Classic glucose transporter type 1 deficiency syndrome (Glut1 DS) is a rare genetic disorder caused by a mutation in the SLC2A1 gene. This gene provides instructions for making a protein called glucose transporter type 1 (GLUT1). This protein is responsible for transporting glucose, a sugar that provides energy to cells, from the bloodstream into the brain. People with Glut1 DS have a deficiency of GLUT1, which prevents glucose from entering the brain. This leads to a variety of neurological symptoms, including seizures, developmental delays, and movement disorders.