Leber congenital amaurosis (LCA) is the most severe retinal disease that causes blindness or severe visual impairment within the 1^st year of life. Besides the 19 known LCA genes, the association between other known retinal disease genes and LCA has not been systematically studied. Here we report the largest cohort of LCA patients that is screened for mutations in all known LCA genes and most other known retinal disease genes. We demonstrate for the first time that homozygous mutations in PRPH2 cause LCA. We show that analyzing all possible genes leads to better insights in genotype-phenotype correlations. Our results highlight the importance of molecular diagnosis as an integral part of clinical diagnosis. (By Xia Wang, http://jmg.bmj.com/content/early/2013/07/10/jmedgenet-2013-101558 )