What Is Muscular Dystrophy?
Muscular dystrophy is a disease that causes the degeneration and necrosis of skeletal muscle fibers, which results in muscle weakness. By the way, necrosis means cell death, if you didn't know.
After the death of the cell eventually pseudohypertrophy sets in, which is the replacement of muscle with fat and connective tissue.
Pseudohypertrophy is very common in the calf's of someone with muscular dystrophy. There is a feeling of fat and connective tissue in case of pseudohypertrophy, which eventually causes the muscle to look big, yet it is really very weak.
It is important to remember that muscular dystrophy does not involve the nervous system. Rather muscular dystrophy is the result of a genetic mutation of the dystrophin gene, which is found in the X-chromosome.
Types Of Muscular Dystrophy
The two most common types of muscular dystrophy are Duchenne Muscular Dystrophy (DMD) and Becker Muscular Dystrophy (BMD)
DMD is the total absence of the dystrophin gene. This is a mutation of the dystrophin gene in the total absence of dystrophin. This disease is more common in males than in females and becomes evident around the ages of two to three years old.
This type of muscular dystrophy is the most common and most severe of the muscular dystrophies.
BMD still has muscular degeneration, but it is not nearly as severe, because this mutation deals with deform dystrophin. However, it still leads to many muscular problems.
As I mentioned before, this disease ultimately comes down to a mutation of the dystrophin gene, which is found in the X chromosomes.
Males have an X and a Y chromosome. That means if there is a mutation of their X chromosome then they're out of luck. This is why one out of every 3500 males deal with DMD muscular dystrophy.
Girls, on the other hand, are lucky because they have two X chromosomes. So, they tend to be asymptomatic. If one of that X-chromosomes becomes mutated, the other chromosome can compensate for it.
BMD is the most common muscular dystrophy in females and it's much less severe than DMD.
Both DMD and BMD deal with a problem of dystrophin. Here is our healthy cell muscular membrane that has dystrophin. There are some important labels that like sarcolemma, B-Dystroglycan, F-actin. But the most important one that i want to point out is Dystrophin.
Dystrophin is a large protein that attaches portions of the sarcomere to the cell membrane.
Think of house. A house needs to have support beams to give it structure and support. If there aren't support beams then the house is more susceptible to collapse.
Dystrophin is the support beam to the muscle cell. it is connected to the actin and attaches to the protein B-Dystroglycan, which is embedded into the sarcolemma. This protein then attaches to connective tissue. All together this allows the forces generated by the sarcomere shortening to be effectively transmitted to the entire muscle. Without Dystrophin these forces are not effectively transmitted resulting in muscle weakness.
If a person doesn't have Dystrophin or has a defective one, the muscle cell is weak and loses the necessary support to prevent damage, For this reason, those with DMD easily damaged the sarcomas of their muscle cells. Damage to the sarcolemma causes the cell to become leaky.
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An important enzyme creatine kinase inside the muscle cells is leaked out into the extracellular fluid, which it then enters into the blood.
Elevated levels of creatine kinase in the blood is a sign that muscle cells are being damaged. After a myocardial infarction or damage to muscles by certain drugs called statins there will be elevated creatine kinase levels in the blood. Measuring the levels of this enzyme is a an important diagnostic test for MD.
Boys with DMD are usually asymptomatic at birth until the ages of two to three. This is when the postural muscles of the hips and shoulders begin to be affected along with pseudohypertrophy of the calves.
Scoliosis is very common in those who have DMD, because of an imbalance between the agonist and antagonistic muscles that support the spine due to the degeneration of those muscles.
Most people with DMD are in a wheelchair between the ages of 7 to 12.
Now that we all understand that muscular dystrophy deals with muscle this leads us to the fatality of this disease.
Main Muscles In Relation To DMD
We have muscles that help us breathe. Our respiratory muscles are the important part of helping us breeze. We have the diaphragm in our internal and external intercostal muscles.
A weakness of the respiratory muscles leads to an ineffective cough, frequent respiratory infections and decreasing respiratory reserve.
The other important muscles that help us are our cardiac muscles. They allow our heart to contract cardiomyopathy, which is very common with DMD. Cardiomyopathy develops as the cardiomyocytes die.
Death from respiratory and cardiac muscle involvement usually occurs in young adulthood. This is the cause of death for people with DMD, their life expectancy is shortened and death usually occurs in young adulthood around the age of 30.
However, due to advances in treatment, some have lived to be in their 40s and 50s. But that still is pretty rare.
Testing For MD
The initial signs of DMD are often seen and observing a child, especially in how they move. They often have difficulty climbing stairs and will begin to struggle to support themselves while standing.
Blood samples can also be taken where levels of creatine kinase can be checked. This enzyme being elevated in the blood is a sign of muscle damage and is seen in those with MD.
Two-thirds of MD cases are inherited. Checking family history can also indicate if a child is at risk.
Medical advances are helping people with DMD live stronger and better lives for a longer period of time. There are many experimental drugs that are helping slow down the degeneration of muscle.
Therapy can be used to help the muscles stay stronger for a longer period of time.
Corticosteroids can be used to help with inflammation and improve muscle regeneration. They have shown to also slow the decline in muscle strength with those with MD.
There have also been recent breakthroughs using anti-mouse statin and follistatin have that show a promotion of growth and the slowing down of the degeneration of muscles. Research is ongoing and treatments are improving the life expectancy of those with this debilitating disease.