Interestingly, chronically speaking, clinical, neuroimaging, and neurophysiological features of PMM2-CDG and CACNA1A related phenotypes are also similar, including, ataxia, ocular motor disturbances (particularly nystagmus and tonic upgaze deviation), and progressive cerebellar atrophy (3, 8, 25). The gene discussed is CACNA1A; the disease is pathologic nystagmus.