A mutation in the dystrophin gene, located in humans on the X chromosome (Xp21) is the main cause for this disorder. The dystrophin gene stores the information which codes for the protein dystrophin, an important structural component within muscle tissue. Dystrophin is responsible for connecting the cytoskeleton of each muscle fibers to the underlying basal lamina (extracellular matrix) through a protein complex containing many subunits. It also acts as a shock absorber, provides structural stability to the dystroglycan complex (DGC), located on the cell membrane. The absence of dystrophin allows excess calcium to penetrate the sarcolemma (cell membrane). In a complex cascading process that involves several pathways and is not clearly understood, increased oxidative stress within the cell damages the sarcolemma, and eventually results in the death of the cell. Necrosis of muscle fibers occurs and are ultimately replaced with adipose and connective tissue.
A person afflicted with Duchenne muscular dystrophy (DMD) makes them to move little bit slower than the normal kids. Kids, usually boys are generally diagnosed with DMD between the ages from one and six. There are some noticeable symptoms,childrens with DMD usually have trouble jumping, running or hopping,they may fall down frequently and find it difficult for them to do activities like running, climbing the stairs and getting up from the sitting positions. If you notice a boy with DMD, they often stand up with a movement called Gower’s maneuver. A child with DMD tend to walk on their forefeet,because of an increased calf tonus. Besides, toe walking becomes compensatory adaptation to knee extensor weakness . These noticeable signs would certainly help a doctor to spot DMD early. Rapid progression of muscle degeneration simply means DMD process increases over the time. DMD causes more and more muscle weakness till the individual’s muscles die.The muscle do not necessarily get smaller. At times, the muscle cells turn into fat and scar tissue so the muscle can look big but not strong.
As the child with DMD grows up, the condition gets more serious. Walking and running can become more difficult as the disorder progresses. Kids with DMD will eventually need some help getting around. They need to hold on when they walk and eventually use an electrical wheel chair. They also tend to get fatigue more easily.
Clinical tests like DNA tests can be done to examine if any mutation occurs in the DNA sequence, followed by muscle biopsy where the muscle sample is taken from the affected individual and examined it microscopically. Prenatal test, however, also plays a significant role in the lab diagnosis for the DMD. This test is carried out if one or both parents are 'carriers' of DMD and is normally being conducted during pregnancy and find out if the fetus is affected with DMD. Other tests to diagnose DMD including an electromyography (EMG) which shows that weakness is caused by destruction of muscle tissue rather than by damage to nerve. A blood test can also be done by detecting the absence of the dystrophin.
There is still no cure for DMD till date but the treatment is improving over the time. Physical therapy can slow down its progress, and sooner the therapy begins, the more effective it will be. So early diagnosis of DMD is crucial. Scientists are constantlly working to develop the drugs that could alter the DNA’s sequence that codes the DMD. Recent stem-cell research is showing promising vectors that may replace damaged muscle tissue.
Reference :
http://en.wikipedia.org/wiki/Duchenne_muscular_dystrophy#Pathogenesis
http://en.wikipedia.org/wiki/Muscle_biopsy
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