Glut1 deficiency syndrome and erythrocyte glucose uptake assay

OBJECTIVE: The Glut1 deficiency syndrome (Glut1 DS) phenotype has expanded dramatically since first described in 1991. Hypoglycorrhachia and decreased erythrocyte 3-OMG uptake are confirmatory laboratory biomarkers. The objective is to expand previous observations regarding the diagnostic value of the uptake assay. METHODS: One hundred and nine suspected cases of Glut-1 DS were studied. All cases had a consistent clinical picture and hypoglycorrhachia. The uptake assay was decreased in 74 cases (group 1) and normal in 35 cases (group 2). We identified disease-causing mutations in 70 group 1 patients (95%) and one group 2 patient (3%). RESULTS: The cut-off for an abnormally low uptake value was increased from 60% to 74% with a corresponding sensitivity of 99% and specificity of 100%. The correlation between the uptake values for the time-curve and the kinetic concentration curve were strongly positive (R(2) = 0.85). Significant group differences were found in CSF glucose and lactate values, tone abnormalities, and degree of microcephaly. Group 2 patients were less affected in all domains. We also noted a significant correlation between the mean erythrocyte 3-OMG uptake and clinical severity (R(2) = 0.94). INTERPRETATION: These findings validate the erythrocyte glucose uptake assay as a confirmatory functional test for Glut1 DS and as a surrogate marker for GLUT1 haploinsufficiency.