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.
Genetic characterization was achieved in 99 of 125 cases (79.2%), with RYR1 most frequently implicated (44/125). Neonatal/infantile onset was observed in 76%. At birth, 30.4% required respiratory support, and 25.2% nasogastric feeding. Twelve percent died, mainly within the first year, associated with mutations in ACTA1, MTM1, or KLHL40. All RYR1-mutated cases survived and did not require long-term ventilator support including those with severe neonatal onset; however, recessive cases were more likely to require gastrostomy insertion (p = 0.0028) compared with dominant cases. Independent ambulation was achieved in 74.1% of all patients; 62.9% were late walkers.