Three genes underlying Usher 2 have been identified as USH2A (USH2A),51ADGRV1 (USH2C)52 and WHRN (USH2D).53USH2A mutations are the most common cause of Usher syndrome, accounting for around 80% of Usher 2 cases.34 In addition, PDZ domain-containing 7 (PDZD7) has been reported to act as a disease modifier and contributor to a digenic form of Usher 2.54 This evidence concerns the gene PDZD7 and Usher syndrome.