Cystatin Family Genes encode (Type 2) Cystatin proteins, secreted, tight, reversible, competitive inhibitors of cysteine proteinases that contain multiple cystatin-like sequences and have 2 intrachain disulfide bonds. Cystatin Superfamily Genes comprise three subfamilies that display structural and/or functional similarities: Stefins (Type 1 Cystatins), Cystatins (Type 2 Cystatins), and Kininogens. Some members are active cysteine protease inhibitors; others have lost or never acquired inhibitory activity. (NCI) [ ]