Cystatin C is a 13-kDa inhibitor of cysteine proteinases which is secreted by all cell types and is completely cleared from the organism through glomerular filtration,shown to be an early and sensitive biomarker of renal dysfunction. A mutation in Cystatin C has been associated with amyloid angiopathy. Expression of this protein in vascular wall smooth muscle cells is severely reduced in both atherosclerotic and aneurysmal aortic lesions,establishing its role in vascular disease. In addition,this protein has been shown to have an antimicrobial function,inhibiting the replication of herpes simplex virus.