COL3A1 (also called collagen III) is a protein that is a type of fibrillar collagen. It is secreted and comprises part of the extracellular matrix. Mutations in the COL3A1 gene are associated with the vascular type of Ehlers-Danlos syndrome, aortic and arterial aneurysms, and collagen type III glomerulopathy. COL3A1 is broadly expressed in most soft connective tissues such as skin, uterus, lung, intestine, and the vascular system, as well as some neoplastic tissues. Staining is used to identify glomerular COL3A1 deposition in collagen type III glomerulopathy. References: Proc Natl Acad Sci U S A. 1997;94(5):1852-1856. doi: 10.1073/pnas.94.5.1852; J Nippon Med Sch. 2008;75(5):254-261. PMID: 19023163; Clin Kidney J. 2015;8(5):543-547. doi: 10.1093/ckj/sfv061; Adv Chronic Kidney Dis. 2012;19(2):101-106. doi: 10.1053/j.ackd.2012.02.017; Clin Nephrol. 2017;87(1):39-46. doi: 10.5414/CN108907