What happens in Duchenne muscular dystrophy, exactly?

What is it?

Duchenne muscular dystrophy (DMD) is a genetic disease that leads to muscle loss. The first symptom, muscle weakness, typically starts around the age of four and gets worse quickly. The average life expectancy is 26 years. DMD is much more common in males than in females, and it affects about 1 in 3600 male infants.

What causes it?

DMD is caused by a faulty gene in the X chromosome. This is why it is so much more common in men than in women – the sex chromosomes of men are XY, while those of women are XX. Men get only one X chromosome, so anything on it will be manifested. Women get two, so the genes on them balance each other our and in the case of DMD the healthy gene can compensate for the dysfunction of the faulty gene.

What happens during it?

Muscle cells have a internal skeleton consisting of proteins. They are also surrounded by a protein mesh called the extracellular matrix. The gene that is mutated in DMD, the dystrophin gene, is supposed to produce a protein that connects these two. It penetrates the cell membrane while doing this, and it plays an important role in keeping the cell membrane stable and functioning.

If the dystrophin protein is missing as it is in DMD, too much calcium starts to leak inside the cell. The controlled movement of calcium is very important in processes like muscle contraction, and this alters the required intricate balance. This eventually leads to too much water entering the mitochondria – the cell organelles that release energy for the cell to use – and they burst.

The dysfunction of mitochondria causes an increased production of reactive molecules. Reactive molecules are dangerous to the cell because they will essentially react with anything that comes their way, and if this kind of reactive molecule takes a, say, hydrogen, from some other molecule, that molecule might not be able to function anymore. These reactive molecules damage the cell membrane to such an extent that the cell dies.

Our body is quite good at recovering after damage, but the regeneration of cells gets a lot harder when the damaged cells were highly specialized. This is the case with neurons, and also muscle cells. When the muscles start to recover after the cell deaths, the lost cells aren’t replaced with new muscle cells, but fat cells and other connective tissue. These new cells obviously don’t have the ability to contract, and when enough of this has happened within a muscle, it loses its ability to function.

How can it be treated?

There is no cure for DMD. Good care can, however, significantly improve the quality of life of the affected and help them live longer. Some medications, light exercise and physical therapy are useful.  In the later stages of the disease the muscles needed for respiration start to lose their ability to function, and it becomes necessary to use some form of respiration assistance.

 

 

 

Sources: en.wikipedia.org/wiki/Duchenne_muscular_dystrophy, https://en.wikipedia.org/wiki/Sarcolemma, https://en.wikipedia.org/wiki/Dystrophin, https://en.wikipedia.org/wiki/Extracellular_matrix, http://emedicine.medscape.com/article/1259041-overview#a9

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