Unknown for isoform 4. Csen is involved in calcium-dependent transcriptional repression, regulation of potassium channels, and perhaps in processing of PSEN2 and apoptosis. Isoform 1 or isoform 4 (T+ forms) are expressed at equal levels with isoform 2 or isoform 3 (T- forms) in brain. Lacks EF-hand domains.