Desmin (DES) is a subunit of intermediate filaments in muscles that controls sarcomere architecture. Mutations in desmin that result in excess aggregation of the protein throughout the cell are associated with cardiomyopathy and myofibrillar myopathy diseases. In immunohistochemistry, desmin is commonly used as a mesenchymal marker and is useful for confirming myogenic origin of tissues and distinguishing smooth muscle tumors (desmin positive) from GIST (desmin negative). It is also positive in reactive mesothelial cells, skeletal muscle tumors, leiomyomas and rhabdomyosarcomas. References: Biophysical Reviews. 2018 Aug. 10 (4): 983–1006, PMID: 29926427; Biochimica et Biophysica Acta. 2014 Feb. 1838 (2): 700–22, PMID: 23860255; Journal of Structural Biology. 2014 Nov. 148 (2): 137–52, PMID: 15477095; The American Journal of Cardiology. 2013 Feb. 111 (3): 400–5, PMID: 23168288; Genet Med. 2019 May;21(5):1246-1247, PMID: 30262925