CAST (calpastatin) encodes a specific inhibitor of calpain, a calcium-dependent cysteine protease. The protein exhibits calcium-dependent cysteine-type endopeptidase inhibitor activity and plays important roles in cellular calcium signaling and protein degradation processes. CAST demonstrates RNA binding capabilities and localizes to multiple cellular compartments including cytosol, endoplasmic reticulum, and plasma membrane. The gene has been associated with keratoconus through gene-environment interactions, where specific SNPs (rs26515, rs27991, and rs9314177) in CAST show negative interactions with eye-rubbing behavior 1. This suggests CAST variants may modulate susceptibility to mechanical stress-induced corneal degeneration. Additionally, CAST is linked to a rare genetic condition characterized by peeling skin with leukonychia, acral punctate keratoses, cheilitis, and knuckle pads, indicating its importance in skin integrity and keratinization processes. The protein's role in calcium-dependent processes and protease inhibition makes it functionally relevant for cellular homeostasis and tissue maintenance. However, the provided abstracts primarily focus on CAST-Seq methodology for genome editing analysis rather than the CAST gene itself, limiting detailed mechanistic insights into the protein's specific biochemical functions and disease pathways.