Cystatin B is a protein that functions as a cysteine protease inhibitor, playing a crucial role in regulating enzymes that break down proteins. It is encoded by the CSTB gene and is primarily found in the brain and other tissues. This protein helps maintain the balance of protein degradation and synthesis, which is essential for normal cellular function. Mutations in the CSTB gene can lead to cystatin B deficiency, a condition associated with progressive myoclonus epilepsy type 1 (EPM1). This disorder is characterized by seizures and muscle jerks, highlighting the importance of Cystatin B in neurological health. Understanding this protein can aid in developing treatments for related conditions.