Cystatin C (Cystatin-3) is an inhibitor of cysteine proteinases and is thought to serve an important physiological role as a local regulator of this enzymatic activity. Defects in the cystatin C gene (CST3) are the cause of amyloidosis type 6 (AMYL6), also known as hereditary cerebral hemorrhage with amyloidosis (HCHWA), cerebral amyloid angiopathy (CAA),  or cerebroarterial amyloidosis Icelandic type. AMYL6 is a hereditary generalized amyloidosis due to cystatin C amyloid deposition. Cystatin C amyloid accumulates in the walls of arteries, arterioles, and sometimes capillaries and veins of the brain, and in various organs including lymphoid tissue, spleen, salivary glands, and seminal vesicles. Amyloid deposition in the cerebral vessels results in cerebral amyloid angiopathy, cerebral hemorrhage and premature stroke. Cystatin C levels in the cerebrospinal fluid are abnormally low. Genetic variations in CST3 are associated with age-related macular degeneration type 11 (ARMD11). Recombinant Cystatin C comprises a 120 amino acid fragment (27-146) corresponding to the mature Cystatin C protein and is expressed in E. coli with an amino-terminal hexahistidine tag.