[Disorders of folate metabolism in the Kearns-Sayre syndrome].

In 1958, Kearns and Sayre described a syndrome characterized by external ophthalmoplegia, pigmentary retinopathy and cardiac conduction disorders. Subsequent publications have reported the presence of morphologic anomalies of muscle mitochondria and a spongiform encephalopathy. The study of folate metabolism in the present case demonstrated a marked drop in cerebrospinal fluid folate levels contrasting with normal plasma levels. The origin of this anomaly could be a disturbance in the active transport system of 5-methyl tetrahydrofolate (5 CH3 THF) in the choroidal plexuses. This compound is involved in brain metabolism at different levels: synthesis of purine and pyrimidine bases, serotonin metabolism, synthesis and methylation of membrane phospholipids. Therefore a deficit in brain 5 CH3 THF levels could be implicated in the pathophysiology of the spongiform encephalopathy. In the current state of knowledge a relation between folate transfer disorders and mitochondrial anomalies is difficult to establish.