Clarification of glycosylphosphatidylinositol anchorage of OTOANCORIN and human OTOA variants associated with deafness.

Otoancorin (OTOA), encoded by OTOA, is required for the development of the tectorial membrane (TM) in the inner ear. Mutations in this gene cause non-syndromic hearing loss (DFNB22). The molecular mechanisms underlying most of DFNB22 remains poorly understood. Disruption of glycosylphosphatidylinositol (GPI) anchorage has been assumed to be the pathophysiology , mandating experimental validation. From a Korean deaf family, we identified two trans OTOA variants (c.1320+5G>C and p.Gln589ArgfsX55 (NM_144672.3)). Pathogenic potential of c.1320+5G>C was confirmed by a minigene splicing assay. To experimentally determine the GPI anchorage, wildtype and the mutant OTOA harboring p.Gln589ArgfsX55 was expressed in the HEK293T cells. The mutant OTOA with p.Gln589ArgfsX55 resulted in an uncontrolled release of OTOA into the medium in contrast with phosphatidylinositol-specific phospholipase C-induced controlled release of wildtype OTOA from the cell surface. Together, this reverse translational study confirmed GPI-anchorage of OTOA and showed that downstream sequences from the 589th aa is critical for GPI-anchorage. This article is protected by copyright. All rights reserved.