Nemaline myopathy is a rare inherited myopathy that primarily affects skeletal muscles, and is characterized by weakness hypotonia, and depressed or absent deep tendon reflexes.  There are six overlapping clinical classification of NM, which are classified by onset and severity of motor and respiratory involvement: severe congenital, Amish, intermediate congenital, typical congenital, childhood-onset, and adult-onset.  The most common type is the typical congenital type (approximately 46%), which is a moderate form of the disease characterized by muscle weakness and feeding problems beginning in infancy.  The severe congenital type (10-20% of patients) is associated with death in the first few months of life, and is characterized by severe hypotonia and little spontaneous movement. Diagnosis of NEM is based on clinical evaluation and histopathological findings on muscle biopsy by the presence of thread- or rod-like structures (nemaline bodies) when stained with Gomori trichrome.

Mutations in the ACTA1 gene account for 15 to 25 percent of all nemaline myopathy cases.  The severity and the age of onset vary widely in patients with mutations in this gene.  Most of these mutations are de novo.  However, some of the cases have been reported with an autosomal dominant and, more rarely, an autosomal recessive inheritance.  The encoded protein is a skeletal alpha (α)-actin, which plays an important role in skeletal muscles, and is an essential component of the sarcomeres.