X-linked adrenoleukodystrophy presenting with positional downbeat nystagmus.

A 20-year-old man presented with dizziness and gait disturbance for approximately 2 months. Neurologic examination revealed spontaneous downbeat nystagmus (DBN), limb ataxia, and abnormal tandem gait (video on the Neurology® Web site at Neurology.org). Video-oculography showed augmented DBN during position change (figure 1). MRI revealed diffuse atrophy and signal changes in the brainstem and cerebellum (figure 2). The plasma levels of very long-chain fatty acids (C26:0 concentration, C24:0/C22:0 ratio, and C26:0/C22: 0 ratio) were elevated. Subsequent genetic testing revealed a missense mutation in the ABCD1 gene. The olivopontocerebellar form of X-linked adrenoleukodystrophy should be considered a rare but possible diagnosis in young men with dizziness and DBN.