Childhood-Onset Nemaline Myopathy

Childhood onset nemaline myopathy, or mild nemaline myopathy is a type of nemaline myopathy (NM; see this terms) characterized by distal muscle weakness, and sometimes slowness of muscle contraction.

Epidemiology

The annual incidence of NM has been estimated at 1/50,000 live births.

Clinical description

Childhood onset NM might represent 10-15% of total cases. Onset is around 10 years of age, with initial presentation of symmetric weakness of ankle dorsiflexion and foot drop, or a general slowness of muscle contraction. All movements at the ankle and more proximal limb muscles may be disturbed. Weakness is slowly progressive. Facial, respiratory and cardiac muscles are generally normal, but patients are unable to jump or run because of muscle weakness or slowness.

Etiology

This form of NM is caused by mutations in the ACTA1 (1q42.13), NEB (2q22), TPM2 (9p13.3) or TPM3 (1q21.2) genes, and its transmission follows an autosomal dominant pattern.