Therefore, we tested a hypothesis that rare or common variants in these seven genes, CDHR1, CHM, CRX, ELOVL4, PROM1, PRPH2 and ROM1, known to cause monogenic retinal diseases with overlapping phenotypes with STGD1/ABCA4 disease [8,22,23], can also act as modifiers for the disease in general, or for genetic/phenotypic subgroups. This evidence concerns the gene PRPH2 and Abnormal retinal morphology.