Protocadherin-21 (PCDH21), a candidate gene for human retinal dystrophies.

Purpose: It has been demonstrated that mice lacking a functional copy of prCAD, the gene encoding protocadherin-21, show progressive photoreceptor degeneration. Therefore we searched for a human retinal phenotype associated with mutations in the orthologous human gene, PCDH21.

Methods: We characterized the genomic organization of human PCDH21 and performed mutation screening in 224 patients with autosomal recessive retinitis pigmentosa, 29 patients with Leber congenital amaurosis, and 26 patients with Usher syndrome type 1.

Results: PCDH21 spans 23 kb, consists of 17 exons, and encodes a protein that shows close phylogenetic relationship to cadherin-23 (CDH23), the protein involved in Usher syndrome type 1D. In a total of three unrelated patients, we identified two different heterozygous missense changes (p.A212T and p.P532A), affecting evolutionarily conserved residues, that were not found in 100 unaffected controls. A second mutation allele was not detected. A novel intragenic microsatellite marker was identified.

Conclusions: PCDH21 mutations are not a major cause of the retinal diseases investigated herein, and the corresponding human phenotype remains to be determined. Our data may facilitate future investigations of patients with various (other) forms of inherited retinal dystrophy.