Duchenne Muscular Dystrophy Genetics

Duchenne muscular dystrophy is a hereditary disease that generally affects males. One in 3500 makes has this disease. The manifestation of this disease is similar to that of the other muscular dystrophy where there is a progressive degeneration of muscles. Most individuals suffering from it die by the time they are 25. This disease is caused due to a mutation in the gene called dystrophin.

What is Duchenne Muscular Dystrophy?

To understand this condition you must know what is muscular dystrophy, information for which is available on Buzzle. This disease is a fatal X linked recessive disorder. It is characterized by a progressive muscular atrophy that gradually leads to loss of movement and then death. The disease symptoms usually begin to show at the age of 5. Initially there is a muscular weakness in the proximal part of the limbs. There is a considerable loss of muscle at this stage. There is also a swelling at some stage known as pseudohypertrophy of muscles where the calf and deltoid muscles swell. By adolescence individuals suffering from this disorder have to rely upon a wheelchair. The progression of degeneration is quite rapid lead and the cause of death is usually due to the failure of respiratory muscles. The life expectancy is around 20 to 25 years due to the progression of the disease and limited treatment options.

Inheritance and Genetics of Duchenne Muscular Dystrophy

This medical condition is a genetic disorder caused due to a mutation in the dystrophin gene present on the X chromosome. The mutation is most often due to inheritance and sometimes due to spontaneous germline transmission. The locus of mutation for this disorder on the dystrophin gene is Xp21. The reason for it being seen more in men is due to the single copy of X chromosome in males. Women will only have this disorder when present in both the X chromosomes, which is quite rare. Females are therefore carriers of the mutation and can transfer this mutation to the son, who will be afflicted by the disorder. Females usually show mild form of the disease which is not fatal.

The following table will give you the chances of transfer possible from a parent to an offspring.

Transfer of Mutation	Inheritance Odds
Mother to Daughter	0 % disease, 50% carrier, 50% no carrier
Father to Daughter	0% disease, 100% chance of daughter being the carrier
Mother to Son	50% disease, 50% no disease (males cannot be carriers)
Father to Son	0% chance as father can pass on Y linked traits and not X

The Dystrophin Gene

The gene dystrophin codes for a protein called dystrophin that provides support to the muscles of the body. It strengthens the muscles by providing anchorage to the internal cytoskeleton to the surface membrane. In the absence of dystrophin the cell membrane becomes extremely permeable which leads to drastic changes in pressure causing cell death. Once a cell dies an immune response may be triggered that can worsen the fate of the already damaged tissue. Thus if this gene is mutated the protein dystrophin won't be synthesized or may not be completely functional leading to progressive muscle damage. Thus this disease is not that complex but its consequences are always fatal in males. The symptoms of this disease are similar to muscular dystrophy symptoms, the only difference is the point or locus of mutation in the gene.

There is no cure for this disease however gene therapy that is able to reverse mutation is the ray of hope that scientists all over the world are working on. If you do know someone afflicted by this disease remember that making the individual comfortable and taking utmost care of their needs is very important.