Definition:

Autophagic vacuolar myopathies (AVM) are a group of disorders united by shared histopathological features on muscle biopsy that include the aberrant accumulation of autophagic vacuoles. They are characterized by autophagic vacuoles in which the vacuolar membranes have sarcolemmal features, and include four entities: Danon disease, X-linked myopathy with excessive autophagy (XMEA), infantile AVM, and adult onset AVM with multiorgan involvement. Danon disease has been shown to be associated with mutations in the LAMP2 gene located on the X chromosome. XMEA is characterized by weakness and wasting primarily of the proximal muscles of the lower extremities. Mutations in the VMA21 gene at Xq28 cause XMEA by reducing the activity of lysosomal hydrolases.