A case of kearns-sayre syndrome (the importance of enzyme staining for the diagnosis of childhood mitochondrial diseases)

Kearns- Sayre syndrome is a mitochondrial disease characterized by a triad of features including onset in persons younger than 20 years, chronic progressive external ophthalmoplegia and pigmentary degeneration of retina. It may aff ect many organ systems and a wide range of complications may develop. Cardiac conduction defects are signifi cant and preventable cause of mortality. We present a 13-year-old boy with Kearns-Sayre syndrome. His complaints were short stature, ptosis and weakness. Clinical fi ndings consisted of failure to thrive, external ophthalmoplegia, bilateral ptosis, mild hypotonia, retinitis pigmentosa and complete heart block. Cerebrospinal fl uid protein and lactate levels were increased. Cranial magnetic resonance imaging showed bilateral symmetric hyper intensities. Th e ragged red fi bers were not shown by modifi ed Gomori’s trichrome staining but succinate dehydrogenase and cytochrome oxidase combined enzyme staining demonstrated the correlation of COX negative fi bers with succinate dehydrogenase-positive ones. In addition, an increased number of mitochondria on electron microscopic examination of the skeletal muscle was determined. No mutations were found in the DNA from blood samples. Most patients with Kearns-Sayre syndrome have deleted mitochondrial DNA. However, mutations are organ specifi c and could not be demonstrated in blood samples. Electron microscopy is also of limited use in the diagnosis of mitochondrial disease as there are abnormal fi bers in normal muscle and it is the percentage of these fi bers that is important. Th e ragged red fi bers can be noticed with modifi ed Gomoris’ trichome staining in mitochondrial diseases of long duration but ragged red fi bers may not be shown with histochemical stains in muscle biopsies of children with mitochondrial myopathies. Enzyme activity revealed on muscle biopsy is therefore important for the diagnosis of mitochondrial diseases, especially in early childhood.