People with nemaline myopathy have moderate weakness in their leg, arm and trunk muscles, accompanied by some mild weakness of the face, tongue and throat muscles. Reflexes are decreased or absent. Affected children often have long, narrow faces with high-arched palates and slender body musculatures. High-arched feet and curvature of the spine are common, and the jaw may also be malformed. The severest form of nemaline myopathy usually appears at birth.
Affected children have a marked weakness and a lack of muscle tone.
Their respiratory muscles are weak, and death often occurs in the first few years of life due to respiratory failure. First described in the 19th century, periodic paralysis is a general term applied to three distinct, though possibly related, nonlethal disorders of voluntary muscle. The three types of periodic paralysis are hypokalemic, hyperkalemic and normokalemic. All three are characterized by intermittent attacks of weakness, during which affected muscles become slack, weak and unable to contract. However, between attacks, the affected muscles usually work normally.