This mutation was expected to generate a null allele because it disrupted the reading frame of Nphp1. However, retinal degeneration in this model was significantly milder than that of Nphp1del20 mice: a slight reduction of the photoreceptor cell layer was observed at postnatal (P) day P21 and 2 months of age, and rhodopsin (RHO) trafficking was only marginally affected. This evidence concerns the gene NPHP1 and retinal degeneration.