Kearns-Sayre syndrome (KSS) is a mitochondrial encephalomyopathy characterized by progressive external ophthalmoplegia, pigmentary retinopathy, and at least 1 of the following: heart block, cerebellar ataxia, or a cerebrospinal fluid protein level above 100 mg/dl. Serum and cerebrospinal fluid lactate and pyruvate levels are increased, and muscle biopsy shows ragged-red fibers. Onset is before 20 years of age (summary by Tanji et al., 1999; Pineda et al., 2006). [from
OMIM]