Duchenne Muscular Dystrophy
Definition/History
It is the most fatal of all the muscular dystrophies; pseudohypertonic muscular dystrophy, widely known as Duchenne muscular dystrophy. Affecting only boys, Duchenne is a result of the absence of the protein dystrophin in muscle fibres. This absence causes muscles to weaken and wither away.
In the 1850s and 1860s, a French doctor by the name of Guillaume-Benjamin-Amant Duchenne observed patients with the signs and symptoms of muscular dystrophy. However, Duchenne did not believe that the problem was within the muscles themselves, but of a nervous system disorder because of the mental retardation of some of his patients. (Muscular dystrophy was not know known to be a muscular disease until a German doctor named Ernst Leyden noticed that the symptoms were much different than those of obvious nervous system problems.)
Duchenne’s research was done with a harpoon-like device called a “trochar”, which he invented himself. It is a hollow needle that was to be pushed through the skin into the muscle. The needle would then be taken out, extracting bits of muscle in the process. This today is known as a muscle biopsy.
Causes
Duchenne is a disease, which can only be inherited. The mother is usually the one who carries a defective gene, since males with Duchenne rarely become fathers. This occurrence protects females from inheriting the defective gene. The chance of a boy receiving the X chromosome with the defective gene is fifty percent.
The gene that causes Duchenne muscular dystrophy is ten times larger than any human gene found to this day and five hundred times larger than the average size gene. Because of its large size, it is more susceptible to damage. People who have the disease have large sections of it missing or alterations in the gene.
Dystrophin, the protein found in normal muscle fibres, is absent within the muscles of a child suffering from DMD. Without dystrophin, the outer membrane of a muscle cell will begin to leak. This may begin the buildup of electrically charged calcium particles that enter through the leaky membrane. It is probable that this calcium buildup activates a protein that dissolves muscle fibres.
Effects/Symptoms
The first signs of DMD may begin in the womb, but are usually manifested between the ages of one and three years old. Typically, by the time a boy is able to walk he will have an abnormal waddling gait. He will have trouble getting up and climbing stairs. As he becomes older, his posture will change, with an arched back, and stomach thrusting forward. This position actually allows for balance among the weakened muscles.
The first muscles to be affected are in the upper arms and legs, and hips. Those muscles shrink in size, but oddly enough, the calf muscles will enlarge. The reason for this enlargement is due to the replacement of the dying muscle fibres with fat and connective tissues. By the age of ten (or, in some cases, a couple of years earlier) a boy with Duchenne will be confined to a wheelchair. His joints in the ankles and elbows will pull into awkward positions dues to the shortening of the muscles in the arms and legs.
As the boy reaches his late teens his lung muscles will become affected leading to difficulty in breathing and the development of lung infections, which are the number one cause of death among DMD sufferers. Occasionally, the heart muscle is affected and heart failure follows.
Diagnosis
The initial diagnosis of Duchenne is a simple one. The doctor will learn which muscles were primarily affected, the age of onset of the symptoms, and the severity of those symptoms.
The second step is the electromyography. This monitors the muscle’s electrical activity at rest and during contraction. Small needlelike electrodes are inserted through the skin into selected muscles. When the muscle contracts it shows a sharp decrease in electrical response followed immediately by an increase. The electromyography of a dystrophic muscle is very distinctive. There are many brief muscle contractions and there is little or no time spent in rest.
After the electromyography, a doctor will perform a muscle biopsy. A muscle biopsy is the removal and examination of a small piece of muscle. A muscle affected by DMD will show shrunken cells and the expansion of fatty tissues.
The last test is for the protein dystrophin. As stated before, if there is no dystrophin found in the muscle fibres that person would have Duchenne.
Treatment
As of yet, there is no cure for any type of muscular dystrophy. However, treatment does exist.
Physical therapy, exercise, and surgery are all candidates for treatment. The exercise and physical therapy keep the muscle fibres as fit as possible. For children with DMD, swimming is a common exercise. The water provides support and exercises important voluntary muscles in the process.
Surgery corrects what exercise and physical therapy cannot. When the shortening of muscles occur, surgery is used to correct the pull on an ankle or elbow.
Future Outlook/Research
Of all the muscular dystrophies, Duchenne is the one that researchers concentrate on the most. Because of its fatal nature, scientists need to know more about it. They have already pinpointed the gene responsible for the disease, now they just need to know what they can do to fix this defect.
Some researches are attempting to decipher the chemical role of dystrophin, while others concentrate on the growth of new muscles or injections of copies of the defective gene into the muscles, which are called myoblasts. The myoblasts fuse with a damaged cell creating a healthy, new cell.
Like many other inherited diseases, some scientists believe that the cure lies within the insertion of a healthy gene, or gene therapy. Nevertheless, like many of the other methods, gene therapy is not a practical method for curing Duchenne Muscular Dystrophy.