A myopathy is a disorder of the muscles that usually results in weakness. Congenital myopathy refers to a group of muscle disorders that appear at birth or in infancy. Typically, an infant with a congenital myopathy will be "floppy," have difficulty breathing or feeding, and will lag behind other babies in meeting normal developmental milestones such as turning over or sitting up.
Muscle weakness can occur for many reasons, including a problem with the muscle, a problem with the nerve that stimulates the muscle, or a problem with the brain. Therefore, to diagnose a congenital myopathy, a neurologist will perform a detailed physical exam as well as tests to determine the cause of weakness. If a myopathy is suspected, possible tests include a blood test for a muscle enzyme called creatine kinase, an electromyogram (EMG) to evaluate the electrical activity of the muscle, a muscle biopsy, and genetic testing.
Major research on disease:
No specific treatment is available for any of the congenital myopathies, but aggressive supportive care is essential to preserve muscle activity, to allow for maximal functional ability, and to prolong life expectancy. The primary concerns affecting prognosis are preventing and correcting skeletal abnormalities (eg, scoliosis, foot deformities, contractures) to maintain ambulation, and to prevent or delay the development of respiratory insufficiency. Respiratory failure due to diaphragmatic weakness can occur at any age and may be independent of the degree of limb weakness. A restrictive pattern on pulmonary function tests (PFTs) may be apparent before the onset of symptoms. Early symptoms of nocturnal hypoxia can include poor sleep, nightmares, morning headache, daytime sleepiness, and weight loss. All patients should have baseline PFTs that are repeated in at least yearly intervals. Treatment options include chest physiotherapy, manually assisted cough, early treatment of respiratory infections, noninvasive ventilation, and tracheostomy combined with permanent ventilation.
Most cases of nemaline myopathy with a known genetic cause result from mutations in one of two genes, NEB or ACTA1. NEB gene mutations account for 50 percent of all cases of nemaline myopathy and ACTA1 gene mutations account for 15 to 25 percent of all cases. When nemaline myopathy is caused by NEB gene mutations, signs and symptoms are typically present at birth or beginning in early childhood. When nemaline myopathy is caused by ACTA1 gene mutations, the condition's severity and age of onset vary widely. Mutations in the other four genes associated with nemaline myopathy each account for only a small percentage of cases.