PF434 GLUCOPHOSPHATE ISOMERASE DEFICIENCY IDENTIFIED BY NEXT-GENERATION SEQUENCING
Authors: S.M. M. Vora, M. Proven, R. Hipkiss, P. Ware, K. Howard, H. Dreau, S. Baird, W. Ouwehand, K. Megy, K.E. Stirrups, N. BioResource, D. Lim, A. Norton, A. Kumar, I. Roberts, M. Layton, N.B. Roy
Journal: HemaSphere (2019)

Background: Glucophosphate isomerase (GPI) deficiency is a rare erythroenzymopathy causing a defect in the glycolytic pathway. Prevalence is less than 1 in a million and inheritance is autosomal recessive. The diagnosis should be considered in those presenting with acute or chronic haemolysis, with a normal blood film and negative direct antibody screen. Molecular genetic analysis can be diagnostic and is confirmed functionally with GPI enzyme assay. 69 causal variants have been described in the GPI gene and over 50 clinical cases described. Aims: To study cases of GPI deficiency identified by the Oxford Red Cell Panel (ORCP) and identify the clinical features that should alert clinicians to the possibility of this rare enzymopathy. Methods: We have studied 3 unrelated patients who presented with chronic non-spherocytic haemolytic anaemia (CNSHA) in infancy and were referred for the ORCP, a validated targeted next-generation sequencing (NGS) panel used to identify mutations in genes known to cause inherited anaemias. Results: Proband 1 was born to consanguineous parents of Pakistani origin and referred at 5 months of age with unexplained neonatal anaemia, prolonged jaundice, and later seizures. ORCP showed homozygosity for a novel mutation, c.421G>A, predicted to result in the replacement of alanine with threonine at residue 141, (p.Ala141Thr) in exon 5 of GPI. This is a moderate change to a well conserved amino acid within the GPI protein. Her younger sister was also found to be homozygous for this mutation and died unexpectedly at 2 months of age. Both parents were unaffected and confirmed to be heterozygous. Proband 2 was born to consanguineous parents of Kurdish ancestry and was referred at 13 months of age with transfusion-dependent CNSHA and jaundice. She was found to be homozygous for a novel GPI variant (c.397T>C, p.Cys133Arg), suspected to be pathogenic by in silico analysis due to a radical change in a highly conserved amino acid. Functional verification is not possible due to transfusion dependence. Parental testing is underway. Proband 3 was born to consanguineous parents of Pakistani origin and was referred aged 3 years with transfusion-dependent anaemia from birth, following severe neonatal anaemia and jaundice. The ORCP did not identify any mutations and the trio was submitted to the NIHR Bioresource whole genome sequencing programme. Analysis revealed a homozygous variant c.605A>G (p.His202Arg), predicted to be pathogenic by in silico analysis and seen only rarely in public databases (<0.001%). This variant was at a location which did not have any reads on the ORCP, explaining why it was not found by this method. Functional verification was inconclusive due to transfusion requirements. Both parents were found to have low GPI enzyme activity, consistent with a heterozygous state. Summary/Conclusion: These cases illustrate the utility of NGS panels in identification of multiple rare inherited anaemias, including GPI deficiency. Testing should be considered for patients with transfusion dependent CNSHA for which no other cause has been identified. Neurological features and consanguinity in the parents may increase suspicion. Due to the rarity of the condition, clinicians may not specifically suspect GPI deficiency in these cases, but the upcoming reconfiguration of UK genomic services and centralisation of testing criteria should allow better access to molecular testing and improved detection of these rare conditions UK-wide. The identification of specific molecular defects is helpful in providing parents with genetic counselling.