SLC2A1 and Global developmental delay: SLC2A1 haploinsufficiency is responsible for a wide spectrum of neurological abnormalities, ranging from classic GLUT1-DS (a severe, infantile-onset encephalopathy causing epilepsy, microcephaly, developmental delay and complex movement disorders) to milder forms, showing variable combinations of cognitive disabilities, different seizure types, abnormal movements and various paroxysmal non-epileptic motor disorders [179].