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Background: Although glucose-6-phosphate isomerase (G6PI), anti-G6PI antibodies and G6PI-containing immune complexes (G6PI-CIC) have proved high expression in patients with rheumatoid arthritis (RA), comprehensive evaluation of the G6PI-derived markers, G6PI antigen, anti-G6PI Abs, G6PI-CIC and G6PI mRNA, in the diagnosis of RA remains necessary., Methods: We measured G6PI antigen, anti-G6PI Abs, C1q/G6PI-CIC as well as anti-cyclic citrullinated peptide antibodies (anti-CCP Abs) in serum and concomitantly synovial fluid (SF) by ELISA in RA, other rheumatic diseases and healthy controls. The G6PI mRNA expression in peripheral blood mononuclear cells (PBMCs) was assessed with real-time PCR., Results: As compared with non-RA patients, RA patients had increased levels of G6PI antigen, anti-G6PI Abs, C1q/G6PI-CIC and G6PI mRNA expression in sera or PBMCs, and increased levels of G6PI and C1q/G6PI-CIC in SF. The serum G6PI levels in RA patients positively correlated with anti-G6PI Abs, C1q/G6PI-CIC, G6PI mRNA, anti-CCP Abs, RF, CRP and ESR, respectively. The area under curve analyses demonstrated that serum G6PI had the best discriminating power for RA and active RA followed by C1q/G6PI-CIC, anti-G6PI Abs and G6PI mRNA. The simultaneous use of serum G6PI and anti-CCP Abs assays in the form of either of them tested positive gave improved sensitivities of 88.1% for RA and 95.8% for active RA., Conclusions: Despite the elevated expression of all G6PI-derived markers in RA, the serum G6PI has the best discriminating power among the four G6PI-derived markers. The serum G6PI determination either alone or in combination with anti-CCP Abs improves the diagnosis of RA., (Copyright © 2010 Elsevier B.V. All rights reserved.)

A new case of glucosephosphate isomerase deficiency in a Belgian family is described. The activity of the enzyme was decreased to about 25-30% of the normal value. Characterization of the defect enzyme showed a decreased thermostability. Heating of the enzyme at 45 degrees C showed a loss of activity of 50% after 90 min. The pH-optimum and the KM-value for fructose 6-phosphate were normal. The electrophoretic pattern showed a faster migration. The variant described here differs from all known variants. Therefore we propose to give to this new variant the name GPI-Kortrijk.

Acquired enzymatic activity defects of erythrocyte pyruvate kinase, glucose phosphate isomerase and phosphofructokinase have been studied in patients with acute myeloid leukemias, sideroblastic refractory anemias and unclassified acquired dyserythropoiesis. 6 patients with acute myeloid leukemia had a lowered erythrocyte pyruvate kinase activity; in 5 of them the concentration of the "pyruvate kinase"-antigen was parallely decreased, in such a manner that the ratio enzyme activity/immunologic reactivity (i.e. the molecular specific activity) was normal. In 1 patient with acute leukemia, 4 with refractory anemia and 1 with acquired dyserythropoiesis the defect of the pyruvate kinase activity was associated with a normal antigen concentration (and, therefore, the molecular specific activity in whole hemolysate was lowered). The enzyme activity was restored by incubation with SH reagents in two cases and by partial purification as often as it was performed. The electrofocusing pattern of erythrocyte pyruvate kinase was normal in both these types of defects. In two patients with so-called "acquired dyserythropoiesis" an erythrocyte glucose phosphate isomerase deficiency has been detected; in both the cases it was associated with a parallel decrease of the antigen concentration. The residual enzyme had a normal electrofocusing and electrophoretic pattern and a normal heat stability; the enzyme activity could not be restored by any treatment. In 1 patient with erythroleukemia and in 1 other with acquired dyserythropoiesis the erythrocyte phosphofructokinase activity was lowered. The enzyme activity was not restored by cross incubation in isologous plasma or by the SH reagents. In one case immunologic study could be performed, indicating that the enzyme defect was mainly due to the decreased ratio of the muscle type subunit of the erythrocyte phosphofructokinase. The electrofocusing pattern of deficient phosphofructokinases was normal. Finally, we point out the probable existence of several direct mechanisms, genetic and post translational, accounting for the acquired enzyme defects of red blood cells in various blood disorders.

Serum creatine kinase (CK) and lactate dehydrogenase (LD) isoenzymes were determined electrophoretically, along with various other biochemical markers of malignancy, in 19 patients with metastatic carcinoma of the prostate. Mitochondrial CK appeared in 15 patients, the CK-BB isoenzyme in 6. As a result, CK activity not inhibited by anti-M-subunit antibodies, CK non-M, was above the reference value in altogether 17 patients. There was a cathodic shift among the LD isoenzymes, significantly more prominent with increasing total LD, and a positive correlation between elevations of CK non-M and LD-5, suggesting a relation to tumour burden for both. An LD 'flip' (LD-1 greater than LD-2) was present in 10/15 patients. The frequency of CK non-M elevations was similar to--but not quantitatively correlated with--elevations of prostatic acid phosphatase and alkaline phosphatase. Thus, changes in CK and LD patterns are frequent in patients with prostatic cancer and must be taken into consideration when acute cardiac symptoms are evaluated in such patients.

A new genetic variant form of glucosephosphate isomerase has been found in a family heterozygous for the mutant allele. The mutant enzyme, unlike other phenotypic variants, does not appear to be the result of a single amino acid replacement. The allozyme exhibits an isoelectric point of 5.7 and is thus much more acidic than the normal enzyme (pI = 9.3). The allozyme has been isolated from placenta and separated from the normal homodimer and heterodimer by isoelectric focusing. The enzyme exhibits normal Km and Ki values for the substrates and competitive inhibitors. The allozyme exhibits a normal pH optimum and thermal stability. However, the molecular specific activity of the variant enzyme as quantitated by radioimmunoassay is significantly lower than normal. Analytical gel filtration revealed that the molecular weight of the weight of the enzyme is significantly lower than the normal enzyme. These data thus suggest that the phenotype is unlike any previously reported and is due to a deletion mutation.