NeurometPlus

Incidence

Autosomal dominant. Alpha-actin (ACTA1) (accounts for 15-25% of nemaline rod myopathies): This mutation is autosomal dominant or sporadic (rare autosomal recessive) missense mutations.

Clinical Characteristics

The typical congenital form presents within the first year of life with hypotonia, generalized limb weakness, facial weakness, feeding difficulty, and mild respiratory weakness. Features such as elongated face, tent-shaped mouth, high-arched palate, and retrognathia are common. Progression is static or very slow, and, after an initial rocky course, stabilization leads to an independent life. Wallgren-Pettersson (1989) reported follow-up of 12 patients with congenital nemaline myopathy. Ten showed clinical deterioration and 2 showed improvement. Muscle weakness was most severe in the facial muscles, flexors of the neck and trunk, dorsiflexors of the feet, and extensors of the toes. Distal limb muscles and limb-girdle muscles were more severely affected than proximal limb muscles. There were no signs of central nervous system involvement. Prognosis was influenced mainly by the presence of scoliosis and restricted respiratory capacity. Ilkovski et al. (2001) reported 3 patients with the condition. The first child had no problems during the neonatal period. At age 5 years, he presented with inability to run and frequent falls. He had poor muscle bulk, pes cavus, and bilateral foot drop. By age 10 years, he showed slowly progressive weakness and involvement of the proximal muscles. The second patient was a 45-year-old man who was physically active and regularly engaged in long-distance competitive cycling, although he had a weak cough and frequent respiratory infections. He had been weak and hypotonic at birth, and showed delayed motor development. The third patient was a 35-year-old woman who had typical congenital nemaline myopathy with neonatal onset of feeding difficulties, respiratory tract infections, hypotonia, facial diplegia, and proximal muscle weakness in the first weeks of life. Her disease was very slowly progressive or nonprogressive. She had an affected younger sib and an affected daughter, consistent with autosomal dominant inheritance. Skeletal muscle biopsy from all patients showed nemaline bodies, although there was marked variability in the percentage of fibers with rods.

Precipitants

None

Provocation Tests

None

Diagnostic Procedures

It is mostly a clinical diagnosis. Muscle biopsy is required. Abnormal threadlike structures in muscle cells. Increased C3 component of serum complement. It is caused by mutation in the alpha-actin gene.