Lastly, the retinal-specific consequences found in our pcdh15b mutants, and not in pcdh15a mutants (Seiler et al., 2005), may provide insight into why particular mutations in PCDH15 are only associated with non-syndromic deafness, whereas others lead to USH1 (Ahmed et al., 2008). Here, PCDH15 is linked to deafness.