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Autosomal recessive centronuclear myopathy
Autosomal recessive centronuclear myopathy (AR-CNM) is an inherited neuromuscular disorder defined by numerous centrally placed nuclei on muscle biopsy and clinical features of a congenital myopathy.
The exact prevalence remains unknown.
The age of onset varies from birth to childhood. AR-CNM is characterized by facial weakness including severe involvement of the masticatory muscles, and ocular abnormalities such as ptosis and external ophthalmoplegia. Muscle weakness is seen with variable severity. It is usually prominently proximal, but there may be additional distal weakness and wasting in the lower limbs. Foot abnormalities are frequent and other skeletal deformities (including high arched palate and scoliosis) are common. Respiratory involvement may be severe. An associated cardiomyopathy has been documented in a few, genetically unresolved cases. Urinary incontinence may be an associated feature.
AR-CNM is associated with mutations in the amphiphysin 2 (BIN1) gene on chromosome 2q14.
Diagnosis is based on typical histopathological findings on muscle biopsy in combination with suggestive clinical features. Muscle magnetic resonance imaging and genetic testing are required to confirm the diagnosis and help to distinguish AR-CNM from other forms of CNM.
The main differential diagnoses include other congenital myopathies, myotonic dystrophy and, if facial involvement is prominent, facioscapulohumeral dystrophy (FSH; see these terms).
Genetic counseling should be offered to all patients and their families.
Management and treatment
There is no curative treatment currently available. Management is supportive and based on a multidisciplinary approach.
In the absence of severe cardiorespiratory involvement, the prognosis appears favorable, with mild progressive proximal weakness.