Dyskinesia such as choreiform movements, erratic limb movements, tremor, restlessness, sleep disturbance, dysmorphic features, oculo-motor apraxia, strabismus, nystagmus, axial and leg hypertonia, head tonic extension, brisk symmetric reflexes, hyperglycemia, glycosuria, and epilepsy are additional clinical features that can be observed for the cases with ID/GDD and yet carrying CACNA2D2 variants. This evidence concerns the gene CACNA2D2 and pathologic nystagmus.