Clinical and Molecular Spectrum of Glucose-6-Phosphate Isomerase Deficiency. Report of 12 New Cases

Abstract

Glucose-6-phosphate isomerase (GPI, EC 5.3.1.9) is a dimeric enzyme that catalyzes the reversible isomerization of glucose-6-phosphate to fructose-6-phosphate, the second reaction step of glycolysis. GPI deficiency, transmitted as an autosomal recessive trait, is considered the second most common erythro-enzymopathy of anaerobic glycolysis, after pyruvate kinase deficiency. Despite this, this defect may sometimes be misdiagnosed and only about 60 cases of GPI deficiency have been reported. GPI deficient patients are affected by chronic non-spherocytic hemolytic anemia of variable severity; in rare cases, intellectual disability or neuromuscular symptoms have also been reported. The gene locus encoding GPI is located on chromosome 19q13.1 and contains 18 exons. So far, about 40 causative mutations have been identified. We report the clinical, hematological and molecular characteristics of 12 GPI deficient cases (eight males, four females) from 11 families, with a median age at admission of 13 years (ranging from 1 to 51); eight of them were of Italian origin. Patients displayed moderate to severe anemia, that improves with aging. Splenectomy does not always result in the amelioration of anemia but may be considered in transfusion-dependent patients to reduce transfusion intervals. None of the patients described here displayed neurological impairment attributable to the enzyme defect. We identified 13 different mutations in the GPI gene, six of them have never been described before; the new mutations affect highly conserved residues and were not detected in 1000 Genomes and HGMD databases and were considered pathogenic by several mutation algorithms. This is the largest series of GPI deficient patients so far reported in a single study. The study confirms the great heterogeneity of the molecular defect and provides new insights on clinical and molecular aspects of this disease.

Targeted Next Generation Sequencing and Diagnosis of Congenital Hemolytic Anemias: A Three Years Experience Monocentric Study

“…Eight cases from six families had a biochemical diagnosis of enzyme defect; two were confirmed to have pyruvate kinase (PK) deficiency, three from two families glucose-6-phosphate dehydrogenase (G6PD) deficiency and one was found to have one mutation in GPI gene, in compound heterozygosity with the polymorphism c.489A > G (p.Gly163 = rs1801015), possibly associated to splicing alterations (Fermo et al, 2019); in two related cases no mutations in PKLR gene were found in spite of a slightly decreased PK activity detected by enzymatic assay.…”

In silico study of peculiarities of metabolism of erythrocytes with glucosephosphate isomerase deficiency

“…Glucose phosphate isomerase (GPI, EC 5.3.1.9) catalyzes the isomerization reaction of a pyranose six-membered ring in glucose-6-phosphate to a furanose five-membered ring in fructose-6-phosphate. An important feature of identifying a GPI defective enzyme is the change in its physico-chemical properties (thermostability, isoelectric point, and electrophoretic motion) and its kinetic properties (Repiso et al, 2006;Warang et al, 2012;Fermo et al, 2019). Abbreviations for metabolites: ADE, adenine, ADO, adenosine, SAdoHcy, S-adenosylhomocysteine, D13PG, 1,3-biphosphoglycerate, D23PG, 2,3diphosphoglycerate, DHAP, dihydroxyacetone phosphate, ERY4P, erythrose 4-phosphate, F6P, fructose-6-phosphate, FDP, fructose diphosphate, G6P, glucose-6-phosphate, GA3P, glyceraldehydes-3-phosphate, GL6P, 6-phosphogluco lactone, GLC, glucose, GO6P 6-phosphogluconate, GSH, reduced glutathione, GSSG, oxidized glutathione, Hcy, homocysteine, H2O2, hydrogen peroxide, HYPX, hypoxanthine, IMP, inosine monophosphate, INO, inosine, LAC, lactate, P2G, 2-phosphoglycerate, P3G, 3-phosphoglycerate, PEP, phosphenolpyruvate, PRPP, 5-phosphoribosyl pyrophosphate, PYR, pyruvate, R1P, ribose-1-phosphate, R5P, ribose-5-phosphate, RL5P, ribulose-5-phosphate, SAM, S-adenosylmethionine, SED7P, sedoheptulose 7phosphate, XYL5P, xylose-5-phosphate, Gly, glycine, Gln, glutamine, Glu, glutamic acid, Cys, cysteine.…”

“…Despite glucosephosphate isomerase (GPI) deficiencies being quite rare, they are the third frequent cause of nonspherocytic hemolytic anemia (Zaidi et al, 2017;Grace & Glader, 2018;Burger et al, 2019) associated with the mutation of the GPI gene. This gene contains 18 exons and produces 1.9 kb mRNA, which encodes a 558 amino acids protein (Lin et al, 2015;Zaidi et al, 2017;Fermo et al, 2019). The molecular characterization of known GPI variants indicates that gene defects are predominantly point mutations (Jamwal et al, 2017;Burger et al, 2019;Fermo et al, 2019).…”

“…This gene contains 18 exons and produces 1.9 kb mRNA, which encodes a 558 amino acids protein (Lin et al, 2015;Zaidi et al, 2017;Fermo et al, 2019). The molecular characterization of known GPI variants indicates that gene defects are predominantly point mutations (Jamwal et al, 2017;Burger et al, 2019;Fermo et al, 2019). Low enzyme activity and its nonstability results from impaired kinetic properties, reduced thermo stability of the mutant enzyme, or defective protein folding (Kugler & Lakomek, 2000;Koralkova et al, 2014;Lin et al, 2015).…”

“…However, in many cases, the decline in the activity of the enzyme seems to be clearly not enough to disrupt the normal metabolism. In hemolytic anemia associated with enzymopathy, the activity of other key enzymes and the metabolites' content may exceed the normal level up to several times, be-cause of the high reticulocytosis (Rossi et al, 2010, Warang et al, 2012Mojzikova et al, 2018;Fermo et al, 2019). It is known that young erythrocytes, formed in conditions of intense erythropoiesis, are unstable and age rapidly, especially in the presence of unstable enzymes (Mairbäurl, 2018).…”