Summary
Nemaline myopathy (NM) is a rare hereditary neuromuscular disease characterized by generally nonprogressive muscle weakness of varying severity. The incidence was estimated at 1:50 000 live births in a Finnish study but the disease may be more common in certain populations (Ashkenazi Jewish, Amish community). The age of onset varies from birth to adulthood. The main clinical manifestations include weakness (usually most severe in the face, the neck flexors, and the proximal limb muscles), hypotonia, and depressed or absent deep tendon reflexes. NM is divided into several broad groups classified by onset and severity of motor and respiratory involvement. In the severe neonatal onset group (16% of all NM cases), infants are weak from birth, with feeding, respiratory and cardiac problems that generally lead to death in the first weeks or months of life. The most common form is a mild and nonprogressive (or slowly progressive) childhood disorder. There is weakness in the limb, trunk and facial muscles. Muscular hypotonia is always present during the first year of life. The facial weakness leads to speech and swallowing difficulties. A long face, highly-arched palate, tent shaped mouth, heart problems, kyphoscoliosis, pigeon chest, and pes cavus may be present. Many children with this form of the disease remain active. The adult onset form (which is usually progressive and affects 4% of all individuals with NM) is characterized by respiratory weakening, general weakness in the limbs and, occasionally, constant limb pain. Several genes are involved in the pathogenesis of NM: TPM3, NEB, ACTA1, TNNT1, and TPM2. The disease is inherited as autosomal dominant or autosomal recessive trait. Diagnosis is confirmed by the presence of rod-like structures known as "nemaline bodies" in muscle biopsy samples. Management includes monitoring of nutritional status (special feeding techniques, high-calorie formulas and food, standard care for gastroesophageal reflux), prevention and treatment of lower respiratory tract infections, mechanical ventilation (if indicated), speech therapy, physical and orthopedic therapy for management of scoliosis and joint contractures. Drug therapies (L-tyrosine) are under investigation. *Author: Orphanet (January 2007)*.
