Erythrocyte 3‐O‐methyl‐D‐glucose uptake assay for diagnosis of glucose‐transporter‐protein syndrome

Abstract

Glucose transport into the brain is mediated by a facilitative glucose-transporter protein, GLUT-1. A GLUT-1 defect results in the Glucose-Transporter-Protein Syndrome (GTPS), characterized by infantile epilepsy, developmental delay, and acquired microcephaly. The diagnosis is currently based on clinical features, low to normal lactate levels and low glucose levels (hypoglycorrhachia) in the cerebrospinal fluid, and the demonstration of impaired GLUT-1 function in erythrocytes as described here. Blood samples were collected in sodium-heparin or citrate-phosphate-dextrose solution and uptake of 14C-labeled 3-O-Methyl-D-glucose (3OMG into erythrocytes (0.5 mmol/L 3OMG; 1 microCi/mL) was measured at 4C and pH 7.4. Three-OMG influx was terminated at 5-second intervals, washed cells were lysed, and uptake was quantitated by liquid scintillation counting. Patients' uptake (n = 22) was 44 +/- 8% of controls (100 +/- 22%, n = 70). Statistical analyses showed an uptake cut-off point at 60% uptake, a sensitivity of 86% (95%-confidence interval 78 to 94%), and a specificity of 97% (95%-confidence interval 93 to 100%). Gender, age, and ketosis did not influence 3OMG uptake. This assay provides a reproducible and accurate laboratory test for diagnosing the GTPS.

Facilitated glucose transporter protein type 1 (GLUT1) deficiency syndrome: impaired glucose transport into brain – a review

“…In the description of the original assay, glucose uptake in patients (n=22) was 44±8% of controls (100±22%, n=70). Statistical analyses showed an uptake cut-off point at 60% uptake, a sensitivity of 86%, and a specificity of 97% [42]. Gender, age, and ketosis did not influence the method.…”

“…The diet should be started if the disease is suspected on account of clinical features and hypoglycorrhachia, as ketosis does not interfere with GLUT1 analyses [42,43].…”

“…With the exception of fluorescence in-situ hybridisation analyses, investigations can be performed on a 5 ml blood sample collected in special tubes containing citrate-dextrosephosphate solution [42,44,70]. Samples should be taken from patient and parents and shipped at 4°C via express carrier to the laboratory for immediate analysis.…”

“…As the human erythrocyte glucose transporter is immunochemically identical to the human brain GLUT1 [19], glucose uptake studies into erythrocytes with nonmetabolisable 3-O-methyl-D-glucose represent transendothelial glucose transport across the BBB [42]. Intact erythrocytes and careful blood-drawing and shipment to avoid haemolysis are essential.…”

Glucose Transporter Type I Deficiency and Other Glucose Flux Disorders

“…The assay is relatively specific and sensitive for GLUT1 deficiency syndrome, but false negatives have been obtained. 86 …”