MONDO_0100084 (alpha-actinopathy) is a musculoskeletal system disorder that covers a wide spectrum of phenotypes and is caused by pathogenic variants in the skeletal muscle α-actin gene (ACTA1). These variants lead to a variety of overlapping adult onset and congenital myopathies characterized by muscle weakness, hypotonia, myopathic face, respiratory dysfunction, and rarely cardiac involvement. Specific skeletal muscle structural lesions visible on muscle biopsy include actin accumulations, nemaline and intranuclear bodies, fiber-type disproportion, cores, caps, dystrophic features and zebra bodies. Disorders associated with ACTA1 pathogenic variants can have autosomal dominant (90%) or recessive (10%) inheritance. Also known as: ACTA1 disease, alpha actinopathy.