Cdh23 mutations in the mouse are associated with retinal dysfunction but not retinal degeneration

Mutations in the cadherin 23 gene (CDH23) cause Usher syndrome type 1D in humans, a disease that results in retinitis pigmentosa and deafness. Cdh23 is also mutated in the waltzer mouse. In order to determine if the retina of the waltzer mouse undergoes retinal degeneration and to gain insight into the function of cadherin 23 in the retina, we have characterized the anatomy and physiology of retinas of waltzer mouse mutants. Three mutant alleles of Cdh23 were examined by histology and electroretinography (ERG). ERGs of the three Cdh23 mutant groups revealed two of them to have abnormal retinal function. One allele had a- and b-waves that were only approximately 80% of Cdh23 heterozygotes. Another allele had a significantly faster implicit time for both the a- and b-waves of the ERG. No anatomical abnormality was detected in any of the Cdh23 mutants by light microscopy. Because the mutant Cdh23 phenotype was found to be similar to the previously reported retinal phenotype of Myo7a mutant mice, the orthologue of another Usher syndrome (type 1B) gene, we generated mice that carried mutations in both genes to test for genetic interaction in the retina. No functional interaction between cadherin 23 and myosin VIIa was detected by either microscopy or ERG.