COL4A5 belongs to the type IV collagen family. Type IV collagen is the major structural component of glomerular basement membranes (GBM), forming a 'chicken-wire' meshwork together with laminins, proteoglycans and entactin/nidogen. Defects in COL4A5 are the cause of Alport syndrome X-linked (APSX). Deletions covering the N-terminal regions of COL4A5 and COL4A6, which are localized in a head-to-head manner, are the cause of diffuse leiomyomatosis with Alport syndrome (DL-ATS)which also known as esophageal and vulval leiomyomatosis with nephropathy or Alport syndrome and diffuse leiomyomatosis (ATS-DL).