Cystatin S is not an inhibitor of the cysteine proteases but it is able to bind calcium, suggesting that its primary role in the oral environment is likely related to the mineral balance of the tooth [65] while cystatins SN and SA inhibit the human lysosomal cathepsins B, H and L. Interestingly, cathepsin B plays important roles in various models of liver injury, including tumor necrosis factor-α-mediated hepatocyte apoptosis [66], free fatty acid–induced liver damage [67], hepatic ischemia–reperfusion injury [68], and cholestasis [69]. The gene discussed is CST4; the disease is cholestasis.