POU4F3 and deafness: In this study, using a combination of Pou4f3 mutant and knockout animal models, we examined the pathophysiology and hair cell histopathology of DFNA15 deafness, revealed Pou4f3 haploinsufficiency as the main underlying cause of the deafness, and identified retinoic acid signaling inhibitors for Pou4f3 upregulation and treatment of DFNA15 deafness.