NeurometPlus

Incidence

Nemaline myopathy can be inherited as an autosomal recessive or autosomal dominant condition, but some cases are sporadic, where there is no previous family history of the condition. The most common mode of inheritance is the autosomal recessive. Around 1 in 50,000 individuals are estimated to be affected, and these include both males and females.

Clinical Characteristics

Nemaline, or rod, myopathies are a group of conditions which fall under the umbrella of congenital myopathies. Nemaline rod myopathy involves 20% of congenital myopathies. They are characterised by rod-like structures in the muscle cells, and clinical features such as muscle weakness, breathing problems, and feeding problems. Nemaline' is Greek for 'thread' and the condition is so called because the tiny rod-like structures seen in the affected muscle fibres look like threads. In this severe congenital form, the onset is at birth. Its clinical signs are - Severe floppiness and muscle weakness, little spontaneous movement, difficulties with sucking and swallowing, severe breathing problems. Death usually occurs early. The severe congenital form presents at birth with severe hypotonia and weakness. Lack of movement, poor suck and swallow, and respiratory failure are frequent findings. Death in utero due to fetal akinesia has been described. Arthrogryposis and severe respiratory failure are associated with early death that usually occurs within the first 2 years of life. The cardinal features of nemaline myopathy are weakness and hypotonia, with depressed or absent deep tendon reflexes. Muscle weakness is usually most severe in the face, the neck flexors, and the proximal limb muscles. Extraocular muscles are usually spared. In some individuals with NM, the distal muscles are involved. In congenital forms of nemaline myopathy as this one, the face is often elongated and expressionless, with a tent-shaped mouth, high-arched palate, and retrognathia. Gross motor milestones are delayed. Dysarthria and feeding difficulties are common; approximately 25% of individuals with congenital-onset NM require gavage feeding or gastrostomy during the first few years of life. Respiratory problems secondary to involvement of the diaphragm and intercostal muscles are a common feature of congenital nemaline myopathy. Cardiac contractility is usually normal.

Precipitants

None

Provocation Tests

None

Diagnostic Procedures

It is a clinical diagnosis. Genetic testing show alpha-actin (ACTA1) gen defect (accounts for 15-25% of nemaline rod myopathies): This mutation is autosomal dominant or sporadic (rare autosomal recessive) missense mutations.