Emery-Dreifuss muscular dystrophy (EDMD) is one of nine types of muscular dystrophy, a group of genetic, degenerative diseases primarily affecting voluntary muscles. It is named after Alan Emery and Fritz Dreifuss, physicians who first described the disorder in a Virginia family in the 1960s. EDMD is a relatively benign form of dystrophy, with onset in early childhood and thereafter relatively slow progression that is characterized by the triad:
- Early contractures, often before there is any significant weakness, of elbows, Achilles tendons, and post-cervical muscles (with subsequent limitation of neck flexion, but later forward flexion of the entire spine becomes limited)
- Slowly progressive muscle wasting and weakness with a distinctive humero-peroneal distribution (i.e. proximal in the upper limbs and distal in the lower limbs) early in the course of the disease. However, weakness later extends to the proximal limb girdle musculature. Weakness is rarely profound
- Cardiac conduction defects (ranging from sinus bradycardia, prolongation of the PR interval on electrocardiography to complete heart block). A generalized cardiomyopathy may also supervene. Thus, affected individuals may die suddenly from heart block, or develop progressive cardiac failure. The latter may occur subsequent to the insertion of a pacemaker to correct an arrhythmia.
Mutations in the EMD and LMNA genes cause Emery-Dreifuss muscular dystrophy. These 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. EMD gene provides instructions for making a protein called emerin, which is important for normal skeletal and heart muscle function. LMNA gene provides instructions for making two very similar proteins, lamin A and lamin C.
In most cases, EDMD is inherited as an X-linked or autosomal dominant disease. In extremely rare cases, autosomal recessive inheritance has been reported.
- X-linked (caused by a mutation in the EMD gene): If the mother is affected and the father is not, then the male offspring is affected and the female offspring are carriers. X-linked is the most common form, affecting an estimated 1 per 100,000 individuals
- Autosomal dominant (caused by a mutation in the LMNA gene): 76% of the individuals affected by Emery-Dreifuss Muscular Dystrophy acquire a new mutation in this LMNA gene with no history of the disorder in the family. There are varied case reports that exist for autosomal dominant Emery-Dreifuss Muscular Dystrophy. The current prevalence is unknown
- Autosomal recessive type: Both parents must either be carriers or be affected in order for the child to be affected. Autosomal recessive is the rarest of the three types. There are very few cases worldwide.
The overall prevalence of EDMD is unknown. The X-linked form is estimated to affect 1 in 100,000 people in the general population. EDMD is believed to be the third most common form of muscular dystrophy. X-linked EDMD is fully expressed in males only. Approximately 10-20 percent of female carriers for X-linked EDMD will develop heart conduction defects and/or muscle weakness. The autosomal dominant and recessive forms of EDMD affect males and females in equal numbers.
Diagnosis relies on recognition of the clinical triad (although the cardiac manifestations may be absent at onset). Muscular imagining may reveal the isolated involvement of the soleus, suggestive of the initial stages of the disease. For X-linked forms linked to the EMD gene, immunodetection of emerin in various tissues (muscle, lymphoblasts, skin) reveals an absence or reduction of the protein. The diagnosis can be confirmed by detection of EMD mutations. For autosomal forms and X-linked forms linked to FHL1, molecular analysis of LMNA, FHL1, and TMEM43 is the only approach for confirming the diagnosis. Genetic testing and prenatal diagnosis for X-linked Emery-Dreifuss muscular dystrophy are available on a clinical basis.
Treatment is a management of manifestations as they appear. Stretching and working with a physical therapist is useful in preventing or delaying contractures. Occupational therapy can help patients adapt their activities and environment to their own particular needs. Ankle and foot braces are used to prevent leg deformity. Surgery may be necessary to release contractures. Exercise can help maintain muscle use and overall good health. Affected individuals may eventually require a wheelchair or other adaptive equipment. Persons affected with EDMD require frequent, at least yearly, heart checkups with a cardiologist. Heart symptoms can appear suddenly with disastrous consequences, so patients often have a pacemaker implanted before they have had any serious heart problem. Anti-arrhythmia drugs, diuretics, ACE inhibitors, and blood thinners may help with some of the cardiovascular symptoms associated with EDMD.
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