GDF6 and Leber congenital amaurosis: Neither were any of the analysed patients shown to harbour rare variants in five recently discovered LCA-associated genes (CCT2, CLUAP1, DTHD1, GDF6, and IFT140)20–24, nor in exon 15 of RPGR, which is an alternative exon called ORF15 that contains highly repetitive purine-rich sequences (Supp.