Adenine phosphoribosyltransferase partial HGPRT deficiency

Increased intracellular levels of PP-ribose-P have been implicated in the cause of certain hyperuricemic states associated with uric acid overproduction. Fibroblasts from two patients with the Lesch-Nyhan syndrome were found previously to have an elevated intracellular concentration of PP-ribose-P with a normal rate of PP-ribose-P production (Rosenbloom, et al., 1968). Green and Seegmiller (1969) subsequently reported a mean PP-ribose-P value of 47.1 in erythrocytes from seven patients with HGPRT deficiency. We have confirmed these elevated PP-ribose-P levels in three additional patients with the Lesch-Nyhan syndrome with values of 20.5, 39.4 and 49.5 juM (Table 1). The mothers of these patients are obligate heterozygotes and have normal PP-ribose-P levels. Two diseases associated with a deficiency of other PRT enzymes are not associated with altered erythrocyte PP-ribose-P levels (Table 1). PP-ribose-P levels were in the normal range in one patient with a partial deficiency of adenine phosphoribosyltransferase (APRT) and in one patient with orotic aciduria, which is due to a deficiency... 

Partial deficiency of HGPRT, a salvage enzyme of purine metabolism, has been demonstrated to be the primary abnormality causing purine overproduction in a small proportion of patients with gout (l-4). The quantitative deviation in the activity of this enzyme has been shown by Kelley et al. to be associated with decreased stability to thermal inactivation (2). These authors suggest that in the affected subjects HGPRT is structurally altered. Furthermore, in some of these patients erythrocyte adenine phosphoribosyltransferase (APRT) activity was found to be increased and relatively thermostable (2). 

Adenine phosphoribosyltransferase activity assayed by an analogous method using 0.6 mM adenine-8-l C (specific activity 4 mCI/mmole) was not significantly altered in any of the HGPRT-deficient clones (Table II). Starch gel electrophoresis using a method only slightly modified from that of Watson et. al. (19) showed no difference in electrophoretic mobility of mutants partially deficient in HGPRT (Fig. 3) but could not be used to examine the clones with severely deficient enzyme activity. 

Recent advances in the understanding of human purine metabolism have been stimulated by the discovery of specific inborn errors of this pathway in man. In particular, the demonstration of the deficiency of hypoxanthine-guanine phosphoribosyltransferase (HGPRT) in the Lesch-Nyhan syndrome and in some patients with gout has contributed essential information on the regulation of purine biosynthesis novo and on the critical role of this reutilization pathway in central nervous system function in man. The search for other disorders led to the description of a partial deficiency of adenine phosphoribosyltransferase (APRT) in four members in three generations of one family. Each of the subjects partially deficient in APRT exhibited a normal serum urate concentration and the propositus had a normal excretion of uric acid (Kelley, et al., 1968). We have investigated a second family partially deficient in APRT (Fox and Kelley, in press). 

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