CSTB and Unverricht-Lundborg disease: The CSTB gene is the primary genetic cause of ULD and includes three pathogenic types of variants: 1) homozygous promoter expansions in the CSTB gene (observed in approximately 80–90% of probands), 2) compound heterozygosity for a CSTB dodecamer repeat expansion and a CSTB sequence variant, and 3) homozygosity for a CSTB sequence variant.