A missense variant in IFT122 associated with a canine model of retinitis pigmentosa

Abstract

Retinitis pigmentosa (RP) is a blinding eye disease affecting nearly two million people worldwide. Dogs are affected with a similar illness termed progressive retinal atrophy (PRA). Lapponian herders (LHs) are affected with several types of inherited retinal dystrophies, and variants in PRCD and BEST1 genes have been associated with generalized PRA and canine multifocal retinopathy 3 (cmr3), respectively. However, all retinal dystrophy cases in LHs are not explained by these variants, indicating additional genetic causes of disease in the breed. We collected DNA samples from 10 PRA affected LHs, with known PRCD and BEST1 variants excluded, and 34 unaffected LHs. A genome-wide association study identified a locus on CFA20 (praw = 2.4 × 10–7, pBonf = 0.035), and subsequent whole-genome sequencing of an affected LH revealed a missense variant, c.3176G>A, in the intraflagellar transport 122 (IFT122) gene. The variant was also found in Finnish Lapphunds, in which its clinical relevancy needs to be studied further. The variant interrupts a highly conserved residue, p.(R1059H), in IFT122 and likely impairs its function. Variants in IFT122 have not been associated with retinal degeneration in mammals, but the loss of ift122 in zebrafish larvae impaired opsin transport and resulted in progressive photoreceptor degeneration. Our study establishes a new spontaneous dog model to study the role of IFT122 in RP biology, while the affected breed will benefit from a genetic test for a recessive condition.

Special issue on companion animal genetics: Novel variants discovered in wide variety of diseases in dogs, identification and further characterization of traits in dogs and cats, and the use of microarrays in the detection of aneuploidy in dogs

“…We were very fortunate to have received several submissions from the prolific canine research laboratory of Hannes Lohi (Niskanen et al 2021;Kyöstilä et al 2021;Kaukonen et al 2021;Hytönen et al 2021a,b). In the first paper, Niskanen et al (2021) investigated the known variant in DVL2 associated with kinked tails and brachycephaly in bulldog breeds in an additional 1954 dogs from 15 breeds.…”

“…Although many mutations are known, the Lapponian Herder can have a PRA not explained by these known variants. In this special issue, Kaukonen et al (2021) identify a homozygous missense mutation in the IFT122 gene that may explain the genetic basis for some of the PRA in this breed.…”