Otopetrins are multi-transmembrane domain proteins that share conserved gene and protein structure and are possibly involved in the formation of otoconia and otoliths. Located in the utricle and saccule of the inner ear, otoconia are complex calcium carbonate biominerals that are required for the normal sensation of gravity and linear acceleration. Vertigo and loss of balance may be attributed to degeneration of displacement of otoconia. The otopetrin family consists of three proteins, OTOP1, OTOP2 and OTOP3. These proteins have 12 putative transmembrane domains that are clustered into three otopetrin domains (OD-I, II and III). OTOP1 was the first described member of the Otopetrin family. Mutations of OTOP1 leads to absence of otoconia or otoliths, though inner ear development is normal. OTOP2 and OTOP3 share significant structural similarity with OTOP1 and may also play a role in the formation of mineralized structures.