Refsum Disease Presenting with a Late-Onset Leukodystrophy.

Adult Refsum disease is an autosomal recessive peroxisomal disorder characterized by phytanic acid storage. Clinical symptoms usually begin in late childhood before the age of 20. Typical clinical presentation includes nyctalopia caused by retinitis pigmentosa, and anosmia. After 10-15 years, deafness, cerebellar ataxia, polyneuropathy, ichthyosis, and cardiac arrhythmia can occur.We report the case of a very late-onset adult Refsum disease presenting with marked cognitive decline and severe leukoencephalopathy, without peripheral nervous system involvement. Brain MRI showed a leukoencephalopathy involving the periventricular white matter, subcortical area, and the brainstem with relative sparing of juxtacortical U fibers. This was associated with severe cortical and subcortical atrophy with ventricle dilatation. MR spectroscopy showed a marked increase in the choline/NAA ratio. Elevated plasma phytanic acid level was found, whereas plasma levels of pristanic and very long chain fatty acids were normal. The patient is homozygous for a previously undescribed PHYH frameshift mutation. Whether the very unusual phenotype is related to this peculiar mutation remains unclear.