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Monday, July 30, 2012

CIRM Stem Cell Research Updates: Patient advocates speak in support of disease team...

Duchenne Advocates Voices herd!

CIRM Stem Cell Research Updates: Patient advocates speak in support of disease team...: Huntington's disease advocates speaking to the Governing Board Yesterday’s governing board meeting should have been a happy one. The age...

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What Is Duchenne Muscular Dystrophy?

Duchenne muscular dystrophy (DMD) is a severe recessive X-linked form of muscular dystrophy characterized by rapid progression of muscle degeneration, eventually leading to loss of ambulation and death. This affliction affects one in 3500 males, making it the most prevalent of muscular dystrophies. In general, only males are afflicted, though females can be carriers. Females may be afflicted if the father is afflicted and the mother is also a carrier/ affected. The disorder is caused by a mutation in the dystrophin gene, located in humans on the X chromosome (Xp21). The dystrophin gene codes for the protein dystrophin, an important structural component within muscle tissue. Dystrophin provides structural stability to the dystroglycan complex (DGC), located on the cell membrane.
Symptoms usually appear in male children before age 5 and may be visible in early infancy. Progressive proximal muscle weakness of the legs and pelvis associated with a loss of muscle mass is observed first. Eventually this weakness spreads to the arms, neck, and other areas. Early signs may include pseudohypertrophy (enlargement of calf and deltoid muscles), low endurance, and difficulties in standing unaided or inability to ascend staircases. As the condition progresses, muscle tissue experiences wasting and is eventually replaced by fat and fibrotic tissue (fibrosis). By age 10, braces may be required to aid in walking but most patients are wheelchair dependent by age 12. Later symptoms may include abnormal bone development that lead to skeletal deformities, including curvature of the spine. Due to progressive deterioration of muscle, loss of movement occurs eventually leading to paralysis. Intellectual impairment may or may not be present but if present, does not progressively worsen as the child ages. The average life expectancy for patients afflicted with DMD varies from late teens to early to mid 20s. There have been reports of a few DMD patients surviving to the age of 40, but this is extremely rare

What test are done to know if my son has DMD?

DNA test
The muscle-specific isoform of the dystrophin gene is composed of 79 exons, and DNA testing and analysis can usually identify the specific type of mutation of the exon or exons that are affected. DNA testing confirms the diagnosis in most cases.
Muscle biopsy
If DNA testing fails to find the mutation, a muscle biopsy test may be performed. A small sample of muscle tissue is extracted (usually with a scalpel instead of a needle) and a dye is applied that reveals the presence of dystrophin. Complete absence of the protein indicates the condition.
Over the past several years DNA tests have been developed that detect more of the many mutations that cause the condition, and muscle biopsy is not required as often to confirm the presence of Duchenne's.
Prenatal tests
If one or both parents are 'carriers' of a particular condition there is a risk that their unborn child will be affected by that condition. 'Prenatal tests' are carried out during pregnancy, to try to find out if the fetus (unborn child) is affected. The tests are only available for some neuromuscular disorders. Different types of prenatal tests can be carried out after about 11 weeks of pregnancy. Chorion villus sampling (CVS) can be done at 11–14 weeks, and amniocentesis after 15 weeks, while fetal blood sampling can be done at about 18 weeks. Women and/or couples need to consider carefully which test to have and to discuss this with their genetic counselor. Earlier testing would allow early termination, but it carries a slightly higher risk of miscarriage than later testing (about 2%, as opposed to 0.5%).