An established example of the application of the precision medicine concept is in the management of GLUT-1 deficiency, a genetic metabolic encephalopathy due to mutations in the SLC2A1 gene, which encodes the glucose type I transporter (GLUT-1), resulting in impaired transport of glucose across the blood-brain barrier. Here, SLC2A1 is linked to hyperinsulinemic hypoglycemia, familial, 4.