USH2A and retinitis pigmentosa 1: Patient-specific organoids have been differentiated from iPSCs derived from RP patients with different mutations in the following genes: the retinitis pigmentosa GTPase regulator (RPGR) gene, the most common cause of this disease; the beta subunit of the rod cGMP-phosphodiesterase type 6 (PDE6B) gene [69]; the usherin (USH2A) gene, one of the most common causes of non-syndromic RP [70]; the RHO gene [74]; and the pre-mRNA processing factor 31 (PRPF31) gene, which causes one of the most common forms of dominant RP [75].