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Congenital Myopathies

By Michael Rubin, MDCM, Weill Cornell Medical College;New York Presbyterian Hospital-Cornell Medical Center

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Congenital myopathy is a term sometimes applied to hundreds of distinct neuromuscular disorders that may be present at birth, but it is usually reserved for a group of rare, inherited, primary muscle disorders that cause hypotonia and weakness at birth or during the neonatal period and, in some cases, delayed motor development later in childhood.

The 4 most common types of congenital myopathy are

  • Nemaline

  • Myotubular

  • Core

  • Congenital fiber type disproportion

The 4 types are distinguished primarily by their histologic features, symptoms, and prognosis. Diagnosis is indicated by characteristic clinical findings and is confirmed by muscle biopsy. Treatment is supportive and includes physical therapy, which may help preserve function.

Nemaline myopathy

This myopathy, the most common congenital myopathy, can be autosomal dominant or recessive. Causative mutations have been identified in 6 genes and all are related to the production of thin-filament proteins. Nemaline myopathy may be severe, moderate, or mild. Severely affected patients may have weakness of respiratory muscles and respiratory failure. Moderate disease causes progressive weakness in muscles of the face, neck, trunk, and feet, but life expectancy may be nearly normal. Mild disease is nonprogressive, and life expectancy is normal.

Myotubular myopathy

This myopathy is X-linked and rare, occurring in about 1/50,000 births. It affects males and results in severe skeletal muscle weakness and hypotonia, facial weakness, impaired swallowing, and respiratory muscle weakness and respiratory failure. Children with milder forms survive to adulthood.

Core myopathies

Inheritance is usually autosomal dominant, but recessive and sporadic forms exist. Core myopathies are characterized by regions (cores) on muscle biopsy specimens in which oxidative enzyme staining is absent; regions may be peripheral or central, focal, multiple, or extensive. Central core myopathy was the first congenital myopathy to be identified.

Most affected patients develop hypotonia and mild proximal muscle weakness as neonates, but sometimes symptoms do not manifest until adulthood. Many also have facial weakness. Weakness is nonprogressive, and life expectancy is normal, but some patients are severely affected and wheelchair bound. The gene mutation associated with central core myopathy is also associated with increased susceptibility to malignant hyperthermia.

Congenital fiber type disproportion myopathy

This myopathy is inherited, but the pattern is poorly understood. Hypotonia and weakness of the face, neck, trunk, and limbs are often accompanied by skeletal abnormalities and dysmorphic features. Most affected children improve with age, but a small percentage develops respiratory failure.

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