Difference between revisions of "Emery-Dreifuss muscular dystrophy"
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Revision as of 13:09, 28 September 2007
|Emery-Dreifuss muscular dystrophy|
|OMIM||181350 604929 310300|
|DiseasesDB||31705 33543 31704|
Emery-Dreifuss muscular dystrophy is a condition that chiefly affects muscles used for movement (skeletal muscles) and heart (cardiac) muscle. Among the earliest features of this disorder are joint deformities called contractures, which restrict the movement of certain joints. Contractures become noticeable in early childhood and most often involve the elbows, ankles, and neck. Most affected individuals also experience slowly progressive muscle weakness and wasting, beginning in muscles of the upper arms and lower legs and progressing to muscles in the shoulders and hips.
Almost all people with Emery-Dreifuss muscular dystrophy have heart problems by adulthood. In many cases, these heart problems stem from abnormalities of the electrical signals that control the heartbeat (cardiac conduction defects) and abnormal heart rhythms (arrhythmias). If untreated, these abnormalities can lead to an unusually slow heartbeat (bradycardia), fainting (syncope), and an increased risk of stroke and sudden death.
The types of Emery-Dreifuss muscular dystrophy are distinguished by their pattern of inheritance: X-linked, autosomal dominant, and autosomal recessive. Although the three types have similar signs and symptoms, researchers believe that the features of autosomal dominant Emery-Dreifuss muscular dystrophy are more variable than the other types. A small percentage of people with the autosomal dominant form experience heart problems without any weakness or wasting of skeletal muscles.
X-linked Emery-Dreifuss muscular dystrophy is the most common form of this condition, affecting an estimated 1 in 100,000 people. The autosomal recessive type of this disorder appears to be very rare; only a few cases have been reported worldwide. The incidence of the autosomal dominant form is unknown.
Mutations in the EMD and LMNA genes cause Emery-Dreifuss muscular dystrophy. The EMD and LMNA genes provide instructions for making proteins that are components of the nuclear envelope, which surrounds the nucleus in cells. The nuclear envelope regulates the movement of molecules into and out of the nucleus, and researchers believe it may play a role in regulating the activity of certain genes.
Most cases of Emery-Dreifuss muscular dystrophy are caused by mutations in the EMD gene. This gene provides instructions for making a protein called emerin, which appears to be essential for the normal function of skeletal and cardiac muscle. Most EMD mutations prevent the production of any functional emerin. It remains unclear how a lack of this protein results in the signs and symptoms of Emery-Dreifuss muscular dystrophy.
Less commonly, Emery-Dreifuss muscular dystrophy results from mutations in the LMNA gene. This gene provides instructions for making two very similar proteins, lamin A and lamin C. Most of the LMNA mutations that cause this condition result in the production of an altered version of these proteins.