A congenital myopathy that is characterized by severe congenital weakness usually resulting in death from respiratory failure in the first year or so of life and that has_material_basis_in heterozygous mutation in the ACTA1 gene on chromosome 1q42. Heterozygous mutation in the ACTA1 gene can also cause autosomal dominant typical congenital myopathy-2A (CMYP2A). Biallelic mutation in the ACTA1 gene causes autosomal recessive severe infantile congenital myopathy-2B (CMYP2B).