Nemaline myopathy is a clinically and genetically heterogeneous condition. The clinical spectrum ranges from severe cases with antenatal or neonatal onset and early death to late onset cases with only slow progression. Three genes are known to cause nemaline myopathy: the genes for nebulin (NEB) on chromosome 2q22, slow alpha-tropomyosin (TPM3) on chromosome 1q21 and skeletal muscle alpha-actin (ACTA1) on chromosome 1q42.