If one or both of your parents has a mutated gene that causes muscular dystrophy , the condition may be passed on to you. Although most forms of muscular dystrophy are caused by a mutation on the X chromosome influencing production of a protein called dystrophin — a protein needed to build and repair muscles — the different types of the condition each have their own set of unique genetic mutations.
Occasionally, the genetic mutation that causes muscular dystrophy can develop as a new event in a family. This is known as a spontaneous mutation. This means you will be diagnosed with the condition at some point.
In general, if both you and your partner have a genetic mutation that causes recessive inherited muscular dystrophy, then your child has a 1 in 4 chance for each of the following:. On the other hand, a dominant inherited disorder means you only need to inherit a genetic mutation from one parent to be affected.
Myotonic dystrophy, facioscapulohumeral muscular dystrophy, oculopharyngeal muscular dystrophy, and some types of limb-girdle muscular dystrophy are passed along this way. Meanwhile, a sex-linked disorder is caused by a mutation in a gene on the X chromosome. Males have one X and one Y sex chromosome, while females have two X chromosomes. Males have only one copy of each gene on the X chromosome. Finally, spontaneous gene mutations — in which genes mutate for no apparent reason, regardless of parental DNA — can sometimes cause muscular dystrophy.
This means the condition can develop in people with no family history of it. However, a child with no family history also can be affected with muscular dystrophy when the condition is recessive. The two conditions differ in their severity, age of onset, and rate of progression. In boys with Duchenne muscular dystrophy, muscle weakness tends to appear in early childhood and worsen rapidly. Affected children may have delayed motor skills, such as sitting, standing, and walking.
They are usually wheelchair-dependent by adolescence. The signs and symptoms of Becker muscular dystrophy are usually milder and more varied. In most cases, muscle weakness becomes apparent later in childhood or in adolescence and worsens at a much slower rate. Both the Duchenne and Becker forms of muscular dystrophy are associated with a heart condition called cardiomyopathy.
This form of heart disease weakens the cardiac muscle, preventing the heart from pumping blood efficiently. In both Duchenne and Becker muscular dystrophy, cardiomyopathy typically begins in adolescence. Later, the heart muscle becomes enlarged, and the heart problems develop into a condition known as dilated cardiomyopathy. Signs and symptoms of dilated cardiomyopathy can include an irregular heartbeat arrhythmia , shortness of breath, extreme tiredness fatigue , and swelling of the legs and feet.
These heart problems worsen rapidly and become life-threatening in most cases. Males with Duchenne muscular dystrophy typically live into their twenties, while males with Becker muscular dystrophy can survive into their forties or beyond. A related condition called X-linked dilated cardiomyopathy is a form of heart disease caused by mutations in the same gene as Duchenne and Becker muscular dystrophy, and it is sometimes classified as subclinical Becker muscular dystrophy.
People with X-linked dilated cardiomyopathy typically do not have any skeletal muscle weakness or wasting, although they may have subtle changes in their skeletal muscle cells that are detectable through laboratory testing.
Duchenne and Becker muscular dystrophies together affect 1 in 3, to 5, newborn males worldwide. A clinical diagnosis may be made when a boy has progressive symmetrical muscle weakness. The symptoms present before age 5 years, and they often have extremely elevated creatine kinase blood levels which are described below.
If untreated, the affected boys become wheelchair dependent before age 13 years. A muscle biopsy taking a sample of muscle for dystrophin studies can be done to look for abnormal levels of dystrophin in the muscle. The dystrophin protein can be visualized by staining the muscle sample with a special dye that allows you to see the dystrophin protein.
A muscle which has average amounts of dystrophin will appear with the staining technique as though there is caulking around the individual muscles cells and it is holding them together like window panes. A boy with Duchenne, on the other hand, will have an absence of dystrophin and appear to have an absence of the caulking around the muscle cells. Some individuals can be found to have an intermediate amount of the dystrophin protein.
Often these boys are classified as having Becker muscular dystrophy. Genetic testing looking at the body's genetic instructions on a blood sample for changes in the DMD gene can help establish the diagnosis of Duchenne muscular dystrophy without performing a muscle biopsy. Those individuals who are not found to have a detected change in the DMD gene using this method, and who are diagnosed with DMD by biopsy, still have a change in their gene but it is in areas of the gene that are not examined using these methods.
However, the results of genetic testing may not be conclusive of a diagnosis of DMD, and only the muscle biopsy can tell the level of dystrophin protein for sure. For the remaining individuals, a combination of clinical findings, family history, blood creatine kinase concentration and muscle biopsy with dystrophin studies confirms the diagnosis. Creatine kinase is an enzyme that is present normally in high concentrations in the muscle cells of our body. During the process of muscle degeneration or breakdown, the muscle cells are broken open and their contents find their way to the bloodstream.
Therefore elevated levels of creatine kinase can be detected from a blood test and it is a measure of muscle damage.
Elevated levels can be the result of multiple reasons including acute muscle injury, or chronic condition such as Duchenne muscular dystrophy. Treatment for Duchenne muscular dystrophy is aimed at the symptoms.
Aggressive management of dilated cardiomyopathy with anti-congestive medications is used, including cardiac transplantation in severe cases. Assistive devices for respiratory complications may be needed, especially at night. Because the mutation for Duchenne is found on the X chromosome, only females can be carriers for the mutation on the gene that encodes for dystrophin protein.
Carriers have an increased chance of having sons with Duchenne and daughters who are carriers. Carriers can have some symptoms of Duchenne, such as muscle weakness and cardiomyopathy. Though it is rare, some females can have the classic symptoms of Duchenne, and they are known as manifesting carriers.
All carriers should be evaluated by a healthcare provider familiar with Duchenne. It is important to remember that Duchenne is not always inherited from a carrier mother.
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