MROH1 is a HEAT repeat protein that functions as a lysosome fission factor essential for maintaining lysosomal homeostasis 1. The protein is recruited to lysosomes by RAB7 (RAB7A or RAB7B) at scission sites, where it homooligomerizes to mediate constriction and scission of lysosomal tubules 1. MROH1 likely severs membranes by inserting amphipathic helices into lipid bilayers 1. This fission activity is critical for maintaining steady-state lysosomal number, morphology, size, and composition, which is essential for proper lysosomal degradation function and cellular regeneration 1. Loss of MROH1 function impairs lysosome fission, resulting in excessive tubular networks that compromise lysosomal integrity and degradation capacity, ultimately affecting cellular development and longevity 1. Beyond its role in lysosomal dynamics, MROH1 copy number deletions correlate with prostate cancer progression independent of disease stage and Gleason grade 2, and genetic variants in MROH1 are associated with axial length variation in ocular development, suggesting broader relevance to refractive error pathogenesis 3.