![]() ![]() The second possibility is that a child with DMD has a new genetic mutation that arose in one of his mother’s egg cells. Perhaps no male children were born with the disease, or, even if a boy in an earlier generation was affected, relatives may not have known what disease he had. The first is that the genetic mutation leading to DMD may have existed in the females of a family for some generations without anyone knowing. DMD carriers are at risk for cardiomyopathy.Īlthough DMD often runs in a family, it is possible for a family with no history of DMD to suddenly have a son with the disease. Carriers may not have any disease symptoms but can have a child with the mutation or the disease. Each of her daughters has a 50 percent chance of inheriting the mutation and being a carrier. Girls get two X chromosomes, one from each parent.Įach son born to a woman with a dystrophin mutation on one of her two X chromosomes has a 50 percent chance of inheriting the flawed gene and having DMD. Every boy inherits an X chromosome from his mother and a Y chromosome from his father, which is what makes him male. Inheritance in DMDĭMD is inherited in an X-linked pattern because the gene that can carry a DMD-causing mutation is on the X chromosome. Lack of dystrophin causes muscle damage and progressive weakness, beginning in early childhood. Loss of dystrophin displaces these molecules, with consequent disruptions in their functions. In addition to its force-transfer role, dystrophin provides the scaffold for holding numerous molecules in place near the cell membrane. Fibrous tissue begins to form in the muscle, and the body’s immune system increases inflammation. The absence of dystrophin sets in motion a cascade of harmful effects. Production of the entire protein stops when the mutation is encountered. Many cases of DMD are caused by mutations in the part of the gene that encodes this middle section. The repeated spectrin units in the middle of the protein play an important role in linking the two ends, but studies have shown that the exact number of these units is not critical for the function of the protein as a whole. The long middle section, called the rod domain, is taken up by a series of repeating units called spectrin repeats. One end is specialized for linking to the muscle cell interior and the other end is specialized for linking to a variety of proteins at the cell membrane. Because it connects the center of the muscle cell to the edge of the cell, the dystrophin protein is extremely long. ![]() The dystrophin protein transfers the force of muscle contraction from the inside of the muscle cell outward to the cell membrane. Individuals with BMD genetic mutations make dystrophin that is partially functional, which protects their muscles from degenerating as badly or as quickly as in DMD. 1ĭMD occurs because the mutated DMD gene fails to produce virtually any functional dystrophin. The majority of mutations of the dystrophin gene are deletions of one or more parts of it. The dystrophin gene is the largest gene yet identified in humans and is located in the short arm of the X chromosome, in the Xp21.2 locus (a locus is the position of a gene on a chromosome). In 1987, the protein associated with the DMD gene was identified and named dystrophin. Genes contain codes, or recipes, for proteins, which are important biological components in all forms of life. In 1986, MDA-supported researchers identified a gene on the X chromosome that, when flawed (mutated), causes Duchenne, Becker, and an intermediate form of muscular dystrophies. Until the 1980s, little was known about the cause of any of the forms of muscular dystrophy. Learn about MDA’s COVID-19 response Cause of DMD ![]()
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