[Properties of hypoxanthineguanine-phosphoribosyltransferase (HGPRTase) in a gout patient with partial deficiency of this enzyme (author's transl)]

A molecular survey of hypoxanthine-guanine phosphoribosyltransferase deficiency in man

We characterized 24 unrelated patients with a deficiency of the enzyme hypoxanthine-guanine phosphoribosyltransferase (HPRT) in an attempt to better understand the nature and spectrum of mutations that underlie this prototype-inherited disease. Lymphoblast cell lines derived from each patient were analyzed at multiple molecular levels including the structure and function of the residual HPRT enzyme, messenger RNA (mRNA), and gene. Our studies demonstrate the following: (a) at least 16 of the 24 patients represent unique and independent mutations at the HPRT structural gene; (b) the majority of cell lines have normal quantities of mRNA but undetectable quantities of enzyme; (c) 33% of patients retain significant quantities of structurally altered, functionally abnormal, HPRT enzyme variants; and (d) a minority of patients are void of both enzyme and mRNA, possibly representing examples of aberrations in gene expression. Our studies provide direct evidence for marked genetic heterogeneity in this disorder and illustrate the kinds of mutations and mutational consequences that underlie inherited disease in humans.

Human hypoxanthine-guanine phosphoribosyltransferase. Demonstration of structural variants in lymphoblastoid cells derived from patients with a deficiency of the enzyme

We have explored the possibility of using cultured lymphoblasts from patients with a deficiency of hypoxanthine-guanine phosphoribosyltransferase (HPRT) as a source of cells for the isolation and characterization of mutant forms of the enzyme. HPRT from lymphoblasts derived from six male patients of five unrelated HPRT-deficient families was highly purified and characterized with regard to: (a) level of immunoreactive protein, (b) absolute specific activity, (c) isoelectric point, (d) migration during nondenaturing polyacrylamide gel electrophoresis, and (e) apparent subunit molecular weight. There experiments were performed on small quantities of lymphoblasts using several micromethods involving protein blot analysis of crude extracts as well as isolation and characterization of enzyme labeled in culture with radioactive amino acids. The lymphoblast enzymes from four of the patients exhibited structural and functional abnormalities that were similar to the recently described abnormalities found with the highly purified erythrocyte enzymes from these same patients. In addition, a previously undescribed HPRT variant was isolated and characterized from lymphoblasts derived from two male siblings. This unique variant has been called HPRT Ann Arbor. We conclude that lymphoblastoid cell lines can be used as a source of cells for the detection, isolation, and characterization of structural variants of human HPRT.