Three deafness-related PSGs might also perform roles in balance and spatial orientation: PDZD7 and GRXCR2 are involved in morphogenesis of the sensory hair cells (‘stereocilia’) in the inner ear [85, 86], and TECTA encodes a key protein of the tectorial membrane in which the stereocilia are embedded [87, 88]. The gene discussed is PDZD7; the disease is deafness.