Congenital myopathy

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

The five most common types of congenital myopathies include nonmyelinating myopathy, myotubular myopathy, core myopathy, congenital disproportion of muscle fiber types, and multiple core myopathy. They differ primarily in their histology, symptoms, and prognosis. The diagnosis is suggested by characteristic clinical manifestations and confirmed by muscle biopsy. Treatment consists of physical therapy, which can help maintain function.

Nemyelin myopathy can be autosomal dominant or recessive and develops due to various mutations of genes localized on different chromosomes. Nemaline myopathy in newborns can be severe, moderate and mild. With severe damage, patients may experience weakness of the respiratory muscles and respiratory failure. With moderate damage, progressive weakness of the muscles of the face, neck, trunk and legs develops, but life expectancy can be almost normal. With mild damage, the course is non-progressive, life expectancy is normal.

Myotubular myopathy is autosomal or X-linked. The most common autosomal variant causes mild muscle weakness and hypotonia in patients of both sexes. The X-linked variant affects boys and results in severe skeletal muscle weakness and hypotonia, facial weakness, difficulty swallowing, respiratory muscle weakness, and respiratory failure.

Core myopathy. The inheritance pattern is autosomal dominant. Most patients develop hypotonia and mild proximal muscle weakness in the neonatal period. Many also have facial weakness. The weakness is not progressive and life expectancy is normal. However, these patients have an increased risk of developing malignant hyperthermia (the gene associated with core myopathy is also associated with increased susceptibility to malignant hyperthermia).

Congenital disproportion of muscle fiber types is hereditary, but the mode of inheritance 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 proportion develop respiratory failure.

Multiple core myopathy is usually autosomal recessive but can be autosomal dominant. Infants develop proximal muscle weakness, but some children develop symptoms later and have generalized muscle weakness. Progression varies greatly.

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