Abstracts

Rationale: GLUT1-deficiency, due to mutations in SLC2A1, can cause epilepsy with a wide range of severities. One possible mechanism for this clinical heterogeneity is the variable extent to which mutations impact GLUT1 function. To test this possibility glucose uptake was assessed in SLC2A1 variants from patients with mild to severe epilepsy. An additional aim was to exploit this knowledge to develop a simple assay of GLUT1 function that is predictive of disease severity. Methods: SLC2A1 variants were assigned to three groups. For the first group, the SLC2A1 reference sequence was drawn from NCBI and combined with four additional variants chosen from control populations. Nine variants associated with epilepsy or movement disorder with normal intellect in all known carriers formed the mild group. Finally, the severe variants group included five missense mutations associated with classical, early onset GLUT1-encephalopathy. GLUT1 was expressed in Xenopus laevis oocytes and glucose uptake measured to determine kinetics (Vmax) and affinity (Km)for each variant. Results: Full kinetic analysis revealed that disease severity inversely correlated with rate of glucose transport. Affinities of glucose binding in control and mild groups were not significantly different and because of low transport rate could not be accurately determined in the severe group. Simple kinetic analysis of glucose transport rate at 100 mM concentration was equally effective at separating the three groups. Conclusions: This study shows that disease severity can be readily explained by the extent of GLUT1 dysfunction. A simple Xenopus oocyte assay would complement genetic and clinical assessments, that include cerebrospinal fluid glucose levels and red blood cell glucose uptake. In prenatal diagnosis this simple assay would be particularly useful as standard clinical assessments are not available. Funding: NHMRC Project Grant