficits and other neural abnormalities, hypercoagulability, uncontrolled self-injury, and gout. While allopurinol is used to alleviate gout, other symptoms are less understood, impeding treatment. Herein, we present a high-throughput multi-omics analysis of red blood cells (RBCs) from three pediatric siblings carrying a novel S162N HPRT1 mutation. RBCs from both parents-the mother, a heterozygous carrier, and the father, a clinically healthy control-were also analyzed. Global metabolite analysis of LN RBCs shows accumulation of glycolytic intermediates upstream of pyruvate kinase, unsaturated fatty acids, and long chain acylcarnitines. Similarly, highly unsaturated phosphatidylcholines are also elevated in LN RBCs, while free choline is decreased. Intracellular iron, zinc, selenium, and potassium are also decreased in LN RBCs. Global proteomics documented changes in RBC membrane proteins, hemoglobin, redox homeostasis proteins, and the enrichment of coagulation proteins. These changes were accompanied by elevation in protein glutamine deamidation and methylation in the LN children and carrier mother. Treatment with allopurinol incompletely reversed the observed phenotypes in the two older siblings currently on this treatment. This unique data set provides novel opportunities for investigations aimed at potential therapies for LN-associated sequelae.

NAD metabolism in HPRT-deficient mice

The activity of hypoxanthine-guanine phosphoribosyltransferase (HPRT) is virtually absent in Lesch-Nyhan disease (LND), an X-linked genetic disorder characterized by uric acid accumulation and neurodevelopmental dysfunction. The biochemical basis for the neurological and behavioral abnormalities have not yet been completely explained. Prior studies of cells from affected patients have shown abnormalities of NAD metabolism. In the current studies, NAD metabolism was evaluated in HPRT gene knock-out mice. NAD content and the activities of the enzymes required for synthesis and breakdown of this coenzyme were investigated in blood, brain and liver of HPRT(-) and control mice. NAD concentration and enzyme activities were found to be significantly increased in liver, but not in brain or blood of the HPRT(-) mice. These results demonstrate that changes in NAD metabolism occur in response to HPRT deficiency depending on both species and tissue type.

Expression of purine overproduction in a series of 8-azaguanine-resistant diploid human lymphoblast lines

For study of the basis of an X-linked form of gout in man, several clonal lines deficient in hypoxanthine-guanine phosphoribosyltransferase (EC 2.4.2.8) were selected from the human lymphoblast line WI-L2 by spontaneous and mutagen-induced resistance to 10 muM 8-azaguanine. Three groups could be defined: (1) clones with less than 1% of normal enzyme activity, unable to incorporate [(3)H]hypoxanthine detectable by radioautography, unable to tuilize exogenous hypoxanthine as a source of purines, and showing a 2- to 4-fold accelerated rate of production of early intermediates in de novo purine biosynthesis; (2) clones with 56-63% of normal enzyme activity, decreased incorporation per cell of [(3)H]hypoxanthine measured by radioautography, able to utilize exogenous hypoxanthine, and showing 1.2- to 2.8-fold purine overproduction; (3) clones with 10-15% of normal enzyme activity, able to utilize hypoxanthine but not incorporating amounts detectable by radioautography, and showing a 2.3- to 2.5-fold increase in purine biosynthesis. Resistant clones generated by ICR 191 mutagenesis resembled Group 1 clones. Heat inactivation studies in crude extracts from certain clones in Group 2 suggest a structural gene mutation, but no qualitative alteration in enzyme could be detected by starch gel electrophoresis. These phenotypes have persisted over at least 300 generations of nonselective growth, with retention of a diploid karyotype.