The present family showed an intrafamilial phenotypic variability, already described in GLUT1-DS (18); the son manifested a classical phenotype with a developmental and epileptic encephalopathy whose diagnosis was supported by biochemical and genetic analysis, whereas his father showed only few typical GLUT1-DS features such as mild cognitive impairment, microcephaly, gait unsteadiness, and mild movement disorders (choreo-athetoid features) but no seizures, even though he harbored the same R333W mutation in SCL2A1 confirming the GLUT1-DS diagnosis. This evidence concerns the gene SLC2A1 and Dravet syndrome.