is a term for any muscle disorder present at birth. By this definition the congenital myopathies
could include hundreds of distinct neuromuscular
syndromes and disorders. Congenital myopathies do not show evidence for either a progressive dystrophic
process (i.e., muscle
death) or inflammation
, but instead characteristic microscopic changes are seen in association with reduced contractile ability of the muscles. In general, congenital myopathies cause loss of muscle tone and muscle weakness in infancy and delayed motor milestones, such as walking, later in childhood.
Three distinct disorders are definitively classified as congenital myopathies: central core disease
, nemaline rod myopathy
, and centronuclear (myotubular) myopathy
Central core disease is a dominantly inherited genetic disease characterized by mild leg weakness appearing in infancy. This weakness does not progress with age, but leads to delay in walking.
Nemaline rod myopathy is an autosomal dominant or autosomal recessive genetic disease characterized by infantile muscle weakness, loss of muscle tone, and the presence of "nemaline rods" in the muscle, accompanied by problems in suckling or feeding, delay in walking, and occasionally respiratory problems. Other characteristics surface with maturity, such as reduction of muscle bulk, weakness of the trunk and limbs, and development of a long and abnormally shaped face with a protruding jaw. Muscle weakness and wasting may progress slowly throughout life.
Centronuclear (myotubular) myopathy is an inherited genetic disorder in which the nuclei are abnormally found in the center of the muscle fibers. It is characterized by muscle weakness and loss of tone present at birth or by development of muscle weakness later in infancy. Weakness gets gradually worse and can become moderately severe. Infants may have ophthalmoplegia or paralysis of the eye muscles. Centronuclear myopathies occur in three forms:
- The most severe form is present at birth, inherited as an X-linked genetic trait, and can cause severe respiratory muscle weakness. This is the form of centronuclear myopathy currently referred to as myotubular myopathy.
- A less severe form that may present itself at birth or in early childhood progresses slowly and is inherited as an autosomal recessive genetic trait.
- The least severe form first appears during the second and third decades of life and is slowly progressive; it is inherited as an autosomal dominant genetic trait.
Treatment and prognosis
Patients with central core disease generally have a normal life expectancy
with non-progressive muscle weakness. Patients with nemaline rod myopathy may have a normal life expectancy with progressive weakness, or may die early in infancy from respiratory distress
depending upon the severity of the disorder. Patients with centronuclear (myotubular) myopathy generally have a poor prognosis and suffer an early death, usually in infancy. Treatment involves supportive measures to help patients cope with the symptoms of congenital myopathies.