Emily and Cassandra
Duchenne muscular dystrophy

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Nature of the Genetic Difficulty

Duchenne muscular dystrophy is an X-linked recessive disorder, meaning that the mutation is carried on an X chromosome from a parent, and is transferred to their offspring in the form of a carrier gene, or the disease itself.
If a male is to be afflicted, he must only receive a mutated X-chromosome from his mother (because he is hemizygous for X). However, females have a significantly lower occurrence of the disease because for them, inheritance requires a copy of the gene mutation on each of their two X-chromosomes.

Basis Facts of Disease

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Symptoms of the disease may be visible in early infancy. More commonly, it is diagnosed around the age of five. Calf and deltoid muscles enlarge (pseudohypertrophy), fat and fibrotic tissue replace muscle tissue, and eventually the patient becomes wheelchair dependent. Over time, skeletal deformities may develop (namely, the curvature of the spine) and ultimately, paralysis will set in. Duchenne muscular dystrophy, unfortunately, is terminal.
Prenatal tests such as amniocentesis and chorion villus sampling can detect the disease after eleven weeks of pregnancy, and with a 95% rate of accuracy. Additionally, DNA tests and muscular biopsies can serve the same purpose once the infant is born.
Although there exists no cure for Duchenne muscular dystrophy, stem cell research is showing promising results in tests on genetically-altered mice. Non-jarring physical activity such as swimming is encouraged, as inactivity will worsen the progression of the disease.

Prognosis

Paralysis is certain. Respiratory failure, in almost all cases, results in the necessity of a ventilator. The disease is generally debilitating.
Most people afflicted with Duchenne muscular dystrophy die between the ages of fifteen and thirty. Some cases have been recorded of DMD patients living into their forties, but the terminal disease mostly takes its victims before they reach that age.

Sources Cited

http://www.mda.org/disease/dmd.html
http://www.genome.utah.edu/DMD/methods_abstract.shtml
http://www.eurekalert.org/pub_releases/2007-01/jhmi-cbp011907.php
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