PCDH15 and hypoparathyroidism-retardation-dysmorphism syndrome: Interestingly, four members of the cadherin family have been linked to retinal degeneration: Mutations in the genes encoding cadherin 23 (CDH23) and protocadherin 15 (PCDH15) cause Usher syndrome (a syndromic form of HRD, characterized by the combination of retinitis pigmentosa [RP] and hearing loss) [4–6], mutations of CDH3, encoding P-cadherin, lead to hypotrichosis with juvenile macular dystrophy [7], and mutations of CDHR1 cause arCRD [8].