Mitochondria, Muscle
DNA, Mitochondrial
Myopathies, Structural, Congenital
Distal Myopathies
Myopathies, Nemaline
Myositis, Inclusion Body
Human deafness dystonia syndrome is a mitochondrial disease. (1/210)
The human deafness dystonia syndrome results from the mutation of a protein (DDP) of unknown function. We show now that DDP is a mitochondrial protein and similar to five small proteins (Tim8p, Tim9p, Tim10p, Tim12p, and Tim13p) of the yeast mitochondrial intermembrane space. Tim9p, Tim10p, and Tim12p mediate the import of metabolite transporters from the cytoplasm into the mitochondrial inner membrane and interact structurally and functionally with Tim8p and Tim13p. DDP is most similar to Tim8p. Tim8p exists as a soluble 70-kDa complex with Tim13p and Tim9p, and deletion of Tim8p is synthetically lethal with a conditional mutation in Tim10p. The deafness dystonia syndrome thus is a novel type of mitochondrial disease that probably is caused by a defective mitochondrial protein-import system. (+info)Rapid progression of cardiomyopathy in mitochondrial diabetes. (2/210)
Cardiac involvement and its clinical course in a diabetic patient with a mitochondrial tRNA(Leu)(UUR) mutation at position 3243 is reported in a 54-year-old man with no history of hypertension. At age 46, an electrocardiogram showed just T wave abnormalities. At age 49, it fulfilled SV1 + RV5 or 6>35 mm with strain pattern. At age 52, echocardiography revealed definite left ventricular (LV) hypertrophy, and abnormally increased mitochondria were shown in biopsied endomyocardial specimens. He was diagnosed as having developed hypertrophic cardiomyopathy associated with the mutation. However, at age 54, SV1 and RV5,6 voltages were decreased, and echocardiography showed diffuse decreased LV wall motion and LV dilatation. Because he had mitochondrial diabetes, the patient's heart rapidly developed hypertrophic cardiomyopathy, and then it seemed to be changing to a dilated LV with systolic dysfunction. Rapid progression of cardiomyopathy can occur in mitochondrial diabetes. (+info)Relaxed replication of mtDNA: A model with implications for the expression of disease. (3/210)
Heteroplasmic mtDNA defects are an important cause of human disease with clinical features that primarily involve nondividing (postmitotic) tissues. Within single cells the percentage level of mutated mtDNA must exceed a critical threshold level before the genetic defect is expressed. Although the level of mutated mtDNA may alter over time, the mechanism behind the change is not understood. It currently is not possible to directly measure the level of mutant mtDNA within living cells. We therefore developed a mathematical model of human mtDNA replication, based on a solid foundation of experimentally derived parameters, and studied the dynamics of intracellular heteroplasmy in postmitotic cells. Our simulations show that the level of intracellular heteroplasmy can vary greatly over a short period of time and that a high copy number of mtDNA molecules delays the time to fixation of an allele. We made the assumption that the optimal state for a cell is to contain 100% wild-type molecules. For cells that contain pathogenic mutations, the nonselective proliferation of mutant and wild-type mtDNA molecules further delays the fixation of both alleles, but this leads to a rapid increase in the mean percentage level of mutant mtDNA within a tissue. On its own, this mechanism will lead to the appearance of a critical threshold level of mutant mtDNA that must be exceeded before a cell expresses a biochemical defect. The hypothesis that we present is in accordance with the available data and may explain the late presentation and insidious progression of mtDNA diseases. (+info)Diagnostic utility of metabolic exercise testing in a patient with cardiovascular disease. (4/210)
Disproportionate exercise limitation in patients with cardiovascular disease is a common problem faced by clinical cardiologists and other physicians. Symptoms may be attributed to psychological factors or hypothetical pathophysiological mechanisms that are difficult to confirm clinically. This case report describes how the use of metabolic exercise testing in a 28 year old woman with morphologically and haemodynamically mild hypertrophic cardiomyopathy and severe exercise limitation led to the diagnosis of an alternative cause for the patient's symptoms, namely a primary disturbance of the mitochondrial respiratory chain probably caused by a nuclear encoded gene defect. (+info)Enzyme histochemical study of germanium dioxide-induced mitochondrial myopathy in rats. (5/210)
The purpose of this study were 1) to determine the earliest pathological changes of germanium dioxide (GeO2)-induced myopathy; 2) to determine the pathomechanism of GeO2-induced myopathy; and 3) to determine the minimal dose of GeO2 to induce myopathy in rats. One hundred and twenty five male and female Sprague-Dawley rats, each weighing about 150 gm, were divided into seven groups according to daily doses of GeO2. Within each group, histopathological studies were done at 4, 8, 16, and 24 weeks of GeO2 administration. Characteristic mitochondrial myopathy was induced in the groups treated daily with 10 mg/kg of GeO2 or more. In conclusion, the results were as follows: 1) The earliest pathological change on electron microscope was the abnormalities of mitochondrial shape, size and increased number of mitochondria; 2) The earliest pathological change on light microscope was the presence of ragged red fibers which showed enhanced subsarcolemmal succinate dehydrogenase and cytochrome c oxidase reactivity; 3) GeO2 seemed to affect the mitochondrial oxidative metabolism of muscle fibers; 4) GeO2 could induce mitochondrial myopathy with 10 mg/kg of GeO2 for 4 weeks or less duration in rats. (+info)Low brain intracellular free magnesium in mitochondrial cytopathies. (6/210)
The authors studied, by in vivo phosphorus magnetic resonance spectroscopy (31P-MRS), the occipital lobes of 19 patients with mitochondrial cytopathies to clarify the functional relation between energy metabolism and concentration of cytosolic free magnesium. All patients displayed defective mitochondrial respiration with low phosphocreatine concentration [PCr] and high inorganic phosphate concentration [Pi] and [ADP]. Cytosolic free [Mg2+] and the readily available free energy (defined as the actual free energy released by the exoergonic reaction of ATP hydrolysis, i.e., deltaG(ATPhyd)) were abnormally low in all patients. Nine patients were treated with coenzyme Q10 (CoQ), which improved the efficiency of the respiratory chain, as shown by an increased [PCr], decreased [Pi] and [ADP], and increased availability of free energy (more negative value of deltaG(ATPhyd)). Treatment with CoQ also increased cytosolic free [Mg2+] in all treated patients. The authors findings demonstrate low brain free [Mg2+] in our patients and indicate that it resulted from failure of the respiratory chain. Free Mg2+ contributes to the absolute value of deltaG(ATPhyd). The results also are consistent with the view that cytosolic [Mg2+] is regulated in the intact brain cell to equilibrate, at least in part, any changes in rapidly available free energy. (+info)Gene shifting: a novel therapy for mitochondrial myopathy. (7/210)
Mutations in mitochondrial DNA (mtDNA) are the most frequent causes of mitochondrial myopathy in adults. In the majority of cases mutant and wild-type mtDNAs coexist, a condition referred to as mtDNA heteroplasmy; however, the relative frequency of each species varies widely in different cells and tissues. Nearly complete segregation of mutant and wild-type mtDNAs has been observed in the skeletal muscle of many patients. In such patients mutant mtDNAs pre-dominate in mature myofibers but are rare or undetectable in skeletal muscle satellite cells cultured in vitro. This pattern is thought to result from positive selection for the mutant mtDNA in post-mitotic myofibers and loss of the mutant by genetic drift in satellite cells. Satellite cells are dormant myoblasts that can be stimulated to re-enter the cell cycle and fuse with existing myofibers in response to signals for muscle growth or repair. We tested whether we could normalize the mtDNA genotype in mature myofibers in a patient with mitochondrial myopathy by enhancing the incorporation of satellite cells through regeneration following injury or muscle hypertrophy, induced by either eccentric or concentric resistance exercise training. We show a remarkable increase in the ratio of wild-type to mutant mtDNAs, in the proportion of muscle fibers with normal respiratory chain activity and in muscle fiber cross-sectional area after a short period of concentric exercise training. These data show that it is possible to reverse the molecular events that led to expression of metabolic myopathy and demonstrate the effectiveness of this form of 'gene shifting' therapy. (+info)Suppression of a mitochondrial tRNA gene mutation phenotype associated with changes in the nuclear background. (8/210)
We previously have characterized a pathogenic mtDNA mutation in the tRNAAsn gene. This mutation (G5703A) was associated with a severe mitochondrial protein synthesis defect and a reduction in steady-state levels of tRNAAsn. We now show that, although transmitochondrial cybrids harboring homoplasmic levels of the mutation do not survive in galactose medium, several galactose-resistant clones could be obtained. These cell lines had restored oxidative phosphorylation function and 2-fold higher steady-state levels of tRNAAsn when compared with the parental mutant cell line. The revertant lines contained apparently homoplasmic levels of the mutation and no other detectable alteration in the tRNAAsn gene. To investigate the origin of the suppression, we transferred mtDNA from the revertants (143B/206 TK-) to a different nuclear background (143B/207 TK-, 8AGr). These new transmitochondrial cybrids became defective once again in oxidative phosphorylation and regained galactose sensitivity. However, galactose-resistant clones could also be obtained by growing the 8AGr transmitochondrial cybrids under selection. Because the original rate of reversion was higher than that expected by a classic second site nuclear mutation, and because of the aneuploid features of these cell lines, we searched for the presence of chromosomal alterations that could be associated with the revertant phenotype. These studies, however, did not reveal any gross changes. Our results suggest that modulation of the dosage or expression of unknown nuclear-coded factor(s) can compensate for a pathogenic mitochondrial tRNA gene mutation, suggesting new strategies for therapeutic intervention. (+info)Mitochondrial myopathies are a group of genetic disorders caused by mutations in the mitochondrial DNA or nuclear DNA that affect the function of the mitochondria, which are the energy-producing structures in cells. These mutations can result in impaired muscle function and other symptoms, depending on the specific type and severity of the disorder.
Mitochondrial myopathies can present at any age and can cause a range of symptoms, including muscle weakness, exercise intolerance, fatigue, muscle pain, and difficulty with coordination and balance. Some people with mitochondrial myopathies may also experience neurological symptoms such as seizures, developmental delays, and hearing or vision loss.
The diagnosis of mitochondrial myopathies typically involves a combination of clinical evaluation, muscle biopsy, genetic testing, and other diagnostic tests to assess mitochondrial function. Treatment is generally supportive and may include physical therapy, medications to manage symptoms, and nutritional support. In some cases, specific therapies such as vitamin or coenzyme Q10 supplementation may be recommended based on the underlying genetic defect.
Mitochondria in muscle, also known as the "powerhouses" of the cell, are organelles that play a crucial role in generating energy for muscle cells through a process called cellular respiration. They convert the chemical energy found in glucose and oxygen into ATP (adenosine triphosphate), which is the main source of energy used by cells.
Muscle cells contain a high number of mitochondria due to their high energy demands for muscle contraction and relaxation. The number and size of mitochondria in muscle fibers can vary depending on the type of muscle fiber, with slow-twitch, aerobic fibers having more numerous and larger mitochondria than fast-twitch, anaerobic fibers.
Mitochondrial dysfunction has been linked to various muscle disorders, including mitochondrial myopathies, which are characterized by muscle weakness, exercise intolerance, and other symptoms related to impaired energy production in the muscle cells.
Mitochondrial DNA (mtDNA) is the genetic material present in the mitochondria, which are specialized structures within cells that generate energy. Unlike nuclear DNA, which is present in the cell nucleus and inherited from both parents, mtDNA is inherited solely from the mother.
MtDNA is a circular molecule that contains 37 genes, including 13 genes that encode for proteins involved in oxidative phosphorylation, a process that generates energy in the form of ATP. The remaining genes encode for rRNAs and tRNAs, which are necessary for protein synthesis within the mitochondria.
Mutations in mtDNA can lead to a variety of genetic disorders, including mitochondrial diseases, which can affect any organ system in the body. These mutations can also be used in forensic science to identify individuals and establish biological relationships.
Myositis is a medical term that refers to inflammation of the muscle tissue. This condition can cause various symptoms, including muscle weakness, pain, swelling, and stiffness. There are several types of myositis, such as polymyositis, dermatomyositis, and inclusion body myositis, which have different causes and characteristics.
Polymyositis is a type of myositis that affects multiple muscle groups, particularly those close to the trunk of the body. Dermatomyositis is characterized by muscle inflammation as well as a skin rash. Inclusion body myositis is a less common form of myositis that typically affects older adults and can cause both muscle weakness and wasting.
The causes of myositis vary depending on the type, but they can include autoimmune disorders, infections, medications, and other medical conditions. Treatment for myositis may involve medication to reduce inflammation, physical therapy to maintain muscle strength and flexibility, and lifestyle changes to manage symptoms and prevent complications.
Muscular diseases, also known as myopathies, refer to a group of conditions that affect the functionality and health of muscle tissue. These diseases can be inherited or acquired and may result from inflammation, infection, injury, or degenerative processes. They can cause symptoms such as weakness, stiffness, cramping, spasms, wasting, and loss of muscle function.
Examples of muscular diseases include:
1. Duchenne Muscular Dystrophy (DMD): A genetic disorder that results in progressive muscle weakness and degeneration due to a lack of dystrophin protein.
2. Myasthenia Gravis: An autoimmune disease that causes muscle weakness and fatigue, typically affecting the eyes and face, throat, and limbs.
3. Inclusion Body Myositis (IBM): A progressive muscle disorder characterized by muscle inflammation and wasting, typically affecting older adults.
4. Polymyositis: An inflammatory myopathy that causes muscle weakness and inflammation throughout the body.
5. Metabolic Myopathies: A group of inherited disorders that affect muscle metabolism, leading to exercise intolerance, muscle weakness, and other symptoms.
6. Muscular Dystonias: Involuntary muscle contractions and spasms that can cause abnormal postures or movements.
It is important to note that muscular diseases can have a significant impact on an individual's quality of life, mobility, and overall health. Proper diagnosis and treatment are crucial for managing symptoms and improving outcomes.
Congenital structural myopathies are a group of inherited genetic disorders that affect the structure and function of skeletal muscles. These conditions are present at birth or develop in early infancy and are caused by genetic mutations that lead to abnormalities in the muscle contractile apparatus, including the sarcomere, muscle filaments, and muscle membrane.
The structural abnormalities can affect the muscle fibers' ability to generate force, leading to muscle weakness, hypotonia (low muscle tone), and other symptoms. The severity of the condition can vary widely, from mild to severe, depending on the specific type of myopathy and the extent of muscle involvement.
Examples of congenital structural myopathies include:
1. Congenital fiber-type disproportion (CFTD): a condition characterized by small, atrophic type 1 muscle fibers and normal or enlarged type 2 fibers.
2. Central core disease (CCD): a condition caused by mutations in the ryanodine receptor gene, which leads to the formation of abnormal structures called cores within the muscle fibers.
3. Nemaline myopathy: a condition characterized by the presence of rod-shaped structures called nemalines in the muscle fibers.
4. Myotubular myopathy: a condition caused by mutations in the myotubularin gene, which leads to abnormalities in the muscle fiber nuclei and weakened muscle function.
5. Congenital muscular dystrophy (CMD): a group of conditions characterized by muscle weakness, hypotonia, and joint contractures, often associated with structural abnormalities in the muscle membrane or extracellular matrix.
Diagnosis of congenital structural myopathies typically involves a combination of clinical evaluation, genetic testing, and muscle biopsy. Treatment is generally supportive and may include physical therapy, orthotics, and assistive devices to help manage symptoms and improve function. In some cases, medications or surgical interventions may be necessary to address specific complications.
Distal myopathies are a group of rare genetic muscle disorders that primarily affect the muscles of the hands, feet, and lower legs. These myopathies are characterized by progressive weakness and wasting (atrophy) of the distal muscles, which are located further from the center of the body. The onset of symptoms can vary widely, ranging from early childhood to late adulthood.
There are several different types of distal myopathies, each caused by mutations in specific genes that affect muscle function. Some common forms include:
1. Nonaka Distal Myopathy: This form is caused by mutations in the GNE gene and typically presents in the third or fourth decade of life with weakness and wasting of the ankle dorsiflexors, foot extensors, and wrist and finger extensors.
2. Miyoshi Distal Myopathy: This form is caused by mutations in the DYSF gene and affects the calf muscles initially, followed by weakness in other distal muscles over time.
3. Welander Distal Myopathy: This form is caused by mutations in the TIA1 gene and typically presents in adulthood with weakness and wasting of the hand and forearm muscles.
4. Laing Distal Myopathy: This form is caused by mutations in the CAV3 gene and affects the anterior compartment of the lower leg, resulting in foot drop and weakness of the ankle dorsiflexors.
5. Gowers Distal Myopathy: This form is caused by mutations in the HNRNPDL gene and typically presents in adulthood with weakness and wasting of the hand and forearm muscles, as well as foot drop.
There is no cure for distal myopathies, but treatment can help manage symptoms and improve quality of life. Physical therapy, bracing, and orthotics may be used to support weakened muscles and maintain mobility. In some cases, medications such as corticosteroids or immunosuppressants may be prescribed to reduce muscle inflammation and slow disease progression.
Nemaline myopathy is a genetic muscle disorder characterized by the presence of rod-like structures called nemalines in the muscle fibers. These rods, which are composed of accumulated protein, can be observed under a microscope in biopsied muscle tissue. The condition is typically present at birth or appears in early childhood and is often associated with muscle weakness, hypotonia (low muscle tone), and delayed motor development.
There are several types of nemaline myopathy, which vary in severity and age of onset. Some individuals with the disorder may have only mild symptoms and be able to lead relatively normal lives, while others may experience significant disability and require assistance with daily activities. The condition can also affect the heart and respiratory muscles, leading to serious complications.
Nemaline myopathy is caused by mutations in one of several genes that are involved in the formation and maintenance of muscle fibers. These genetic defects lead to abnormalities in the structure and function of the muscle fibers, resulting in the characteristic symptoms of the disorder. There is currently no cure for nemaline myopathy, but treatment is focused on managing the symptoms and improving quality of life. This may include physical therapy, assistive devices, and respiratory support, as well as medications to help manage muscle spasticity and other complications.
Inclusion body myositis (IBM) is a rare inflammatory muscle disease characterized by progressive weakness and wasting (atrophy) of skeletal muscles. The term "inclusion body" refers to the presence of abnormal protein accumulations within muscle fibers, which are observed under a microscope during muscle biopsy. These inclusions are primarily composed of aggregated forms of amyloid-β and tau proteins, similar to those found in neurodegenerative disorders like Alzheimer's disease.
IBM typically affects individuals over 50 years old, and it is more common in men than women. The disease usually starts with weakness in the wrist and finger flexors, making it difficult to perform tasks such as gripping, buttoning shirts, or lifting objects. Over time, the weakness spreads to other muscle groups, including the thigh muscles (quadriceps), resulting in difficulty climbing stairs or rising from a seated position.
The exact cause of inclusion body myositis remains unclear; however, both immune-mediated and degenerative mechanisms are believed to contribute to its pathogenesis. Currently, there is no cure for IBM, and treatment options are primarily aimed at managing symptoms and improving quality of life. Immunosuppressive medications may be used to target the inflammatory component of the disease; however, their efficacy varies among patients. Physical therapy and exercise programs can help maintain muscle strength and function as much as possible.