OSTF1 (osteoclast stimulating factor 1) is an SH3-domain containing protein that functions as a negative regulator of cell motility and bone resorption 1. The protein acts through a signaling cascade that indirectly enhances osteoclast formation and activity, likely via secretion of bone resorption-promoting factors 1. OSTF1 localizes to the cytosol and extracellular regions, facilitating protein-protein interactions critical for cellular functions 2. Structurally, OSTF1 contains ankyrin repeats that enable binding to myosin-1 motors, where it functions as a conserved regulator of membrane association in endocytosis by sequestering myosin-1s in the cytoplasm 34. Clinically, OSTF1 knockout mice exhibit increased trabecular bone mass, confirming its role in bone development 1. OSTF1 is implicated in postmenopausal osteoporosis pathogenesis, where it may regulate the balance between bone formation and resorption 5. Additionally, OSTF1 functions as a protective gene in thyroid cancer prognosis related to natural killer cell immunity 6, and has been associated with cholesteatoma pathogenesis through its involvement in bone destruction 7. Loss of OSTF1 through microdeletion at 9q21.13 has been linked to neurodevelopmental disorders including epilepsy 8.