Most congenital myopathies are characterized by the presence of a specific structural alteration in muscle fibers, such as nemaline myopathy or central core disease. Nemaline myopathy is an uncommon muscle disease with a wide spectrum of phenotypes, including a congenital form with neonatal onset and fatal outcome, a congenital form with slowly progressive or nonprogressive weakness, and a sporadic adult-onset form. Death due to respiratory insufficiency or recurrent pneumonia is common during the first weeks or months of life. However, the severity of muscle weakness is less marked than in the severe neonatal form. Some patients may present later with delay in attainment of motor milestones.
Respiratory muscles are always involved.
The course of the disease is often static or only very slowly progressive. The late onset or adult onset form of nemaline myopathy is heterogeneous in terms of clinical presentation and disease progression. In patients with an adult onset form of nemaline myopathy, there is often no family history and no symptoms preceding the onset of proximal and distal weakness in the third to sixth decades. A form of sporadic adult-onset nemaline myopathy has been associated with HIV infection. In some patients, there is minimal skeletal muscle involvement and the patient presents with a cardiomyopathy or is detected during the investigation of other family members.