Glucose, the main source of energy for the brain, is transported across the blood–brain barrier by glucose transporter protein type 1 (GLUT1).1, 2, 3In GLUT1 deficiency syndrome (GLUT1DS), glucose uptake into the brain is limited due to decreased glucose transport capacity, leaving the brain with a permanent energy deficit. Here, SLC2A1 is linked to GLUT1 deficiency syndrome.