Ectopic expression in L mouse fibroblasts (LM cells) of wild-type CLDN14 protein induced the formation of tight junctions, while both the c.254T>A (p.V85D) mutant, previously identified in a Pakistani family, and the c.301 G>A (p.G101R) mutant, identified in this study through the screen of 183 Spanish and Greek patients affected with sporadic nonsyndromic deafness, failed to form such junctions.