[Biochemical, enzymatic and genetic study of hypoxanthine guanine phosphoribosyl transferase (HPRT) deficiency]. / Estudio bioquímico, enzimático y genético de la deficiencia de hipoxantina guanina fosforribosiltransferasa (HPRT).

OBJECTIVE: The objective of this study was to analyze the diagnosis of HPRT deficiency, perform a thorough purine metabolism study and to establish the carrier and prenatal diagnosis in 16 HPRT deficient families. PATIENTS AND METHODS: Plasma and urinary concentrations of uric acid, creatinine and oxypurines, APRT and HPRT activities in hemolysates and HPRT in intact erythrocytes and adenine 8-C14 urinary excretion were analyzed. Carrier diagnosis was made by hair root enzyme analysis and genetic studies. RESULTS: These studies allowed the diagnosis of HPRT deficiency in 20 patients. Carrier diagnosis could be performed in 23 women at risk and in a 9 week old female fetus. CONCLUSIONS: The study results suggest that HPRT deficiency accounts for increased purine nucleotide degradation. This increase results in elevated urinary and plasma concentrations of hypoxanthine, xanthine and uric acid. The clinical severity of the disease is not related to the degree of urinary or plasma concentrations of oxypurines. Hair root analysis generally allows the diagnosis of carrier status, but the carrier state cannot be fully excluded in women at risk. When the familial mutation causing the defect in HPRT is known, analysis of the differences in the restriction pattern of the HPRT gene (natural or due to directed mutagenesis) allow a rapid and reliable diagnosis of carrier status and HPRT deficiency.

[Evaluation of microalbuminuria in children]. / Valoración de microalbuminuria en una población pediátrica.

Microalbuminuria has been shown to be important for the diagnosis and prognosis of glomerular nephropathy. A few studies in normal healthy children were performed. The concentration of albumin was determined in 171 samples of the first morning urine by an immunoturbidimetric method. Microalbumin/creatinine ratio values were 4.07 +/- 0.11 mg/mmol, 1.16 +/- 0.10 mg/mmol and 0.88 +/- 0.11 mg/mmol in children of ages 4 days-1 year, 1-7 years and 7-15 years, respectively. We found a negative inverse correlation (r = 0.31; p < 0.05) between age and microalbumin/creatinine ratio.

[Prenatal diagnosis of Lesch-Nyhan syndrome]. / Diagnóstico prenatal del síndrome de Lesch-Nyhan.

A pregnant woman with Lesch-Nyhan's syndrome (hypoxanthine-guanine-phosphoribosyltransferase, or HGPRT deficiency) requested antenatal diagnosis. HGPRT and adenine phosphoribosyltransferase (APRT) activities were measured in fetal erythrocytes by funiculocentesis in the 21st gestational week. HGPRT activity was lower than 0.01 mmol/h/Hb g (normal value 87.0 +/- 16.05 mmol/h/Hb g). APRT activity was increased (44.0 mmol/h/Hb g) as compared with that from 50 normal individuals (28.1 +/- 6.9 mmol/h/Hb g). Pregnancy was interrupted and the antenatal diagnosis of Lesch-Nyhan's syndrome was confirmed after delivery. In the 20th gestational week, amniotic fluid showed a marked increase if oxypurines (hypoxanthine, xanthine and uric acid) as compared with the values in 14 amniotic fluids from normal pregnancies and gestational age within 15-22 weeks. The present study illustrates the possibility to make the antenatal diagnosis of Lesch-Nyhan's syndrome by funiculocentesis . The previously unreported finding of a marked abnormality of oxypurine concentration in amniotic fluid represents a new outlook for the diagnosis of enzymatic defects of synthesis and degradation of purine nucleotides.

[Metabolism of purine nucleotides in the central nervous system in patients with phosphoribosylpyrophosphate synthetase hyperactivity and neurosensory deafness]. / Metabolismo de nucleótidos purínicos en el sistema nervioso central de pacientes con sobreactividad de fosforribosilpirofosfato (PRPP) sintetasa y sordera neurosensorial.

The overactivity of PRPP synthetase is transmitted as a sex-linked abnormality, being characterized by uric acid overproduction and, in some patients, by muscular hypotonia, neurosensitive deafness and/or ataxia. The pathogenesis of these neurologic abnormalities is not yet known. The CSF concentrations of end products of the neuronal metabolism of purines--hypoxanthine for the adenine nucleotides and xanthine for guanine nucleotides--have not been previously studied in patients with overactivity of PRPP synthetase. We have evaluated the plasma and CSF levels of hypoxanthine and xanthine in a 8-year-old male with tophaceous gout and neurosensitive deafness and in his mother, who had gout without neurological involvement. PRPP synthetase overactivity was demonstrated in fibroblast culture; the male was hemizygote and his mother was heterozygotic. In 4 normal individuals, the plasma levels of hypoxanthine and xanthine were 1.7 +/- 0.4 microM and 0.9 +/- 0.2 microM (mean +/- SEM), respectively, while in in CSF they were 3.3 +/- 1.1 microM and 2.0 +/- 0.2 microM. The hemizygote male showed a considerable increase in hypoxanthine level (5.6 microM in plasma and 22.1 microM in CSF); the plasma and CSF xanthine levels were 1.8 and 4.5 microM, respectively. The heterozygotic female showed moderately increased plasma hypoxanthine levels (3.9 and 10.6 microM) and normal xanthine levels (1.3 and 1.8 microM). These results suggest an increase in the degradation of purine nucleotides in the central nervous system of patients with PRPP synthetase overactivity and neurological symptoms. The predominance of hypoxanthine over xanthine may indicate a greater increase of the degradation of adenine rather than guanine nucleotides.

[Plasma hypoxanthine and intraerythrocytic ATP in umbilical cord blood as markers of perinatal hypoxia]. / La hipoxantina plasmática y el ATP intraeritrocitario en sangre de cordón umbilical como marcadores de hipoxia perinatal.

We determined blood pH, plasma hypoxanthine (Hx) and intraerythrocyte ATP (iATP) concentrations in umbilical cord blood from 20 normal newborn infants (10 delivered by the vaginal route and 10 by caesarean section) and in 18 newborns with clinical signs of perinatal asphyxia (9 with meconium stained amniotic fluid and 9 with fetal bradycardia). Blood pH was significantly lower in infants with clinical signs of perinatal asphyxia (p less than 0.01). Four newborns with meconium or bradycardia had pH values within normal control levels. Hx concentrations were lower in infants delivered by caesarean section with respect to normal infants born by the vaginal route (p less than 0.05). Newborns with meconium or fetal bradycardia showed Hx concentrations higher than normal newborns (p less than 0.01), but 2 infants with signs of perinatal hypoxia had Hx levels within the normal newborn range. All babies with meconium or bradycardia had an iATP concentration lower than control infants (p less than 0.01). These results indicate that: the pH and Hx determinations in the newborn may underestimate hypoxia and, that measurement of iATP may be useful parameters to asses perinatal hypoxia.

[Degradation of purine nucleotides in patients with chronic obstruction to airflow]. / Degradación de los nucleótidos purínicos en pacientes con obstrucción crónica al flujo aéreo.

The increase in hypoxanthine (Hx), xanthine (X), uric acid (VA) and total purines (TP) that may be found in several clinical conditions associated with tissue hypoxia has been attributed to an increase in adenine nucleotides degradation by a reduced ATP synthesis caused by oxygen deprivation. To test this hypothesis we have investigated the urinary excretion of Hx, X, VA, TP and radioactivity elimination after labeling the adenine nucleotides with adenine (8-14C) in 5 patients with chronic airflow obstruction (CAFO), in the basal state and after oxygen therapy (FiO2, 24%). The results were compared with those from 4 normal individuals. Patients with COFA showed an increase of the renal elimination of Hx, X, VA, TP and radioactivity, which was significantly different from the control group (p less than 0.05). Oxygen administration was associated with a significant reduction in the excretion of purines and radioactivity (p less than 0.01), which decreased to values similar to those found in normal individuals. These findings suggest that in patients with COFA and severe hypoxemia there is a marked increase in the degradation of adenine nucleotides. The normalization of the purine and radioactivity excretion after oxygen therapy points to a basic role of oxygen in the catabolism of adenine nucleotides.

[Purine transport through the blood-brain barrier in hypoxanthine phosphoribosyltransferase deficiency]. / Transporte de purinas a través de la barrera hematoencefálica en la deficiencia de hipoxantina fosforribosiltransferasa.

The transfer of purines through the hematoencephalic barrier is poorly understood. Allopurinol inhibits the enzyme xanthine oxidase and increases xanthine and hypoxanthine plasma levels, but it should not increase the cerebrospinal fluid (CSF) levels of these purines owing to the absence of xanthine oxidase in the central nervous system (CNS). In the present study we evaluated the plasma and CSF concentrations of uric acid, hypoxanthine, xanthine and inosine in the baseline state and after 7 days of allopurinol administration (5-10 mg/kg/24 h) in 4 patients with hypoxanthine phosphoribosyltransferase (HPRT) deficiency. The CSF uric acid level was positively correlated with its plasma level (r = 0.93, p less than 0.01). The CSF hypoxanthine and xanthine concentrations were, as a mean, 5 and 2 times higher, respectively, in patients with HPRT deficiency than in 4 control individuals. As hypoxanthine basically comes from adenine nucleotides, while xanthine comes from guanine nucleotides, this finding suggests that in the CNS of patients with HPRT deficiency there is a higher degradation level of adenine nucleotides than of guanine nucleotides. Allopurinol increased plasma concentration of hypoxanthine, xanthine and inosine 4, 10 and 3 times, respectively, in relation to baseline values. In CSF, the mean increase of hypoxanthine and xanthine concentration was 17.5 mumol and 7.7 mumol, respectively, whereas inosine level was unchanged. These results suggest that in HPRT deficiency hypoxanthine and xanthine may be transferred to the brain.