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Mytonic Muscular Dystrophy

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Myotonic Muscular Dystrophy (MMD) is a disease genetically based and inherited from one generation to the next. Such disease is also known as dystrophia mytonica and SteinertÐŽ¦s disease. This genetic defect was an unusual one that ascended from the unknown and shook the scientific community in the early 1990s. Unlike other types of dystrophy, MMD often doesnÐŽ¦t appear to be a problem until adulthood and is characterized by myotonia, a delayed relaxation of the muscles after contraction. It is a form of dystrophy that affects the muscle and numerous organs in our body, while the symptoms widely vary from one person to next. Overall, MMD is a rare disease found in 1 of 8,000 in which ultimately affects 40,000 people throughout the United States.

Myotonic Dystrophy is a multisystem disorder that affects skeletal muscle, smooth muscle, eyes, heart, endocrine system, and central nervous system. It can be classified into two types: DM1 and DM2, also known as Proximal Myotonic Myopathia (PROMM). DM1 is caused by a continuous repeat of CTG located on chromosome 19, while DM2 is caused by the expanded quadruplet of CCTG on chromosome 3. They are both inherited as autosomal dominant trait, differing only by the characteristic of DM2 that contains one or more ion-channel defects. The second type of myotonic dystrophy is rarely found; therefore I will focus my research mainly on type 1. Here, clinical findings have been categorized into three phenotypes: congenital, classical, and mild. In congenital MMD, onset occurs in infancy or early childhood of less then 10 years of age. During infancy, the disease may be characterized by hyponia with sucking and swallowing, and severe generalized weakness at birth, often with respiratory deficiency and early death. Myotonia most often begins in early childhood generally between the ages of five and ten years of age. Muscle weakness, wasting of the face, and distal limbs are the common characteristics; while absence of tendon reflexes, club foot, and mental retardation are also common. In classical MMD, onset occurs between the ages of ten and fifty years. This is the most common among the patients and is characterized with symptoms of weakness (especially of the distal limb, masticatory, and facial muscles), myotonia (often demonstrated by the inability to quickly release a hand grip), and cataracts in the lens of the eyes. Last but not least is the mild MMD with an onset after fifty years of age. It is characterized by cortical cataracts which require slit lamp examination for early detection and mild mytonia. Other symptoms may be respiratory and cardiac abnormalities, gastrointestinal problems, excessive sleepiness, hormonal irregularities, relative insensibility to insulin, and even a personality frequently described as apathetic, unconcerned, or lacking in emotion. The MMD disease certainly runs in the family. Thus, if one parent possesses the disorder, then every child of that person will have a 50% chance of inheriting the genes that caused it. Unfortunately, the disease inherited by the next generation may be more severe with an earlier onset than that of the parent.

In the year 1992, the astounding genetic discovery of MMD was made by three teams of scientists. In people with MMD, they came across a region of DNA on chromosome 19 thatÐŽ¦s larger than its normal size. The expanded area of DNA is located in a gene that transfers information for a protein known as myotonic protein

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