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Histochemical and molecular genetic study of MELAS and MERRF in Korean patients
Dae Seong Kim1, Dae Soo Jung, Kyu Hyun Park
1Department of Neurology and Biochemistry, College of Medicine, Pusan National University, 10, 1-ga, Ami-dong, Seo-gu, Pusan 602-739, Korea. dskim@pusan.ac.kr
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.
Insights
Mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episode (MELAS) and myoclonic epilepsy and ragged-red fibers (MERRF) are linked to tRNA gene mutations. Histochemistry and muscle DNA analysis are crucial for diagnosing these rare mitochondrial disorders.
Area of Science:
- Mitochondrial genetics
- Neuromuscular disorders
- Molecular diagnostics
Background:
- Mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episode (MELAS) and myoclonic epilepsy and ragged-red fibers (MERRF) are rare genetic disorders.
- These conditions result from point mutations in mitochondrial tRNA genes.
Purpose of the Study:
- To investigate the pathogenetic mechanisms of MELAS and MERRF.
- To correlate clinical findings with molecular genetic mutations.
Main Methods:
- Histochemical staining (e.g., succinyl dehydrogenase, cytochrome oxidase) of muscle biopsies.
- Ultrastructural analysis via electron microscopy.
- Molecular genetic analysis including PCR-RFLP and gene sequencing of tRNA genes from muscle and blood.
Main Results:
- MELAS patients showed A3243G mutations with specific histochemical findings (SSVs, COX-positive RRFs).
- MERRF patients exhibited A8344G mutations without SSVs or COX-positive RRFs.
- Identical mutations were found in MERRF families; MELAS mutations were not detected in blood, suggesting low mutant load.
Conclusions:
- Histochemical stains like COX are valuable for differentiating mitochondrial diseases.
- Molecular studies on muscle tissue are essential for confirming mitochondrial DNA (mtDNA) mutations in MELAS and MERRF.
- The study highlights the utility of combined histochemical and molecular approaches for diagnosing rare mitochondrial disorders.