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Emery-Dreifuss muscular dystrophy
Emery-Dreifuss muscular dystrophy is a condition primarily affecting skeletal and cardiac muscles, characterized by early-onset joint contractures, progressive muscle weakness, and significant heart problems.
Overview
Emery-Dreifuss muscular dystrophy is a condition that primarily affects muscles used for movement (skeletal muscles) and the heart (cardiac muscle). Among the earliest features of this disorder are joint deformities called contractures. Contractures restrict the movement of certain joints, most often the elbows, ankles, and neck, and usually become noticeable in early childhood. Most affected individuals also experience muscle weakness and that worsen slowly over time, beginning in muscles of the upper arms and lower legs and later also affecting muscles in the shoulders and hips.
Almost all people with Emery-Dreifuss muscular dystrophy develop heart problems by adulthood. In many cases, these heart problems are abnormalities of the electrical signals that control the heartbeat (cardiac conduction defects) and abnormal heart rhythms (arrhythmias). If untreated, these abnormalities can lead to a sensation of fluttering or pounding in the chest (palpitations), an unusually slow heartbeat (bradycardia), fainting (syncope), heart failure, and an increased risk of sudden death.
Researchers have identified several types of Emery-Dreifuss muscular dystrophy that are distinguished by their pattern of inheritance: X-linked, autosomal dominant, and autosomal recessive. The types usually have similar signs and symptoms, although a small percentage of people with the autosomal dominant form experience heart problems without any weakness or wasting of skeletal muscles.
Frequency
The overall prevalence of Emery-Dreifuss muscular dystrophy is unknown. The X-linked type of this disorder affects an estimated 1 in 100,000 people. The prevalence of the autosomal dominant type is unknown, although it appears to be more common than the X-linked type. The autosomal recessive type appears to be very rare; only a few cases have been reported worldwide.
Causes
Mutations in several genes, including EMD, FHL1, and LMNA, can cause Emery-Dreifuss muscular dystrophy. Mutations in the EMD gene or, less commonly, in the FHL1 gene cause the X-linked type of the condition. Mutations in the LMNA gene cause both the autosomal dominant and autosomal recessive types of the condition.
The genes associated with Emery-Dreifuss muscular dystrophy appear to be essential for the normal function of skeletal and cardiac muscle. 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. The protein produced from the FHL1 gene appears to be involved in other muscle cell functions, including chemical signaling, maintaining the structure of these cells, and influencing muscle growth and size.
Mutations in the EMD, FHL1, and LMNA genes that cause Emery-Dreifuss muscular dystrophy prevent the production of their respective proteins or lead to abnormal or nonfunctional versions of these proteins. Researchers speculate that changes in EMD or LMNA could weaken the structure of the nuclear envelope in cells that undergo a lot of mechanical stress, such as skeletal and cardiac