Among these, 13 genes encode proteins of the electron transport chain (abbreviated "ETC"), 22 encode transfer RNA (tRNA), and two encode the large and small subunits that form ribosomal RNA (rRNA). The 13 proteins involved in the ETC of the mitochondrion are necessary for oxidative phosphorylation. Mutations in these proteins results in impaired energy production by mitochondria. This cellular energy deficit manifests most readily in tissues that rely heavily upon aerobic metabolism such as the brain, skeletal and cardiac muscles, sensory organs, and kidneys. This is one factor involved in the presentation of mitochondrial diseases.There are other factors involved in the manifestation of a mitochondrial disease besides the size and location of a mutation. Mitochondria replicate during each cell division during gestation and throughout life. Because the mutation in mitochondrial disease most often occurs early in gestation in these diseases, only those mitochondria in the mutated lineage are defective. This results in an uneven distribution of dysfunctional mitochondria within each cell, and among different tissues of the body. This describes the term heteroplasmic which is characteristic of mitochondrial diseases including KSS. The distribution of mutated mtDNA in each cell, tissue, and organ, is dependent on when and where the mutation occurs. This may explain why two patients with an identical mutation in mtDNA can present with entirely different phenotypes and in turn different syndromes. A publication in 1992 by Fischel-Ghodsian et al. identified the same 4,977-bp deletion in mtDNA in two patients presenting with two entirely different diseases.
Administration of 60–120 mg of coenzyme Q10 for three months resulted in normalization of lactate and pyruvate levels, improvement of previously diagnosed first degree AV block, and improvement of ocular movements.A screening ECG is recommended in all patients presenting with CPEO. In KSS, implantation of pacemaker is advised following the development of significant conduction disease, even in asymptomatic patients.Screening for endocrinologic disorders should be performed, including measuring serum glucose levels, thyroid function tests, calcium and magnesium levels, and serum electrolyte levels. Hyperaldosteronism is seen in 3% of KSS patients. History
The triad of CPEO, bilateral pigmentary retinopathy, and cardiac conduction abnormalities was first described in a case report of two patients in 1958 by Thomas P. Kearns (1922–2011), MD., and George Pomeroy Sayre (1911–1992), MD. A second case was published in 1960 by Jager and co-authors reporting these symptoms in a 13-year-old boy. Previous cases of patients with CPEO dying suddenly had been published, occasionally documented as from a cardiac dysrhythmia. Other cases had noted a peculiar pigmentation of the retina, but none of these publications had documented these three pathologies occurring together as a genetic syndrome. Kearns published a defining case in 1965 describing nine unrelated cases with this triad. In 1988, the first connection was made between KSS and large-scale deletions of muscle mitochondrial DNA (abbreviated mtDNA)  Since this discovery, numerous deletions in mitochondrial DNA have been linked to the development of KSS. References
External links
kearns_sayre at NINDS
Kearns Sayre syndrome at NIHs Office of Rare Diseases