Contributions
Type: Publication Only
Background
Glucose-6-phosphate isomerase (GPI, EC 5.3.1.9) is a dimeric enzyme that catalyses the reversible isomerisation of glucose-6-phosphate (G6P) to fructose-6-phosphate (F6P), the second reaction step of glycolysis. GPI deficiency, transmitted as an autosomal recessive trait, is the second most common erythro-enzymopathy of anaerobic glycolysis, after pyruvate kinase. GPI deficient patients are affected by chronic non-spherocytic hemolytic anemia of variable severity; in rare cases mental retardation 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 60 cases of GPI deficiency have been described, and 35 mutations have been reported at the nucleotide level.
Aims
We report the clinical, haematological and molecular characteristics of 10 GPI deficient cases
Methods
10 patients (6 males, 4 females) from 9 families, with a median age at admission of 7 yrs (range 1-51) were studied. Eight patients were of Italian origin and 2 were Turkish. Haematological parameters and red cell enzyme activity were determined according to standard methods. The entire coding region of the GPI gene was amplified by PCR and automatically sequenced.
Results
Main clinical and haematologic parameters and results of the molecular characterization are reported in Table 1. All patient displayed anaemia at birth or in the early infancy; neonatal jaundice was observed in 4 patients, 3 of whom required exchange transfusion. All patients needed blood transfusion in childhood: 3 regularly (every 4-8 weeks), the remaining occasionally in concomitance of haemolytic crises due to infections. Splenectomy, performed in 5 patients, did not lead to normalization of anaemia, only resulting in a slightly increase of Hb levels (0.5-1 g/dL) but it eliminated transfusion requirement; bilirubin levels increased after splenectomy in 3 cases. No patient needed transfusions in adulthood; however, two underwent chelation therapy for iron overload. None showed neurological signs.
Eleven different mutations were found in GPI gene, 4 of them never described before (c.311 G>A, c.307C>G, c.269T>C, c.1066G>A); all the new mutations affect highly conserved residues, were not detected in Ensembl and 1000 genomes database, and were predicted to have pathogenic effects by Polyphen, SIFT analysis. In particular, mutation Asp356Asn falls in a region involved in the sugar isomerase domain and dimer-dimer interface, and it is part of active site, further suggesting its drastic effect. In one patient we were unable to find the second mutation; however, the loss of heterozygosity at the cDNA level suggested the presence of a null mutation of the paternal GPI allele
Summary
We characterized the largest series of GPI deficient patients so far reported. Patients present with moderate/severe anaemia that improve with aging. The study confirms the great heterogeneity of the molecular defect. Although neurological impairment is sometime reported in literature in GPI deficiency, none of the cases here described displayed extra-haematological symptoms.
Keyword(s): Hemolytic anemia, Mutation analysis, Red blood cell
Type: Publication Only
Background
Glucose-6-phosphate isomerase (GPI, EC 5.3.1.9) is a dimeric enzyme that catalyses the reversible isomerisation of glucose-6-phosphate (G6P) to fructose-6-phosphate (F6P), the second reaction step of glycolysis. GPI deficiency, transmitted as an autosomal recessive trait, is the second most common erythro-enzymopathy of anaerobic glycolysis, after pyruvate kinase. GPI deficient patients are affected by chronic non-spherocytic hemolytic anemia of variable severity; in rare cases mental retardation 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 60 cases of GPI deficiency have been described, and 35 mutations have been reported at the nucleotide level.
Aims
We report the clinical, haematological and molecular characteristics of 10 GPI deficient cases
Methods
10 patients (6 males, 4 females) from 9 families, with a median age at admission of 7 yrs (range 1-51) were studied. Eight patients were of Italian origin and 2 were Turkish. Haematological parameters and red cell enzyme activity were determined according to standard methods. The entire coding region of the GPI gene was amplified by PCR and automatically sequenced.
Results
Main clinical and haematologic parameters and results of the molecular characterization are reported in Table 1. All patient displayed anaemia at birth or in the early infancy; neonatal jaundice was observed in 4 patients, 3 of whom required exchange transfusion. All patients needed blood transfusion in childhood: 3 regularly (every 4-8 weeks), the remaining occasionally in concomitance of haemolytic crises due to infections. Splenectomy, performed in 5 patients, did not lead to normalization of anaemia, only resulting in a slightly increase of Hb levels (0.5-1 g/dL) but it eliminated transfusion requirement; bilirubin levels increased after splenectomy in 3 cases. No patient needed transfusions in adulthood; however, two underwent chelation therapy for iron overload. None showed neurological signs.
Eleven different mutations were found in GPI gene, 4 of them never described before (c.311 G>A, c.307C>G, c.269T>C, c.1066G>A); all the new mutations affect highly conserved residues, were not detected in Ensembl and 1000 genomes database, and were predicted to have pathogenic effects by Polyphen, SIFT analysis. In particular, mutation Asp356Asn falls in a region involved in the sugar isomerase domain and dimer-dimer interface, and it is part of active site, further suggesting its drastic effect. In one patient we were unable to find the second mutation; however, the loss of heterozygosity at the cDNA level suggested the presence of a null mutation of the paternal GPI allele
Summary
We characterized the largest series of GPI deficient patients so far reported. Patients present with moderate/severe anaemia that improve with aging. The study confirms the great heterogeneity of the molecular defect. Although neurological impairment is sometime reported in literature in GPI deficiency, none of the cases here described displayed extra-haematological symptoms.
Keyword(s): Hemolytic anemia, Mutation analysis, Red blood cell