Unverricht-Lundborg disease is caused by mutations in the CSTB gene, localized on chromosome 21q22.3 [4], which encodes cystatin B (CSTB): a protease inhibitor that is able to inhibit several lysosomal cysteine proteases in vitro by reversible tight-binding. The gene discussed is CSTB; the disease is Unverricht-Lundborg disease.