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Function of the Dystrophia Myotonica Gene
When functioning correctly, the dystrophia myotonica gene, located on chromosome 19, provides the body with myotonic dystrophy protein kinase (DMPK), essential for the continued normal activity of the heart, brain and muscular system. In addition, it may have a number of other functions, as yet undetermined. However, geneticists believe that the protein also has a strong connection to cellular communication.
The DMPK protein also inhibits the muscle protein myosin phosphate, a subunit of which is responsible for muscle contraction and relaxation - PPP1R12A.
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Mutations of the DMPK Gene
Within the dystrophia myotonica gene, a certain section contains a repeating sequence of nucleotides. Known as a trinucleotide repeat, it signifies three building blocks of DNA. The triplet cytosine-thyamine-guanine (CTG) in this particular gene repeats anywhere from five to 35 times. Occasionally, this repeat mutates abnormally and the sequence of CTG expands to a repeat of 50 to 5,000 times. This causes an altered version of messenger RNA to be created, impacting the normal production of the myotonic dystrophy protein kinase. Essentially, clumps of proteins become impacted within the cell, blocking the production of other proteins. Ultimately, the lack of protein production leads to a failure of the muscle cells to function properly, a condition known as type 1 myotonic dystrophy (DM1). Additional forms of myotonic dystrophy exist in name only; these are not associated with the dystrophia myotonica protein kinase and are caused by mutations on other chromosomes.
The different levels of repeated CTG sequences determine the severity of the disease. Adults with repeats numbering 35 to 49 are most likely at low risk, however, children may suffer problems in the future. Muscle wasting and weakness begins with 100 to 1,000 CTG repeats, while severe conditions that threaten one's life begin at 2,000 repeats.
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Symptoms, Diagnosis and Treatment of DM1
The health effects of dystrophia myotonica disorders present themselves in a variety of ways. Most commonly, patients suffering from the disorder exhibit muscle pain, fatigue and stiffness. Those suffering from type 1 often have additional pain in the face and jaw muscles, hands and may have drooping of the eyelids. Additional symptoms such as daytime sleepiness, muscle wasting, and respiratory problems can also occur.
The challenge with diagnosing myotonic dystrophy is the fact that it is just one of many muscular disorders that can develop in the human body. Prenatal genetic testing of chromosome 19 can identify problems before birth. Later in life, testing can also occur, but it is usually conducted after more likely causes are addressed.
Unfortunately for those afflicted, there is no cure for dystrophia myotonica disorders. Doctors are able to address some of the symptoms such as sleepiness and pain with various medications. Additionally, aerobic exercise and strength training can have strong benefits. Research has been conducted into antisense therapy, used to target DM1. Further studies and investigations are addressed every other year at the International Myotonic Dystrophy Consortium meeting.
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Muscle Tissue. (Supplied by the U.S. Federal Government; Public Domain; http://upload.wikimedia.org/wikipedia/commons/1/1b/Illu_muscle_tissues.jpg)