Retinitis pigmentosa (RP) is the leading cause of blindness with nearly two million people affected worldwide. Many genes have been implicated in RP, yet in 30-80% of the RP patients the genetic cause remains unknown. A similar phenotype, progressive retinal atrophy (PRA), affects many dog breeds including the Miniature Schnauzer. We performed clinical, genetic and functional experiments to identify the genetic cause of PRA in the breed. The age of onset and pattern of disease progression suggested that at least two forms of PRA, types 1 and 2 respectively, affect the breed, which was confirmed by genome-wide association study that implicated two distinct genomic loci in chromosomes 15 and X, respectively. Whole-genome sequencing revealed a fully segregating recessive regulatory variant in type 1 PRA. The associated variant has a very recent origin based on haplotype analysis and lies within a regulatory site with the predicted binding site of HAND1::TCF3 transcription factor complex. Luciferase assays suggested that mutated regulatory sequence increases expression. Case-control retinal expression comparison of six best HAND1::TCF3 target genes were analyzed with quantitative reverse-transcriptase PCR assay and indicated overexpression of EDN2 and COL9A2 in the affected retina. Defects in both EDN2 and COL9A2 have been previously associated with retinal degeneration. In summary, our study describes two genetically different forms of PRA and identifies a fully penetrant variant in type 1 form with a possible regulatory effect. This would be among the first reports of a regulatory variant in retinal degeneration in any species, and establishes a new spontaneous dog model to improve our understanding of retinal biology and gene regulation while the affected breed will benefit from a reliable genetic testing.
Bibliographical noteFunding Information:
This study was partly supported by grants from the Jane and Aatos Erkko Foundation (http://jaes.fi), the Academy of Finland (http://www. aka.fi), HiLife (http://www.helsinki.fi/en/helsinkiinstitute-of-life-science) and Wisdom Health (http:// www.wisdompanel.com) to HL, American Kennel Club Canine Health Foundation (02340) (http:// www.akcchf.org) to HL, the Sigrid Juselius Foundation (http://www.sigridjuselius.fi) to HL, Mary and Georg C. Ehnrooth Foundation (http:// www.marygeorg.fi/saatio.html), Evald and Hilda Nissi Foundation (http://www.nissinsaatio.fi), Orion Research Foundation (http://www.orion.fi/en/rd/ orion-research-foundation/) and Canine Health Research Fund (http://www.helsinki.fi/en/supportus/funds-and-campaigns-you-can-support/canine-health-research-fund) to MK. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
© 2020 Kaukonen et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.