A novel ACTA1 mutation causing progressive facioscapuloperoneal myopathy in an adult

We report a 58-year-old woman with slowly progressive facio-scapulo-peroneal muscle weakness due to congenital nemaline myopathy (NM) caused by a novel ACTA1 mutation (c.118A>G, p.Met271Val). In adult patients, congenital NM should be distinguished from sporadic late-onset nemaline myopathy (SLONM), which is a treatable acquired muscle disease often associated with monoclonal gammopathy or HIV infection. Both congenital NM and SLONM are characterized by the presence of nemaline rods in muscle. The patient's clinical history of difficulty running since childhood and weakness in other family members favored a congenital NM. The type 1 fiber atrophy and clusters of rods in normal size muscle fibers supported the diagnosis of congenital NM and prompted genetic molecular testing, which led to discovery of the novel ACTA1 variant causative of the myopathy.