What are the genetic changes related to nemaline myopathy ?
Mutations in one of many genes can cause nemaline myopathy. These genes provide instructions for producing proteins that play important roles in skeletal muscles. Within skeletal muscle cells, these proteins are found in structures called sarcomeres. Sarcomeres are necessary for muscles to tense (contract). Many of the proteins associated with nemaline myopathy interact within the sarcomere to facilitate muscle contraction. When the skeletal muscle cells of people with nemaline myopathy are stained and viewed under a microscope, these cells usually appear abnormal. These abnormal muscle cells contain rod-like structures called nemaline bodies.  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 about 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 genes associated with nemaline myopathy each account for only a small percentage of cases.  Mutations in any of the genes associated with nemaline myopathy lead to disorganization of the proteins found in the sarcomeres of skeletal muscles. The disorganized proteins cannot interact normally, which disrupts muscle contraction. Inefficient muscle contraction leads to muscle weakness and the other features of nemaline myopathy.  Some individuals with nemaline myopathy do not have an identified mutation. The genetic cause of the disorder is unknown in these individuals.