PCDH15 and Oppositional defiant disorder: The genetic cause of the RP was found in 11 of 12 patients with ODD (nine different genes: RP2, RPGR, USH2A, CNGB1, PCDH15/ABCA4, PRPF31, MYO7A, PDE6B, and KLHL7) and in 13 of 18 without ODD (five different genes: RP2, USH2A, PRPF31, BBS1, and AHI1) (6).