USH2A and Usher syndrome: To date, 12 causative genes and a modifier gene have been identified for the three clinical subtypes of Usher syndrome (USH1, USH2, and USH3), whose clinical definition is based on the progression and severity of hearing impairment, vestibular dysfunction, and retinitis pigmentosa (RP) (Ebermann et al. 2010; Fiskerstrand et al. 2010; Richardson et al. 2011; Bonnet and El-Amraoui 2012; Puffenberger et al. 2012; Riazuddin et al. 2012).