CAPN15 encodes calpain 15, an intracellular cysteine protease belonging to the non-classical small optic lobe (SOL) family of calpains that plays critical roles in vertebrate development 1. The protein exhibits calcium-dependent cysteine-type endopeptidase activity and demonstrates a preference for cleavage at basic residues, particularly lysine 2. CAPN15 is widely expressed throughout the brain and central nervous system, with strongest expression during early development that decreases postnatally 1. In adult mice, expression is particularly prominent in neurons involved in plasticity such as the hippocampus, lateral amygdala, and Purkinje neurons 3. Loss of CAPN15 function is associated with oculogastrointestinal neurodevelopmental syndrome (OGIN), a rare autosomal recessive disorder characterized by developmental eye anomalies including microphthalmia and coloboma, growth deficits, developmental delay, and hearing loss 1. Recent studies have expanded the phenotypic spectrum to include Dandy-Walker malformation and cerebellar anomalies 4. Complete knockout mice exhibit smaller brains with particularly affected thalamus and hippocampal subregions 3, while conditional knockout studies demonstrate roles in adult behavior including self-grooming, motor performance, and fear conditioning 5. The protein appears to have distinct functions in brain development versus adult brain function.