What is nemaline myopathy (NEM)?

Updated: Mar 11, 2019
  • Author: Matthew Harmelink, MD; Chief Editor: Amy Kao, MD  more...
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Answer

Nemaline (rod) myopathy can be caused by mutations in at least 10 different genes. Of the mutations described, all but one (KBTBD13) is a component or interacts with muscle thin filament. Mutations likely impair the proper formation, maintenance, or function of thin filaments, which results in accumulation of sarcomeric components and formation of nemaline bodies (rods) and associated muscle weakness.

General features of all nemaline myopathies include minimally progressive or nonprogressive proximal limb, bulbar, and facial weakness starting in the neonatal or childhood periods. Additionally, often people present with hypotonia and respiratory insufficiency, which is the most common cause of death.

Skeletal deformities range from arthrogryposis in the severe congenital form to limb contractures, kyphoscoliosis, pectus excavatum, and rigid spine. Cardiomyopathy is rare but can be present early with congenital presentation, or it can be a late complication in childhood-onset or adult-onset cases. CNS disease is rare, but seizures have been reported in severe cases in the neonatal period.

The most common type of nemaline rod myopathy presents in the infantile stage with 42% of patients presenting in the neonatal period. [6]  While there has been an association with polyhydramnios, decreased fetal movements, and an abnormal fetal presentation or fetal distress, these features were only involved in half or less of patients. [6]


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