Introduction

Glucose transporter protein 1 (GLUT1) is the principal glucose transporter of the blood–brain barrier. In GLUT1 deficiency syndrome (GLUT1DS), glucose transport into the brain is disturbed, which leads to the clinical symptomatology as well as characteristic (and diagnostic) abnormalities in cerebrospinal fluid.1 In approximately 90% of patients with GLUT1DS, heterozygous mutations in the SLC2A1 gene, encoding the GLUT1 protein, can be demonstrated.1 So far, this is the only gene known to be associated with this condition. The classic phenotype of GLUT1DS includes microcephaly, mild to severe developmental delay, infantile-onset drug-resistant epilepsy, and movement disorders, including spasticity, ataxia and dystonia.1 Recognising GLUT1DS is crucial because it can be treated with the ketogenic diet, as ketone bodies serve as alternative energy source for the brain.1

In the past decade, the range of clinical syndromes associated with GLUT1DS has expanded tremendously. Various paroxysmal or episodic disorders have now been described in patients with GLUT1DS, including several seizure types, paroxysmal lethargy, autonomic attacks with sweating and yawning, hemiplegic migraine and eye movement disorders. Moreover, many different movement disorders, including ataxia and intention tremor, dystonia, chorea, spasticity, myoclonus and nocturnal painful muscle cramps in the legs, are a recognised part of the clinical spectrum and included in the phenotype of many individual patients.1 2 These movement disorders can be continuous, paroxysmal or …