The diagnostic value of thrombocytic glucose-6-phosphatase in patients with von Gierke's disease and its heterozygotes

Determination of human plasma xanthine oxidase activity by high-performance liquid chromatography

An assay for human plasma xanthine oxidase activity was developed with pterin as the substrate and the separation of product (isoxanthopterin) by high-performance liquid chromatography with a fluorescence detector. The reaction mixture consists of 60 microliters of plasma and 240 microliters of 0.2 M Tris-HCl buffer (pH 9.0) containing 113 microM pterin. With this assay, the activity of plasma xanthine oxidase could be easily determined despite its low activity. As a result, it could be demonstrated that the intravenous administration of heparin or the oral administration of ethanol did not increase plasma xanthine oxidase activity in normal subjects, and also that plasma xanthine oxidase activity was higher in patients with hepatitis C virus infection than in healthy subjects or patients with gout. In addition, a single patient with von Gierke's disease showed a marked increase in the plasma activity of this enzyme, relative to that apparent in normal subjects.

Unreliability of platelet glucose-6-phosphatase for the diagnosis of glycogen storage disease type Ia

The diagnosis of glycogen storage disease type Ia currently uses enzyme analysis of liver tissue. This requires liver biopsy in the at-risk neonate or fetus. Conflicting reports have appeared in the literature on the use of peripheral platelet glucose-6-phosphatase activity for the diagnosis of this disorder. We have applied a sensitive radiometric assay system to the measurement of glucose-6-phosphatase activity in peripheral platelets. Two families with affected members were analysed, revealing no differences in glucose-6-phosphatase activity as compared with control values. Platelet measurement of glucose-6-phosphatase does not appear to be useful for the diagnosis of glycogen storage disease type Ia.

Clinical and enzymological studies in a child with type I glycogen storage disease associated with partial deficiency of hepatic glucose-6-phosphatase

1. GSD-I is described in a child with partial deficiency of hepatic glucose-6-phosphatase. 2. Growth retardation and hepatosplenomegaly were major clinical features. 3. Hyperlipidaemia, lactic acidaemia, hyperuricaemia and reduced uric acid clearance were major biochemical findings. 4. Although the glucose response to glucagon and galactose was impaired, there was a striking absence of hypoglycaemia which may be attributable to residual catalytic activity of the enzyme. 5. Preliminary studies of the crude liver enzyme showed it to have a normal pH inactivation profile and apparent Km with a reduced Vmax. 6. No evidence of increased PP-ribose-P availability in fresh liver tissue was detected. 7. Continuous glucose feeding resulted in accelerated growth without complete correction of lactic acidosis or hyperuricaemia. 8. GSD-I with partial deficiency of hepatic glucose-6-phosphatase should be considered in patients with gout or hyperuricaemia associated with hypertriglyceridaemia and lactic acidaemia even in the absence of hypoglycaemia.

Glucose-6-phosphatase activity in liver and blood platelets of two patients with glycogen storage disease type I

Glucose-6-phosphatase (G-6-Pase) activity in liver and blood platelets of two patients with glycogen storage disease (GSD) type I is described. Both patients had a reduced activity of G-6-Pase in liver. The km value for glucose 6-phosphate (G-6-P) of residual activity in liver of both patients was similar to that of control liver. We could not demonstrate any reduced activity of platelet G-6-Pase in the patients. Platelet G-6-Pase with our assay method seems to represent a nonspecific phosphatase activity. Our observation suggests that it is necessary to examine platelet G-6-Pase of many other patients with GSD type I to confirm that G-6-Pase deficiency can be diagnosed by enzyme assay performed on blood platelets.

Reassessment of elevated serotonin levels in blood platelets in early infantile autism

Blood platelet serotonin content was measured in 30 children with early infantile autism, as defined by Kanner, 30 age-matched normal subjects, and 45 children with various neurological and psychiatric disorders. Serotonin content in the autistic group was 980 +/- 357 ng/mg platelet protein (mean +/- standard deviation), a value significantly higher than that for normal children, 807 +/- 202 ng/mg (p less than .025). Autistic children under school age had higher platelet serotonin concentrations than other older autistic individuals. There was little correlation between age and serotonin levels in the normal children. Elevated serotonin was also seen in some of the non-autistic pathological group, who were disturbed and hyperactive. Elevated serotonin levels are not necessarily a specific biochemical finding for autistic children, but seem to be due to their behavioral distinction.

Reduction of blood platelet serotonin levels in manic and depressed patients

Blood platelet serotonin levels were measured in unmedicated 12 manic and 74 depressive patients with 118 normal control subjects employed. Blood platelets were separated by multiple centrifugation in the medium of Na2-EDTA solution, and the loss of serotonin during collecting procedures was about 11%. The mean value of blood platelet serotonin levels in depressed patients was 594 +/- 288 ng/mg platelet protein (+/- S.D.), which was significantly lower than that for normal controls, 780 +/- 253 ng/mg protein (p less than 0.001). Age does not account for the reduction of serotonin levels both in depressed and in normal population. Unipolar and involutional depressed patients exhibited to have the most pronounced reduced levels of serotonin of various subtypes of depression, while bipolar depressed patients, neurotic and chronic characterological depressed patients as well as patients with first-episode depression had the values which were comparable with those in normal controls. Manic patients did not show enhancement but did reduction of serotonin levels, the mean being 580 +/- 152 ng/mg protein, which made a contrast with their clinical manifestations of exhilaration and hyperactivity. Changes in blood platelet serotonin levels were determined before, during and after administration of L-5-HTP with a maintenance dose of 300 mg daily in nine depressed patients. Serotonin levels in all subjects were lifted to normal levels during the L-5-HTP treatment, while clinical symptoms were not improved with the treatment. Reduction of blood platelet serotonin levels in depressed patients may be due to their psychobiological distinction, which involves abnormal biogenic amine metabolism in the brain.

Urate production in heterozygotes for glucose-6-phosphatase deficiency

Urate production and excretion were studied in heterozygous parents of a child with glucose-6-phosphatase deficiency. Both parents demonstrated glucose-6-phosphatase concentrations in platelets intermediate between those in the homozygote and the normal. The miscible urate pool and turnover rate, the rate of incorporation of [14C]glycine into urate, the renal clearance of urate and the percentage excretion of labelled urate by the renal route were within the normal range in both heterozygotes, as were the serum cholesterol and triglyceride concentrations. Thus, a partial deficiency of glucose-6-phosphatase was not associated with the abnormalities of urate or lipoprotein metabolism which are features of homozygous glucose-6-phosphatase deficiency. Erythrocyte phosphoribosyl-pyrophosphate concentration, an increased concentration of which has been postulated as the mechanism responsible for the increased de novo purine biosynthesis in glucose-6-phosphatase deficiency, was found to be within the normal range in erythrocytes from both a homozygote and a heterozygote for this condition.

Insignificance of gluconeogenesis in human blood platelets

Human blood platelets contain no detectable activity of the enzymes fructose diphosphatase (EC 3.1.3.11), phospho-enolpyruvate carboxykinase (EC 4.1.1.32) and pyruvate carboxylase (EC 6.4.1.1.). Glucose-6-phosphatase (EC 3.1.3.9) activity is very low. Phosphofructokinase present in human blood platelets, catalyzes a reaction which can be stimulated by AMP in a platelet homogenate, due to the presence of endogenous ADP and myokinase. These enzymes are responsible for the formation of fructose-6-phosphate from fructose-1, 6-diphosphate. Pyruvate kinase (EC 2.7.1.40) in human blood platelets belongs to the M-type, which is not inhibited by ATP, at least not under the conditions applied. The results obtained indicate that gluconeogenesis in human blood platelets is not present in the way which has been established for liver and kidney.