Syntaxin 4 is essential for hearing in human and zebrafish

Congenital hearing impairment is a genetically highly heterogenous disorder in which prompt recognition and intervention are crucial to optimize outcomes. In this study, we used exome sequencing to investigate a large consanguineous Pakistani family with eight affected individuals showing bilateral severe-to-profound hearing impairment. This identified a homozygous splice region variant in STX4 (c.232 + 6 T > C), which causes exon skipping and a frameshift, that segregated with hearing impairment (two-point LOD score = 5.9). STX4, a member of the syntaxin family, is a component of the SNARE machinery involved in several vesicle transport and recycling pathways. In silico analysis showed that murine orthologue Stx4a is highly and widespread expressed in the developing and adult inner ear. Immunofluorescent imaging revealed localization of STX4A in the cell body, cell membrane and stereocilia of inner and outer hair cells. Furthermore, a morpholino based knockdown of stx4 in zebrafish showed an abnormal startle response, morphological and developmental defects, and a disrupted mechanotransduction function in neuromast hair cells measured via FM1–43 uptake. Our findings indicate that STX4 dysfunction leads to hearing impairment in humans and zebrafish and supports the evolutionary conserved role of STX4 in inner ear development and hair cell functioning.