ED MD, which is characterized by early contractures and cardiomyopathy, was first identified as a distinct form of muscular dystrophy in a large Virginia family in 1966.y Generally it is X-linked recessive, although there is an autosomal dominant form, sometimes called Hauptmann-Tannhauser muscular dystrophy. y The incidence of the X-linked type is estimated to be about 1 in 100,000, with the autosomal dominant form being even more rare. One of 10 new X-linked cases may be a new mutation.y
In 1994, the gene for the X-linked type of ED MD was identified as STA at Xq28. y It codes for emerin, a serine-rich protein of 254 amino acids, which resembles membrane proteins of the secretory pathway involved in vesicular transport. y Several different mutations have been reported that result in lack of emerin in skeletal and cardiac muscle.y , y Although the lack of emerin seems to cause the disease, the pathway remains to be established.
The classic symptoms of ED MD include (1) contractures of elbows, Achilles' tendon, and post-cervical muscles before weakness is present; (2) slowly progressive
weakness and muscle wasting, generally starting in the humeroperoneal muscles; and (3) a cardiomyopathy that frequently presents as heart block. A similar disorder, X-linked scapuloperoneal syndrome, that includes color blindness has been linked to Xq28 and may be allelic to ED MD. y
The early contractures and conduction block are features that are helpful in distinguishing this from other muscular dystrophies that may have weakness in the same distribution and the same pattern of inheritance. The main features of the cardiac involvement are impairment of impulse generating cells, variable sinoatrial and atrioventricular conduction defects, increased atrial and ventricular heterotopia, and functional impairment of the myocardium. y Rigid spine syndrome, which occurs sporadically, also has early contractures, but they are limited to the spinal musculature. It usually does not involve cardiac problems. y
The muscle biopsy has nonspecific myopathic or dystrophic changes, including variation in fiber size and fiber necrosis, and endomysial and perimysial fibrosis. Unlike DMD and BMD, there is no alteration in dystrophin. y
The care provided to the patient is similar to that for the other muscular dystrophies, with the notable exception of cardiac intervention. Merlini documented that up to 40 percent of patients with ED MD die suddenly, many of them without any preceding cardiac symptoms. Therefore, a thorough cardiac evaluation, and insertion of a pacemaker when indicated, is essential. Asymptomatic female carriers should be evaluated because they may also have cardiac abnormalities. y
The function of emerin needs to be determined. A recent paper suggests the small size of the STA gene and its housekeeping pattern of expression may make gene therapy possible in ED MD.y
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