Choroid plexus failure in the Kearns-Sayre syndrome.

The Kearns-Sayre syndrome is a mitochondrial disorder (generally due to mitochondrial DNA deletions) that causes ophthalmoplegia, retinopathy, ataxia and brain abnormalities such as leukoencephalopathy. In this syndrome, the choroid plexus epithelial cells, unlike brain cells, are greatly enlarged and granular, consistent with their inability to adequately transport folate from blood into cerebrospinal fluid (CSF), and homovanillic acid (a dopamine metabolite) from CSF into blood. This inability to transport folates from blood into CSF (and brain) adequately, causes cerebral folate deficiency that can be partially reversed by very high doses of reduced folates. The Kearns-Sayre syndrome is a disease that interferes with key choroid plexus functions and is a cause of generalized choroid plexus failure.