Downbeat nystagmus indicates cerebellar or brain-stem lesions in vitamin B12 deficiency.

Two cases of vitamin B12 deficiency caused by gastric atrophy are described. Together with the neuropsychiatric features usually associated with this condition, a downbeat nystagmus syndrome was observed. It is concluded that vitamin B12 deficiency may also result in lesions to those cerebellar or brain-stem structures that are generally assumed to cause downbeat nystagmus.