The spectrum of hypoxanthine-guanine phosphoribosyltransferase (HPRT) deficiency. Clinical experience based on 22 patients from 18 Spanish families.

The enzyme hypoxanthine-guanine phosphoribosyltransferase (HPRT) catalyzes the reutilization of hypoxanthine and guanine to the purine nucleotides IMP and GMP, respectively. HPRT deficiency is an X-linked disorder characterized by uric acid overproduction and variable neurologic impairment. The complete deficiency of HPRT is diagnostic of Lesch-Nyhan syndrome manifested by choreoathetosis, spasticity, mental retardation, and self-injurious behavior. In some HPRT-deficient patients the enzyme defect appeared to be "partial" and the neurologic symptoms mild to severe (Kelley-Seegmiller syndrome). This has prompted the classification of HPRT deficiency in 2 distinct groups: Lesch-Nyhan syndrome and Kelley-Seegmiller syndrome, which has created much confusion. A spectrum of clinical consequences of HPRT deficiency has been recognized in small series of patients, but the complete spectrum of the neurologic disorder has not been described in a single series of patients examined by the same observers. We analyzed our experience with 22 patients belonging to 18 different families with HPRT deficiency diagnosed at "La Paz" University Hospital in Madrid over the past 16 years. The clinical spectrum of these HPRT-deficient Spanish patients was similar to the different phenotypes occasionally reported in the literature, in some cases diagnosed as Lesch-Nyhan "variants." The clinical, biochemical, enzymatic, and molecular genetic studies on these 22 patients allowed us to delineate a new classification of HPRT deficiency. Based on the neurologic symptoms, dependency for personal care, HPRT activity in hemolysate and in intact erythrocytes, and predicted protein size, patients were classified into 4 groups: Group 1 (2 patients), normal development with no neurologic symptoms, HPRT activity was detectable in hemolysates and in intact erythrocytes, and the mutation did not affect the predicted protein size. Group 2 (3 patients) mild neurologic symptoms that did not prevent independent lives, HPRT activity was detectable in intact erythrocytes, and the protein size was normal. Group 3 (2 patients), severe neurologic impairment that precluded an independent life, no residual HPRT activity, and normal protein size. Group 4 (15 patients), clinical characteristics of Lesch-Nyhan syndrome (some may not show self-injurious behavior), no residual HPRT activity, and in most (7 of 8 patients in whom the mutation could be detected) the mutation affected the predicted protein size. This classification of HPRT deficiency into 4 groups may be more useful in terms of accuracy, reproducibility, assessment for treatment trials and prognosis. The study of this Spanish series allows us to conclude that HPRT deficiency may be manifested by a wide spectrum of neurologic symptoms; the overall severity of the disease is associated with mutations permitting some degree of residual enzyme activity; and mutation analysis provides a valuable tool for prognosis, carrier identification, and prenatal diagnosis.

Renal excretion of hypoxanthine and xanthine in primary gout.

PURPOSE: The renal excretion of uric acid is usually diminished in primary gout with respect to increased serum urate levels. To determine whether the renal excretion of uric acid precursors, hypoxanthine and xanthine, is also abnormal in primary gout, the concentrations of these purines were measured in plasma and 24-hour urine samples in normal subjects, in patients with primary gout and uric acid underexcretion, and in patients with enzyme deficiencies that are known to result in over-production of uric acid. SUBJECTS AND METHODS: Three groups of subjects were studied: Group I consisted of 10 ambulatory healthy normal men; Group II consisted of 15 patients in whom primary gout was diagnosed; and Group III consisted of 10 patients with various enzyme defects known to produce an excessive synthesis of uric acid. In each subject, plasma and 24-hour urinary uric acid, hypoxanthine, xanthine, and creatinine concentrations were measured and the mean of three consecutive determinations was used. The fractional excretion of purine compounds was calculated from a formula. Hypoxanthine phosphoribosyltransferase, adenine phosphoribosyltransferase, and hemoglobin were also measured in each subject. RESULTS: Plasma hypoxanthine and xanthine were increased in the two groups of patients compared with the control subjects. Urinary hypoxanthine and xanthine levels were reduced in gouty patients compared with control subjects, whereas levels were increased in patients with uric acid overproduction. A positive correlation was found between the renal clearances of uric acid, hypoxanthine, and xanthine. CONCLUSION: The results indicate that the renal excretion of hypoxanthine and xanthine is severely impaired in most patients with primary gout.

Albumin excretion rate and metabolic modifications in patients with essential hypertension. Effects of two angiotensin converting enzyme inhibitors.

A prospective randomized, double-blind, double-dummy study investigated the effects of two angiotensin converting enzyme (ACE) inhibitors on urinary albumin excretion in nondiabetic patients with mild to moderate essential hypertension. At the end of a 4-week placebo run-in period, 36 patients were randomly allocated to receive a 12-week course of treatment with quinapril (10, 20, or 40 mg) once daily or captopril (25, 50, or 75 mg) twice daily. Seventeen patients in each group completed the study. The mean change in mean blood pressure for patients taking quinapril (mean dose 32 mg/24 h) was -5 mm Hg (P = .002), and for patients taking captopril (mean dose 132 mg/24 h), -9 mm Hg (P = .002). The baseline urinary albumin excretion rate in both groups was (mean +/- EEM) 57 +/- 7 micrograms/min. Fifteen patients in the quinapril group and 12 patients in the captopril group had baseline albumin excretion rates of more than 20 micrograms/min. Mean urinary albumin excretion decreased in patients treated with quinapril from 55 to 33 micrograms/min (mean decrease 22 micrograms/min, 95% confidence interval [CI], 1 to 43 micrograms/min; P = .031) and with captopril from 59 to 41 micrograms/min (mean decrease 18 micrograms/min, 95% CI, 3 to 32 micrograms/min; P = .025). No significant modifications were observed in serum lipid concentrations, serum and urinary electrolytes, and magnesium or phosphorus metabolism. Mean urinary calcium excretion decreased in the quinapril-treated group (from 219 to 188 mg/24 h; P = .023) but not in the captopril group (from 264 to 267 mg/24 h).(ABSTRACT TRUNCATED AT 250 WORDS)

Plasma oxypurinol concentration in a patient with allopurinol hypersensitivity.

Monitoring of plasma oxypurinol has been proposed to prevent allopurinol side effects. An 89-year-old man developed a severe desquamative rash, fever, eosinophilia, hepatocellular injury and renal failure after allopurinol administration. Eight hours after the last dose, plasma allopurinol was undetectable and plasma oxypurinol was 50 mumol/l. This is the first case in which severe allopurinol hypersensitivity occurred despite a simultaneous plasma oxypurinol concentration within recommended levels (below 100 mumol/l).