Progressive retinal atrophy in the Polski Owczarek Nizinny dog: a clinical and genetic study

Preliminary characterization of a novel form of progressive retinal atrophy in the German Spitz dog associated with a frameshift mutation in GUCY2D

OBJECTIVE

To describe the clinical, preliminary electroretinographic and optical coherence tomography features of a newly identified form of progressive retinal atrophy (PRA) in German Spitzes, and identify the causal gene mutation.

ANIMALS

Thirty-three client-owned German Spitz dogs were included.

PROCEDURES

All animals underwent a full ophthalmic examination, including vision testing. In addition, fundus photography, ERG, and OCT were performed. A DNA-marker-based association analysis was performed to screen potential candidate genes and the whole genomes of four animals were sequenced.

RESULTS

Initial fundus changes were pale papilla and mild vascular attenuation. Oscillatory nystagmus was noted in 14 of 16 clinically affected puppies. Vision was impaired under both scotopic and photopic conditions. Rod-mediated ERGs were unrecordable in all affected dogs tested, reduced cone-mediated responses were present in one animal at 3 months of age and unrecordable in the other affected animals tested. Multiple small retinal bullae were observed in three clinically affected animals (two with confirmed genetic diagnosis). OCT showed that despite loss of function, retinal structure was initially well-preserved, although a slight retinal thinning developed in older animals with the ventral retina being more severely affected. Pedigree analysis supported an autosomal recessive inheritance. A mutation was identified in GUCY2D, which segregated with the disease (NM_001003207.1:c.1598_1599insT; p.(Ser534GlufsTer20)). Human subjects with GUCY2D mutations typically show an initial disconnect between loss of function and loss of structure, a feature recapitulated in the affected dogs in this study.

CONCLUSION

We identified early-onset PRA in the German Spitz associated with a frameshift mutation in GUCY2D.

Clinical and Molecular Aspects of C2orf71/PCARE in Retinal Diseases

Mutations in the photoreceptor-specific C2orf71 gene (also known as photoreceptor cilium actin regulator protein PCARE) cause autosomal recessive retinitis pigmentosa type 54 and cone-rod dystrophy. No treatments are available for patients with C2orf71 retinal ciliopathies exhibiting a severe clinical phenotype. Our understanding of the disease process and the role of PCARE in the healthy retina significantly limits our capacity to transfer recent technical developments into viable therapy choices. This study summarizes the current understanding of C2orf71-related retinal diseases, including their clinical manifestations and an unclear genotype-phenotype correlation. It discusses molecular and functional studies on the photoreceptor-specific ciliary PCARE, focusing on the photoreceptor cell and its ciliary axoneme. It is proposed that PCARE is an actin-associated protein that interacts with WASF3 to regulate the actin-driven expansion of the ciliary membrane during the development of a new outer segment disk in photoreceptor cells. This review also introduces various cellular and animal models used to model these diseases and provides an overview of potential treatments.

Animal Welfare Considerations and Ethical Dilemmas Inherent in the Euthanasia of Blind Canine Patients

Simple Summary

Although many dogs with blindness diagnosis can reach a similar age compared to those not affected, often the owners require euthanasia of their animals. This choice leads to conflicting moral principles relating to what is better for the animal and the owner. This article discusses the suitability of euthanasia in blind dogs. To better assess factors influencing the choice of euthanasia, four different scenarios were constructed that described various situations regarding the animal’s aptitude, pet owner, and veterinarian relations.

Abstract

In dogs, several primary or secondary diseases affecting the ocular structures may cause blindness. In cases where the visual impairment is not associated with severe systemic involvement and the animal can still have, predictably, a good “long-term” quality of life, the veterinarian should inform the owner about the differences between humans and animals, concerning the type of visual perception. In the light of the daily findings in veterinary clinic practice, the Authors report four different scenarios with conflicting views between veterinarians and owners about the euthanasia request for a blind dog. They underline how the diagnosis of incipient or already established blindness in dogs can sometimes lead to an inappropriate request for euthanasia.

Genetic Variability in Polish Lowland Sheepdogs Assessed by Pedigree and Genomic Data

Simple Summary

Dogs are an important part of society. The Polish Lowland Sheepdog (PON) is one of 353 of the world’s largest cynological organization listed dog breeds. Breeds with small population sizes, like the PONs, are often characterized by high inbreeding rates and thus an increased risk of congenital diseases. To examine the endangerment of the PONs, measures for genetic diversity and inbreeding were calculated for the German PON population. The study showed that the PONs had to be classified as a minimally endangered population according to threshold values specified by the European Association for Animal Production. However, the very recent trend showed a slight improvement.

Abstract

Genetic variability of Polish Lowland Sheepdog (PON) population was evaluated using both pedigree and genomic data. The analyzed pedigree encompassed 8628 PONs, including 153 individuals genotyped on the Illumina CanineHD BeadChip. Runs of homozygosity (ROH) were defined for homozygous stretches extending over 60 to 4300 kb. The inbreeding coefficients F_Ped based on pedigree data and F_ROH50 based on ROHs were at 0.18 and 0.31. The correlation between both was 0.41 but 0.52 when excluding animals with less than seven complete generations. The realized effective population size (Ne¯) was 22.2 with an increasing trend over years. Five PONs explained 79% of the genetic diversity of the reference population. The effective population size derived from linkage disequilibrium measured by r^² was 36. PANTHER analysis of genes in ROHs shared by ≥50% of the PONs revealed four highly over- or underrepresented biological processes. One among those is the 7.35 fold enriched “forelimb morphogenesis”. Candidate loci for hip dysplasia and patent ductus arteriosus were discovered in frequently shared ROHs. In conclusion, the inbreeding measures of the PONs were high and the genetic variability small compared to various dog breeds. Regarding Ne¯, PON population was minimally endangered according to the European Association for Animal Production.

Complex Structural PPT1 Variant Associated with Non-syndromic Canine Retinal Degeneration

Rod and cone photoreceptors are specialized retinal neurons that have a fundamental role in visual perception, capturing light and transducing it into a neuronal signal. Aberrant functioning of rod and/or cone photoreceptors can ultimately lead to progressive degeneration and eventually blindness. In man, many rod and rod-cone degenerative diseases are classified as forms of retinitis pigmentosa (RP). Dogs also have a comparable disease grouping termed progressive retinal atrophy (PRA). These diseases are generally due to single gene defects and follow Mendelian inheritance.We collected 51 DNA samples from Miniature Schnauzers affected by PRA (average age of diagnosis ∼3.9 ±1 years), as well as from 56 clinically normal controls of the same breed (average age ∼6.6 ±2.8 years). Pedigree analysis suggested monogenic autosomal recessive inheritance of PRA. GWAS and homozygosity mapping defined a critical interval in the first 4,796,806 bp of CFA15. Whole genome sequencing of two affected cases, a carrier and a control identified two candidate variants within the critical interval. One was an intronic SNV in HIVEP3, and the other was a complex structural variant consisting of the duplication of exon 5 of the PPT1 gene along with a conversion and insertion (named PPT1_dci). PPT1_dci was confirmed homozygous in a cohort of 22 cases, and 12 more cases were homozygous for the CFA15 haplotype. Additionally, the variant was found homozygous in 6 non-affected dogs of age higher than the average age of onset. The HIVEP3 variant was found heterozygous (n = 4) and homozygous wild-type (n = 1) in cases either homozygous for PPT1_dci or for the mapped CFA15 haplotype. We detected the wildtype and three aberrant PPT1 transcripts in isolated white blood cell mRNA extracted from a PRA case homozygous for PPT1_dci, and the aberrant transcripts involved inclusion of the duplicated exon 5 and novel exons following the activation of cryptic splice sites. No neurological signs were detected among the dogs homozygous for the PPT1_dci variant. Therefore, we propose PPT1_dci as causative for a non-syndromic form of PRA (PRA_PPT1) that shows incomplete penetrance in Miniature Schnauzers, potentially related to the presence of the wild-type transcript. To our knowledge, this is the first case of isolated retinal degeneration associated with a PPT1 variant.

Characterization of a novel form of progressive retinal atrophy in Whippet dogs: a clinical, electroretinographic, and breeding study

OBJECTIVE

To describe a form of progressive retinal atrophy (PRA) in Whippets including clinical, electroretinographic, optical coherence tomographic changes and pedigree analysis.

ANIMALS STUDIED

Client-owned Whippet dogs (n = 51) living in Brazil.

PROCEDURES

All animals were submitted for routine ophthalmic screening for presumed inherited ocular disease, which included the following: visual tests, such as obstacle course tests, in scotopic and photopic conditions, cotton ball test, dazzle reflex, ocular fundus evaluation by indirect ophthalmoscopy followed by fundus photography. Additionally, electroretinography (ERG) and optical coherence tomography (OCT) were performed in 24 and four dogs, respectively.

RESULTS

Sixteen dogs were diagnosed with PRA. Vision deficits in dim light were detected in dogs examined at a young age associated with nystagmus. Funduscopic changes included the development of multifocal retinal bullae from 6 months of age. Retinal thinning became apparent later, at which time the bullae were no longer detected. OCT examination of selected young dogs revealed that the retinal bullae were due to separation between photoreceptors and the retinal pigment epithelium, and of dogs with more advanced disease confirmed the development of retinal thinning. Electroretinography in young dogs revealed a negative ERG due to a lack of b-wave in both scotopic and photopic recordings. With progression, the ERG became unrecordable. Pedigree analysis suggested an autosomal recessive mode of inheritance.

CONCLUSION

The retinal dystrophy reported here in Whippet dogs has a unique phenotype of an initial lack of ERG b-wave, development of retinal bullae then a progressive generalized retinal degeneration.

Novel retinopathy in related Gordon setters: a clinical, behavioral, electrophysiological, and genetic investigation

PURPOSE

To conduct ophthalmic, behavioral, electrophysiological, and genetic testing on two related Gordon setters presented for day blindness and compare findings with those of nine related and unrelated Gordon setters.

METHODS

All dogs underwent comprehensive ophthalmic examination. Maze testing was conducted under different light intensities. Rod and cone function was assessed electroretinographically. DNA samples were screened for five canine retinal disease gene mutations.

RESULTS

Ophthalmic examination was unremarkable in all dogs. There was no notable difference between day blind dogs and the reference population in scotopic and mesopic maze tests. Day blind dogs performed worse in the photopic maze with slower course completion time and more obstacle collisions. Electroretinography revealed extinguished cone function in day blind dogs and depressed rod responses in all but two reference dogs. One reference population dog presented with day blindness 1 year after initial examination. Mutations that cause achromatopsia (in CNGB3) and cone-rod dystrophies (in ADAM9 and IQCB1) were not detected in any dog tested, although five reference dogs were carriers of the mutation in C2orf71 that causes rod-cone degeneration 4 (rcd4) in Gordon setters and in polski owczarek nizinny dogs.

CONCLUSIONS

This report describes a novel retinopathy in related Gordon setters that has clinical signs and vision testing results consistent with achromatopsia but electroretinographic results suggestive of cone-rod dystrophy. The majority of Gordon setters in this study had low rod responses on electroretinography but it is unclear whether this was indicative of rod dysfunction or normal for the breed. Longer-term observation of affected individuals is warranted.