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Emery-Dreifuss muscular dystrophy
Emery-Dreifuss muscular dystrophy (EDMD) is characterized by muscular weakness and atrophy, with early joint contractures and cardiomyopathy.
Prevalence is estimated at 1 in 300,000.
The clinical triad is comprised of contractures of the Achilles, elbow and neck tendons (beginning during early childhood and worsening to result in limited joint movement), slowly progressive muscle weakness and atrophy (initially with a humeroperoneal distribution but later becoming more diffuse) and cardiac anomalies (conduction defects, rhythm disturbances and dilated cardiomyopathy) that usually manifest after age 20 and may lead to sudden death (sometimes the presenting feature of the disease) and ischemic accidents due to embolism. Disease course and severity vary between families and between patients from the same family.
Several causative genes have been identified encoding ubiquitous proteins: emerin (EMD; Xq28 and FHL1; Xq26.3) for X-linked EDMD and lamin A/C (LMNA; 1q21.2) and LUMA (TMEM43) for EDMD with autosomal transmission. Variants in SYNE1and SYNE2 were reported in EDMD-like patients. Emerin, lamin A/C and LUMA are nuclear envelope proteins. Around 45% of patients do not carry mutations in these genes suggesting other causative genes remain to be identified.
Diagnosis relies on recognition of the clinical triad (although the cardiac manifestations may be absent at onset). Muscular imagining may reveal isolated involvement of the soleus, suggestive of the initial stages of 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.
The main differential diagnoses include other forms of myopathy with joint contractures, with or without cardiac involvement (Bethlem myopathy, SEPN1 and FKRP-related myopathies); the desmin-related myopathies; proximal myotonic myopathy; and certain forms of LGMD with cardiac involvement (see these terms).
Prenatal diagnosis is possible when the causative mutation is known.
Several modes of transmission have been reported: X-linked and autosomal dominant or recessive. Genetic counselling depends on the mode of transmission and on whether the mutation has been identified.
Management and treatment
Management should include orthopaedic measures (orthopaedic apparatus, surgery for the Achilles tendon contractures and scoliosis), treatment of the cardiac disease: anti-arrhythmic agents including beta-blockers, diuretics, ACE inhibitors, cardiac implants (pacemaker, implantable cardiac defibrillator), heart transplantation in case of terminal cardiac failure and treatment of the respiratory complications (nasal ventilation, tracheostomy).
Prognosis depends on the severity of the tendon contractures, and of the cardiac and respiratory involvement. Patients with severe forms of the disease may lose the capacity to walk or require intermittent nasal ventilation.
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