Biallelic mutation of Protocadherin-21 (PCDH21) causes retinal degeneration in humans

PURPOSE To describe the clinical findings and mutations in affected members of two families with an autosomal recessive retinal dystrophy associated with mutations in the protocadherin-21 (PCDH21) gene. METHODS A full genome scan of members of two consanguineous families segregating an autosomal recessive retinal dystrophy was performed and regions identical by descent identified. Positional candidate genes were identified and sequenced. All patients had a detailed ophthalmic examination, including electroretinography and retinal imaging. RESULTS Affected members of both families showed identical homozygosity for an overlapping region of chromosome 10q. Sequencing of a candidate gene, PCDH21, showed two separate homozygous single-base deletions, c.337delG (p.G113AfsX1) and c.1459delG (p.G487GfsX20), which were not detected in 282 control chromosomes. Affected members of the two families first reported nyctalopia in late teenage years and retained good central vision until their late 30s. No color vision was detected in any proband. The fundus appearance included the later development of characteristic circular patches of pigment epithelial atrophy at the macula and in the peripheral retina. CONCLUSIONS Biallelic mutations in the photoreceptor-specific gene PCDH21 cause recessive retinal degeneration in humans.