The gene that makes the dystrophin protein is found on the X chromosome. Problems with the dystrophin protein are caused by changes, known as mutations, to the dystrophin gene. These include:
Large missing pieces of the gene (called deletions)
Large doubled pieces of the gene (called duplications)
Small missing or extra pieces of the gene
Tiny substitutions (switched pieces of information) in the gene
Some types of mutations in specific areas of the dystrophin gene cause Duchenne muscular dystrophy and other types of mutations cause Becker muscular dystrophy. In most cases, after genetic testing has been done it is possible to tell whether a particular mutation causes Duchenne muscular dystrophy or if it causes Becker muscular dystrophy. The lab can tell this based on the type and location of the mutation in the dystrophin gene. In some cases, the mutation in a family causes symptoms that fall between those seen in Duchenne and Becker muscular dystrophy. Everyone in the same family who is affected with Duchenne or Becker muscular dystrophy almost always has the same mutation in the dystrophin gene.
Duchenne and Becker muscular dystrophy are X-linked conditions, meaning that the gene for dystrophin is found on the X chromosome. Males have one copy of the X chromosome and one copy of the Y chromosome. Females have two copies of the X chromosome. The difference in the number of X chromosomes explains why Duchenne and Becker muscular dystrophy are most often seen in males. Because males have only one copy of the X chromosome, a mutation in the dystrophin gene may cause a lack of working dystrophin protein.
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