['The purpose of this study was to identify the causative gene defect in two siblings with an uncharacterized cone-rod dysfunction and to describe the clinical characteristics.', 'Genome-wide homozygosity mapping, with a 250K SNP-array followed by a search for candidate genes, was performed. The patients underwent ophthalmic examination, including elaborate electroretinography.', 'In a Dutch sib pair, a shared 9-Mb homozygous region was found on 11q13.1-q13.5 that encompasses the CABP4 gene, previously implicated in autosomal recessive incomplete congenital stationary night blindness (CSNB2) in two small families. A novel homozygous p.Arg216X mutation in CABP4 was detected in the sib pair. Quantitative RT-PCR on RNA isolated from patient lymphoblast cells showed no nonsense-mediated degradation of mutant CABP4 mRNA. Clinically, patients presented with reduced visual acuity, photophobia, and abnormal color vision, but they did not experience night blindness. Electroretinograms showed electronegative mixed rod-cone responses and severely reduced cone responses, as in CSNB2. Isolated rod responses, however, were (sub)normal.'] Does a novel homozygous nonsense mutation in CABP4 cause congenital cone-rod synaptic disorder?