GJB2 and hearing loss disorder: However, a new Cx30 knockout mouse model with preservation of 50% of Cx26 expression resulted in normal hearing, suggesting that a decrease in Cx26 expression is the main contributing factor in hearing impairment (84) Furthermore, digenic Cx26 and Cx30 heterozygous mutations also lead to hearing loss and a decrease in EP, but no cochlear developmental disorders or cell degeneration (82).