CRB1 and Usher syndrome: Studies have previously reported variants in CRB1, PDE6A, PDE6B, RP1, TULP1, CLRN1, MERTK and CNGA1 causing non-syndromic RP and variants in MYO7A, USH2A, CDH23, USH1H, PCDH15 genes causing USH in families of Pakistani origin [8, 21–28].