Disclosed herein are systems for modifying nucleic acid splicing of a target RNA. The system may be useful in a method such as a method for treating a genetic disorder such as epilepsy. The system may include an expression system, or a modified small nuclear RNA (snRNA) that includes an exonic splicing silencer (ESS) sequence, and a target nucleic acid sequence that targets the target RNA. Described herein are recombinant regulatory elements for expression systems. Also described are nucleic acid expression systems with recombinant regulatory elements.