J. Edwin Seegmiller

Enzyme Defect Associated with a Sex-Linked Human Neurological Disorder and Excessive Purine Synthesis

A sex-linked familial neurological disease consisting of cerebral palsy, mental retardation, choreoathetosis, and compulsive aggressive behavior is associated with a loss of an enzyme that participates in purine metabolism, namely, hypoxanthine-guanine phosphoribosyltransferase. The production of excessive uric acid in this disorder implies that the enzyme is involved in the normal regulation of purine biosynthesis. This is the first example of a relation between a specific enzyme defect and abnormal compulsive behavior. It is also the first enzyme defect in purine metabolism demonstrated in a neurological disease.

The Effectiveness of the Xanthine Oxidase Inhibitor Allopurinol in the Treatment of Gout

Excerpt The clinical benefits derived from controlling the hyperuricemia of patients with gouty arthritis have been well-established (1, 2). This has been achieved by using uricosuric drugs to incr...

Urine uric acid to creatinine ratio—a screening test for inberited disorders of purine metabolism

The ratio of uric acid to creatinine (UA/C) in morning samples of urine provides a screening test for detection of the syndrome of choreoathetosis, mental retardation, self-mutilation, and hyperuricemia (Lesch-Nyhan syndrome) which is associated with virtually complete absence of activity of the enzyme phosphoribosyltransferase (PRT). This same ratio can be used on 24 hour urine samples from adult patients with gout for detection of patients with partial deficiency of the same enzyme. Data concerning UA/C from over 1,500 subjects are presented. Normal mean UA/C is 1.55 in the first week of life and declines to 0.61 at age 10. Mean for adults on normal diets is 0.49. Thirteen children with Lesch-Nyhan syndrome had a mean UA/C of 3.19, and 8 patients with gout and partial deficiency of PRT had mean UA/C of 1.06. Correlations of the ratio with age, sex, diet, and time of day, and values of UA/C in patients with gout and other disorders of purine metabolism are presented and discussed.

Adenine phosphoribosyltransferase deficiency: a previously undescribed genetic defect in man

A deficiency of adenine phosphoribosyltransferase (A-PRTase) is described in four members in three generations of one family. A-PRTase is coded by an autosome and the mutants described in this report are heterozygotes for this enzyme defect. The level of enzyme activity in these heterozygotes was inappropriately low, ranging from 21 to 37% of normal rather than the expected 50% of normal. Examination of various physical and chemical properties of the A-PRTase obtained from the mutant heterozygotes failed to reveal differences from the normal enzyme. These patients have no discernable abnormality in uric acid production despite the finding that patients with a deficiency of a closely related enzyme, hypoxanthine-guanine phosphoribosyltransferase, invariably produce excessive quantities of uric acid. A relationship of the A-PRTase deficiency to the disturbance in lipoprotein metabolism observed in the propositus has not been firmly established. Possible manifestations of the homozygous form of this enzyme deficiency will require identification of such individuals in the future.

Increased free-cystine content of fibroblasts cultured from patients with cystinosis

The presence of a significantly increased content of free-cystine in skin fibroblasts from both homozygotes and heterozygotes for cystinosis emphasizes the central role of cystine in this disease, even though the primary defect responsible for cystine accumulation is yet to be determined. The studies described in this communication provide evidence that cystine is compartmentalized in a subcellular location in cystinotic cells. In fact, the very growth of cystinotic fibroblasts in the presence more than 100 times the usual content of free-cystine is evidence that the accumulated cystine is not freely dispersed throughout the cell, since would otherwise inhibit many enzymes requiring free sulfhydryl groups for activity (Patrick, 1965). We have no evidence as to whether the cystine is located in a known subcellular organelle or in a previously unrecognized location. Skin fibroblasts may provide a convenient tool to pursue these questions.

Purine Overproduction in Man Associated with Increased Phosphoribosylpyrophosphate Synthetase Activity

In hemolyzates from red cells of two brothers with purine overproduction and gout, activity of phosphoribosylpyrophosphate synthetase is more than twofold greater than that measured in normal or other gouty individuals. The increased enzyme activity, which is also demonstrable in fibroblasts of the one patient tested, is associated with increased production of 5-phosphoribosyl-1-pyrophosphate by intact cells, an indication that the enzyme abnormality is the basis for the purine overproduction. This genetic abnormality is an example of an increased enzyme activity producing a disease state.

An enzymatic basis for variation in response to allopurinol. Hypoxanthine-guanine phosphoribosyltransferase deficiency.

Abstract Although allopurinol appears to decrease the rate of de novo purine biosynthesis, this effect is variable in gout, possibly because uric acid production is increased in patients who are relatively deficient in hypoxanthine-guanine phosphoribosyltransferase (HG-PRTase). To test this possibility, allopurinol was given to 11 patients with excessive uric acid production. In seven allopurinol had no effect on total excretion of purine catabolites. The same seven had a marked decrease in the activity of HG-PRTase and were also resistant to the effects of allopurinol on purine synthesis. These observations suggest that HG-PRTase activity is necessary for allopurinol to suppress purine synthesis de novo in man. This effect of allopurinol was also absent in four additional gouty patients with normal uric acid production and normal HG-PRTase activity. Hence, deficiency of this enzyme does not account for all cases of resistance to suppression of de novo purine biosynthesis by allopurinol.

Purine nucleotide synthesis in lymphoblasts cultured from normal subjects and a patient with Lesch-Nyhan syndrome

Human lymphoblasts derived from normal and hypoxanthine-guanine phosphoribosyltransferase (HGPRT) deficient individuals have been maintained in permanent tissue culture, and comparative studies of their purine metabolism have been undertaken. In agreement with previous observations in fibroblasts, the HGPRT-deficient lymphoblasts (less than 2% normal HGPRT activity) demonstrate threefold increases in the production of purines by the de novo pathway and four- to eightfold increases in intracellular concentrations of 5-phosphoribosyl 1-pyrophosphate (PRPP). The activities of the enzymes of purine metabolism responsible for production and utilization of PRPP were measured under optimal conditions in each cell line. The activities of adenine phosphoribosyltransferase (APRT), PRPP synthetase, and PRPP amidotransferase were independent of cell density and were not significantly different in the two cell lines. The Km values of the common substrate, PRPP, were determined in normal lymphoblast extracts for APRT (Km of 0.033 mM), HGPRT (Km of 0.074 mM), and PRPP amidotransferase (Km of 0.3 m M). The relatively low affinity of PRPP amidotransferase for PRPP suggests that deficiency of the HGPRT enzyme with its attendant increase in PRPP concentration should be accompanied by increased in vivo activity of PRPP amidotransferase, the first and presumed rate-limiting enzyme of de novo purine biosynthesis.

Relationships between glycogen storage disease and tophaceous gout

Abstract Two patients with glucose-6-phosphatase deficiency glycogen storage disease and tophaceous gout have been studied in an effort to establish the possible relationships between the primary defect in carbohydrate metabolism and their hyperuricemia and gouty arthritis. The present studies support the view that lacticacidemia is a contributing factor to the hyperuricemia of these patients. However, hypoglycemia and ketonemia probably also contribute to the urate retention. The finding of an increased rate of urate biosynthesis in the one patient whose de novo purine biosynthesis was greater than normal points to an additional mechanism for the hyperuricemia found in this type of glycogen storage disease.

Effects of orotic acid on purine and lipoprotein metabolism in man

Abstract In the present study, it was demonstrated that orotic acid, a normal intermediate in pyrimidine synthesis, inhibits purine biosynthesis de novo in normal man. This was associated with depletion of erythrocyte 5-phosphoribosyl-1-pyrophosphate (PP-ribose-P) content. Orotic acid had no inhibitory effect on purine biosynthesis in patients who exhibited elevated levels of PP-ribose-P due to a deficiency of hypoxanthine-guanine phosphoribosyltransferase. These findings suggest that the inhibitory effect of orotic acid on purine biosynthesis de novo is due to depletion of intracellular PP-ribose-P levels. This provides the first in vivo evidence that the physiologic intracellular concentration of PP-ribose-P is important for the regulation of purine biosynthesis de novo in man. Orotic acid administration also produced a modest though statistically significant decrease in the plasma concentration of cholesterol, triglycerides, and beta and prebeta lipoproteins. The uricosuric effect of orotic acid noted previously after its intravenous administration was confirmed in the present study in which the compound was administered orally.