Histochemical and Molecular Genetic Study of MELAS and MERRF in Korean Patients

Abstract

Mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episode (MELAS) and myoclonic epilepsy and ragged-red fibers (MERRF) are rare disorders caused by point mutation of the tRNA gene of the mitochondrial genome. To understand the pathogenetic mechanism of MELAS and MERRF, we studied four patients. Serially sectioned frozen muscle specimens with a battery of histochemical stains were reviewed under light microscope and ultrastructural changes were observed under electron microscope. The polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) analysis was performed and the tRNA genes were sequenced to confirm mutations. In two patients with MELAS, strongly succinyl dehydrogenase positive blood vessels (SSVs) and many cytochrome oxidase (COX) positive ragged-red fibers (RRFs) were observed, and A3243G mutations were found from the muscle samples. In two patients with MERRF, neither SSV nor COX positive RRFs were seen and A8344G mutations were found from both muscle and blood samples. In the two MERRF families, the identical mutation was observed among family members. The failure to detect the mutation in blood samples of the MELAS suggests a low mutant load in blood cells. The histochemical methods including COX stain are useful for the confirmation and differentiation of mitochondrial diseases. Also, molecular biological study using muscle sample seems essential for the confirmation of the mtDNA mutation.

Investigation of Common Mitochondrial Point Mutations in Korea

“…Therefore, selection of the affected organ or tissues with heavy mutation loads is also important in increasing the detection sensitivity. Southern blotting is another method that can increase the sensitivity in low mutant‐loaded individuals 9,10. Despite all of these limitations, we found that the A3243G and A8344G mutations are the most common mtDNA mutations in Korea, which can be used as a guide to efficiently screen mitochondrial diseases.…”

“…Among the reported mutations, A3243G and A8344G are the most common pathogenic mutations of mtDNA. They are genetically and phenotypically distinct 9,10. The A3243G mutation was originally described in a patient with MELAS, which is clinically characterized by recurrent stroke‐like episodes, migraine, nausea, and vomiting.…”

Genetics of Mitochondrial Myopathies

“…1A). 19,20) It is a muscle fiber in which compensatory proliferation of dysfunctional mitochondria accumulates in subsarcolemmal and intermyofibrillar space. The bright red masses around the sides of the muscle fiber contrasts with green sarcoplasm just as the name describes.…”

“…RRFs , ragged blue fibers, and COXnegative fibers may or may not coincide. 19) Other frequent histologic findings of mitochondrial myopathies include typespecific muscle fiber atrophy and fibers with lipid or glycogen accumulation. Electron microscopy reveals mito chondrial proliferation in subsarcolemmal or intermyofibrillar space.…”

“…1D). 19) The studies on MELAS pathogenesis focus on the most frequent m.3243A>G mutation. It is the 14th nucleotide in tRNA Leu(UUR) gene and in highly conserved area.…”