Muscular dystrophy

Muscular dystrophy (MD) is a group of muscle diseases that results in increasing weakening and breakdown of skeletal muscles over time. The disorders differ in which muscles are primarily affected, the degree of weakness, how fast they worsen, and when symptoms begin. Many people will eventually become unable to walk. Some types are also associated with problems in other organs.Age at onset is birth, the symptoms include general muscle weakness and possible joint deformities, disease progresses slowly, and lifespan is shortened.Congenital muscular dystrophy includes several disorders with a range of symptoms. Muscle degeneration may be mild or severe. Problems may be restricted to skeletal muscle, or muscle degeneration may be paired with effects on the brain and other organ systems.Dystrophin is part of a complex structure involving several other protein components. The 'dystrophin-glycoprotein complex' helps anchor the structural skeleton (cytoskeleton) within the muscle cells, through the outer membrane (sarcolemma) of each cell, to the tissue framework (extracellular matrix) that surrounds each cell. Due to defects in this assembly, contraction of the muscle leads to disruption of the outer membrane of the muscle cells and eventual weakening and wasting of the muscle.Miyoshi myopathy, one of the distal muscular dystrophies, causes initial weakness in the calf muscles, and is caused by defects in the same gene responsible for one form of limb-girdle muscular dystrophy.The three subtypes of Emery–Dreifuss MD are distinguishable by their pattern of inheritance: X-linked, autosomal dominant, and autosomal recessive. The X-linked form is the most common. Each type varies in prevalence and symptoms.The disease is caused by mutations in the LMNA gene, or more commonly, the EMD gene. Both genes encode for protein components of the nuclear envelope. However, how these mutations cause the pathogenesis is not well understood.Facioscapulohumeral muscular dystrophy (FSHD) initially affects the muscles of the face, shoulders, and upper arms with progressive weakness.Myotonic MD type 1 (DM1) is the most common adult form of muscular dystrophy. It results from the expansion of a short (CTG) repeat in the DNA sequence of the myotonic dystrophy protein kinase gene. Myotonic muscular dystrophy type 2 (DM2) is rarer and is a result of the expansion of the CCTG repeat in the zinc finger protein 9 gene. Muscular dystrophy (MD) is a group of muscle diseases that results in increasing weakening and breakdown of skeletal muscles over time. The disorders differ in which muscles are primarily affected, the degree of weakness, how fast they worsen, and when symptoms begin. Many people will eventually become unable to walk. Some types are also associated with problems in other organs. The muscular dystrophy group contains thirty different genetic disorders that are usually classified into nine main categories or types. The most common type is Duchenne muscular dystrophy (DMD), which typically affects males beginning around the age of four. Other types include Becker muscular dystrophy, facioscapulohumeral muscular dystrophy, and myotonic dystrophy. They are due to mutations in genes that are involved in making muscle proteins. This can occur due to either inheriting the defect from one's parents or the mutation occurring during early development. Disorders may be X-linked recessive, autosomal recessive, or autosomal dominant. Diagnosis often involves blood tests and genetic testing. There is no cure for muscular dystrophy. Physical therapy, braces, and corrective surgery may help with some symptoms. Assisted ventilation may be required in those with weakness of breathing muscles. Medications used include steroids to slow muscle degeneration, anticonvulsants to control seizures and some muscle activity, and immunosuppressants to delay damage to dying muscle cells. Outcomes depend on the specific type of disorder. Duchenne muscular dystrophy, which represents about half of all cases of muscular dystrophy, affects about one in 5,000 males at birth. Muscular dystrophy was first described in the 1830s by Charles Bell. The word 'dystrophy' is from the Greek dys, meaning 'difficult' and troph meaning 'nourish'. Gene therapy, as a treatment, is in the early stages of study in humans. The signs and symptoms consistent with muscular dystrophy are: These conditions are generally inherited, and the different muscular dystrophies follow various inheritance patterns. Muscular dystrophy can be inherited by individuals as an X-linked disorder, a recessive or dominant disorder. Furthermore, it can be a spontaneous mutation which means errors in the replication of DNA and spontaneous lesions. Spontaneous lesions are due to natural damage to DNA, where the most common are depurination and deamination. Dystrophin protein is found in muscle fiber membrane; its helical nature allows it to act like a spring or shock absorber. Dystrophin links actin in the cytoskeleton and dystroglycans of the muscle cell plasma membrane, known as the sarcolemma (extracellular). In addition to mechanical stabilization, dystrophin also regulates calcium levels.The gene for dystrophin is located on the X chromosome. In males, the lone X chromosome has only one dystrophin gene. If there's a mutation in that gene, a male's muscles will lack dystrophin and slowly degenerate; mutations in the gene for dystrophin were identified as the cause of DMD by MDA researchers in 1986. A female almost always has two dystrophin genes, one on each X chromosome, and, even if one of these isn't working, the other gene suffices to keep dystrophin levels high enough to preserve muscle function in both the heart and skeletal muscles. Nevertheless, research has shown that a small minority of females having both a working and a non-working dystrophin gene can exhibit symptoms of DMD.Recent studies on the interaction of proteins with missense mutations and its neighbors showed high degree of rigidity associated with central hub proteins involved in protein binding and flexible subnetworks having molecular functions involved with calcium. The diagnosis of muscular dystrophy is based on the results of muscle biopsy, increased creatine phosphokinase (CpK3), electromyography, and genetic testing. A physical examination and the patient's medical history will help the doctor determine the type of muscular dystrophy. Specific muscle groups are affected by different types of muscular dystrophy. Other tests that can be done are chest X-ray, echocardiogram, CT scan, and magnetic resonance image scan, which via a magnetic field can produce images whose detail helps diagnose muscular dystrophy. Quality of life can be measured using specific questionnaires.