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At a glance

Kearns-Sayre Syndrome (KSS) is a mitochondrial encephalomyopathy characterized by progressive external ophthalmoplegia, atypical retinitis pigmentosa, retinal discoloration, and cardiomyopathy (most often heart block). The most significant characteristic is the presence of a mono- or bilateral ptosis. The eye abnormalities and developmental delays are often observed before the age of 5 years in all cases. Other features include myotonia, short stature, deafness, and ataxia. This neuromuscular mitochondrial disorder affects males and females in equal numbers and the onset is typically before the age of 20 years. However, symptoms may also appear during infancy or adulthood.

Synonyms

Chronic Progressive External Ophthalmoplegia (CPEO) with Myopathy; CPEO with Ragged-Red Fibers; Progressive External Ophthalmoplegia with Ragged-Red Fibers; Kearns Syndrome; Kearns-Sayre Mitochondrial Cytopathy; Kearns-Sayre-Shy-Daroff Syndrome; Ophthalmoplegia Pigmentary Degeneration of Retina and Cardiomyopathy Syndrome; Oculo-Cranio-Somatic Syndrome; Ophthalmoplegia Plus Syndrome; Barnard-Scholz Syndrome.

History

The combination of ophthalmoplegia and retinal degeneration was first described by the two American ophthalmologists R. I. Barnard and R. O. Scholz in 1944; however, the syndrome now bears the names of the two Americans Thomas P. Kearns, a neuroophthalmologist, and George P. Sayre, an ophthalmologist, who published their findings in two patients in 1958.

Incidence

Approximately 300 cases have been reported in the literature. No sex or race predilection.

Genetic inheritance

This is a medical condition that is part of a group of disorders called mitochondrial encephalomyopathies. The presence of mitochondrial DNA deletions has been demonstrated. Incidence of affected children is dependent upon maternal mutant load. Mitochondrial DNA encodes proteins that are part of the respiratory chain complexes.

Pathophysiology

In vitro studies of mitochondrial metabolism have identified defects in the respiratory chain and in the oxidative phosphorylation system. These defects are responsible for the elevated levels of serum lactate found during and after exercise.

Diagnosis

Clinical and laboratory confirmation of elevated pyruvate and lactate. Light microscopy reveals “ragged-red muscle fibers,” which are caused by the presence of abnormal mitochondria. Electron microscopy demonstrates clusters of cells filled with abnormally enlarged mitochondria (paracrystalline inclusions). The biochemical defect often appears segmental on histochemistry.

Clinical aspects

KSS is a multiorgan disease characterized by the clinical triad of a chronic, progressive, external ophthalmoplegia, retinal pigment degeneration (with progressive loss of vision), and onset before the age of 20 years. Significant other clinical findings may include increased levels of protein in the cerebrospinal fluid, dementia, encephalopathy, cerebellar ataxia, bulbar weakness (dysphagia, which may also be related to cricopharyngeal achalasia), electroencephalographic anomalies (including seizures), sensorineural hearing loss, corneal anomalies (with increased risk of spontaneous perforation), but also cardiac anomalies (eg, high-degree atrioventricular heart blocks, QT prolongation with the risk of sudden death, dilated cardiomyopathy, mitral valve prolapse, congestive heart failure), endocrine anomalies ...

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