CDH23 and retinal degeneration: We considered another possible explanation for the absence of retinal degeneration in mice homozygous for mutations of Pcdh15 or Cdh23. The Pcdh15av-Jfb phenotype is caused by a single nucleotide insertion (c.2099insC) in exon 17, which causes a frameshift and introduces a premature stop codon in exon 18 [52].