Becker's Muscular Dystrophy
Becker's Muscular Dystrophy Causes
Becker's muscular dystrophy is caused by mutations in the dystrophin gene, which encodes the protein dystrophin. It is related to Duchenne muscular dystrophy in that both result from a mutation in the dystrophin gene, but in the latter, no functional dystrophin is produced, making it much more severe than BMD. It also progresses at a much slower rate as compared to Duchenne muscular dystrophy. Both muscular dystrophies have traditionally been called "X-linked" recessive diseases, but in view of modern molecular biology and identification of the dystrophin gene, it might be more appropriate to say that they are X-chromosome recessive diseases. Since women have two X chromosomes, if one of the chromosomes has the defective gene, the second X chromosome will have a working copy of the gene to compensate for it. In these cases, there are some women who have much milder symptoms because of this ability to compensate. On the other hand, because men have an X and a Y chromosome, and because they don't have another X to compensate for the defective gene, they will develop symptoms of BMD if they inherit the defective gene.
Becker's Muscular Dystrophy Definition
Becker's muscular dystrophy (BMD), also known as benign pseudohypertrophic muscular dystrophy, is an X-linked inherited disorder that involves the slowly and progressive weakness of the muscle in the legs and pelvis. It is a type of dystrophinopathy, which includes a range of muscle diseaseswhere there is insufficient dystrophin produced in the muscle cells, resulting in instability in the muscle cell membrane's structure.
Becker's Muscular Dystrophy Prevalence
BMD occurs in approximately 3-6 in 100,000 male births. Symptoms usually start to appear in males at about age 12, but may sometimes begin later. The average age of becoming wheelchair-bound is 25-30. Women rarely develop symptoms of BMD.
Becker's Muscular Dystrophy Symptoms and Signs
Symptoms include the slow progression of muscle weakness. This causes difficulty in performing muscle skills such as running, hopping, and jumping. A progressive difficulty in walking may also be experienced, coupled with frequent falling. There may also be deformities of the skeleton, specifically the chest and back (scoliosis), and of the muscles, with contractures of heels and legs, and pseudohypertrophy of calf muscles. Other symptoms include non-progressive cognitive dysfunction, fatigue, and heart disease. People with Becker's muscular dystrophy typically experience progressive weakness of the leg and pelvis muscles, which is associated with the wasting of muscle mass. Muscle weakness also occurs in other areas such as the arms and neck, but not as noticeably severe as in the lower half of the body. The patient's calf muscles initially enlarge during the ages of 5-15 (which is how the body attempts to compensate for loss of muscle strength), but the enlarged muscle tissue is eventually replaced by fat and connective tissue (pseudohypertrophy) as the legs become less used due to the use of a wheelchair). Muscle contractions also occur in the legs and heels, causing inability to use the muscles because of shortening of muscle fibers and fibrosis of connective tissue. Bones may develop abnormally, causing deformities in the skeletal structure the of the chest and other areas. Cardiomyopathy, the damage to the heart, does not occur as commonly with this disorder as it does with Duchenne's muscular dystrophy. Cognitive problems may accompany the disorder, but they are not an inevitable symptom and do not worsen as the disorder progresses.