MERRF syndrome

MERRF syndrome (or myoclonic epilepsy with ragged red fibers) is a mitochondrial disease. It is extremely rare, and has varying degrees of expressivity owing to heteroplasmy. MERRF syndrome affects different parts of the body, particularly the muscles and nervous system. The signs and symptoms of this disorder appear at an early age, generally childhood or adolescence. The causes of MERRF syndrome are difficult to determine, but because it is a mitochondrial disorder, it can be caused by the mutation of nuclear DNA or mitochondrial DNA. The classification of this disease varies from patient to patient, since many individuals do not fall into one specific disease category. The primary features displayed on a person with MERRF include myoclonus, seizures, cerebellar ataxia, myopathy, and ragged red fibers (RRF) on muscle biopsy, leading to the disease's name. Secondary features include dementia, optic atrophy, bilateral deafness, peripheral neuropathy, spasticity, or multiple lipomata. Mitochondrial disorders, including MERRFS, may present at any age. MERRF syndrome (or myoclonic epilepsy with ragged red fibers) is a mitochondrial disease. It is extremely rare, and has varying degrees of expressivity owing to heteroplasmy. MERRF syndrome affects different parts of the body, particularly the muscles and nervous system. The signs and symptoms of this disorder appear at an early age, generally childhood or adolescence. The causes of MERRF syndrome are difficult to determine, but because it is a mitochondrial disorder, it can be caused by the mutation of nuclear DNA or mitochondrial DNA. The classification of this disease varies from patient to patient, since many individuals do not fall into one specific disease category. The primary features displayed on a person with MERRF include myoclonus, seizures, cerebellar ataxia, myopathy, and ragged red fibers (RRF) on muscle biopsy, leading to the disease's name. Secondary features include dementia, optic atrophy, bilateral deafness, peripheral neuropathy, spasticity, or multiple lipomata. Mitochondrial disorders, including MERRFS, may present at any age. An individual displaying MERRFs syndrome will manifest not only a single symptom, but patients regularly display more than one affected body part at a time. It has been observed that patients with MERRF syndrome will primarily display myoclonus as a first symptom. There may also be seizures, cerebellar ataxia and myopathy. Secondary features include dementia, optic atrophy, bilateral deafness, peripheral neuropathy, spasticity, or multiple lipomata. Additional symptoms include dementia, optic atrophy, bilateral deafness and peripheral neuropathy, spasticity, lipomatosis, and/or cardiomyopathy with Wolff Parkinson-White syndrome. Most patients will not exhibit all of these symptoms, but more than one of these symptoms will be present in a patient who has been diagnosed with MERRF disease. Due to the multiple symptoms presented by the individual, the severity of the syndrome is very difficult to evaluate. Mitochondrial disorders, including MERRF, may present at any age. Therefore, if a patient is presenting some of these symptoms, the doctor is able to narrow it down to MERRF mitochondrial disorder. The cause of MERRF disorder is due to the mitochondrial genomes mutation. This means that it is a pathogenic variant in mtDNA and is transmitted by maternal inheritance. Four point mutations in the genome can be identified which are associated with MERRF: m.A8344G, m.T8356C, m.G8361A, and m.G8363A. The point mutation m.A8344G is mostly associated with MERRF, in a study published by Paul Jose Lorenzoni from the Department of neurology at University of Panama stated that 80% of the patients with MERRF disease exhibited this point mutation. This point mutation disrupts the mitochondrial gene for tRNA-Lys, thus disrupting the synthesis of proteins essential for oxidative phosphorylation. The remaining mutations only account for 10% of cases, and the remaining 10% of the patients with MERRF did not have an identifiable mutation in the mitochondrial DNA. Many genes are involved. These genes include: