The genetics of eye disorders in the dog

The Demography, Longevity and Mortality of Bullmastiffs Attending Veterinary Practices in Australia

The Bullmastiff is a giant breed of dog, and there is evidence the breed is predisposed to cancer and musculoskeletal disorders, though the disease investigation of the breed is limited. This study reports on the demography, longevity and mortality of Bullmastiffs attending veterinary practices in Australia over a ten-year period. VetCompass Australia collects patient data from veterinary practices across Australia for epidemiological analysis. All patient records of Bullmastiffs available in the VetCompass Australia database during this decade period were reviewed, with demographic information on the breed inclusive of coat colour, sex, neuter status, weight and location collated. Standardised veterinary diagnostic (VeNom) codes for the most appropriate cause of death were assigned to deceased dogs. The population comprised 2771 Bullmastiffs with an overall median age of 2.8 years. Within the group, 1259 were female (45.4%), 1491 were male (53.8%), and 21 dogs (0.8%) had no recorded sex or neuter status. Dogs grew rapidly in their first year, with an average gain of approximately 1 kg every 10 days. A slower growth rate continued in their second year, and growth plateaued as adulthood was reached, with the mean body weight of adult male dogs (46.6 kg) being heavier than that of females (40.5 kg). The age at death for the group was 8.5 years. The most common causes of death in the breed were mass lesions (28.2%), old age (9.9%), musculoskeletal-related disease (9.9%) and neurological (5.3%) and behavioural disorders (4.8%). Neutering was protective against mortality from urogenital causes (OR: 0.14; CI: 0.02-0.52; p = 0.003) and had a positive effect on longevity. This study provides demographic and health information on a population of Bullmastiffs attending veterinary practices in Australia, which will benefit evidence-based veterinary decisions for this breed. Additionally, the results may assist owners and breeders in making informed decisions on health risks and breeding programmes in the population.

Large-scale genomic analysis of the domestic dog informs biological discovery

Recent advances in genomics, coupled with a unique population structure and remarkable levels of variation, have propelled the domestic dog to new levels as a system for understanding fundamental principles in mammalian biology. Central to this advance are more than 350 recognized breeds, each a closed population that has undergone selection for unique features. Genetic variation in the domestic dog is particularly well characterized compared with other domestic mammals, with almost 3000 high-coverage genomes publicly available. Importantly, as the number of sequenced genomes increases, new avenues for analysis are becoming available. Herein, we discuss recent discoveries in canine genomics regarding behavior, morphology, and disease susceptibility. We explore the limitations of current data sets for variant interpretation, tradeoffs between sequencing strategies, and the burgeoning role of long-read genomes for capturing structural variants. In addition, we consider how large-scale collections of whole-genome sequence data drive rare variant discovery and assess the geographic distribution of canine diversity, which identifies Asia as a major source of missing variation. Finally, we review recent comparative genomic analyses that will facilitate annotation of the noncoding genome in dogs.

Exonic Short Interspersed Nuclear Element Insertion in FAM161A Is Associated with Autosomal Recessive Progressive Retinal Atrophy in the English Shepherd

Progressive retinal atrophies (PRAs) are a genetically heterogeneous group of inherited eye diseases that affect over 100 breeds of dog. The initial clinical sign is visual impairment in scotopic conditions, as a consequence of rod photoreceptor cell degeneration. Photopic vision degeneration then follows, due to progression of the disease to the cone photoreceptors, and ultimately results in complete blindness. Two full-sibling English Shepherds were diagnosed with PRA at approximately 5 years old and tested clear of all published PRA genetic variants. This study sought to identify the novel PRA-associated variant segregating in the breed. We utilised a combined approach of whole genome sequencing of the probands and homozygosity mapping of four cases and 22 controls and identified a short interspersed nuclear element within an alternatively spliced exon in FAM161A. The XP_005626197.1 c.17929_ins210 variant was homozygous in six PRA cases and heterozygous or absent in control dogs, consistent with a recessive mode of inheritance. The insertion is predicted to extend exon 4 by 39 aberrant amino acids followed by an early termination stop codon. PRA is intractable to treatment, so the development of a genetic screening test, based on the associated variant, is significant, because it provides dog breeders/owners with a means of reducing the frequency of the disease variant within this breed as well as minimising the risk of breeding puppies that will develop this blinding disease.

A naturally occurring canine model of syndromic congenital microphthalmia

In humans, the prevalence of congenital microphthalmia is estimated to be 0.2-3.0 for every 10,000 individuals, with nonocular involvement reported in ∼80% of cases. Inherited eye diseases have been widely and descriptively characterized in dogs, and canine models of ocular diseases have played an essential role in unraveling the pathophysiology and development of new therapies. A naturally occurring canine model of a syndromic disorder characterized by microphthalmia was discovered in the Portuguese water dog. As nonocular findings included tooth enamel malformations, stunted growth, anemia, and thrombocytopenia, we hence termed this disorder Canine Congenital Microphthalmos with Hematopoietic Defects. Genome-wide association study and homozygosity mapping detected a 2 Mb candidate region on canine chromosome 4. Whole-genome sequencing and mapping against the Canfam4 reference revealed a Short interspersed element insertion in exon 2 of the DNAJC1 gene (g.74,274,883ins[T70]TGCTGCTTGGATT). Subsequent real-time PCR-based mass genotyping of a larger Portuguese water dog population found that the homozygous mutant genotype was perfectly associated with the Canine Congenital Microphthalmos with Hematopoietic Defects phenotype. Biallelic variants in DNAJC21 are mostly found to be associated with bone marrow failure syndrome type 3, with a phenotype that has a certain degree of overlap with Fanconi anemia, dyskeratosis congenita, Shwachman-Diamond syndrome, Diamond-Blackfan anemia, and reports of individuals showing thrombocytopenia, microdontia, and microphthalmia. We, therefore, propose Canine Congenital Microphthalmos with Hematopoietic Defects as a naturally occurring model for DNAJC21-associated syndromes.

Whole-exome sequencing prioritizes candidate genes for hereditary cataract in the Emory mouse mutant

The Emory cataract (Em) mouse mutant has long been proposed as an animal model for age-related or senile cataract in humans-a leading cause of visual impairment. However, the genetic defect(s) underlying the autosomal dominant Em phenotype remains elusive. Here, we confirmed development of the cataract phenotype in commercially available Em/J mice [but not ancestral Carworth Farms White (CFW) mice] at 6-8 months of age and undertook whole-exome sequencing of candidate genes for Em. Analysis of coding and splice-site variants did not identify any disease-causing/associated mutations in over 450 genes known to underlie inherited and age-related forms of cataract and other lens disorders in humans and mice, including genes for lens crystallins, membrane/cytoskeleton proteins, DNA/RNA-binding proteins, and those associated with syndromic/systemic forms of cataract. However, we identified three cataract/lens-associated genes each with one novel homozygous variant including predicted missense substitutions in Prx (p.R167C) and Adamts10 (p.P761L) and a disruptive in-frame deletion variant (predicted missense) in Abhd12 (p.L30_A32delinsS) that were absent in CFW and over 35 other mouse strains. In silico analysis predicted that the missense substitutions in Prx and Adamts10 were borderline neutral/damaging and neutral, respectively, at the protein function level, whereas, that in Abhd12 was functionally damaging. Both the human counterparts of Adamts10 and Abhd12 are clinically associated with syndromic forms of cataract known as Weil-Marchesani syndrome 1 and polyneuropathy, hearing loss, ataxia, retinitis pigmentosa, and cataract syndrome, respectively. Overall, while we cannot exclude Prx and Adamts10, our data suggest that Abhd12 is a promising candidate gene for cataract in the Em/J mouse.

Hereditary Eye Diseases in German Shepherd Dog

Hereditary eye diseases occur to varying degrees in all dog breeds. Individual purebred breeds have specific predispositions to various eye disorders. The German Shepherd is diagnosed mainly with chronic superficial keratitis/pannus, but also with: distichiasis, plasmoma/atypical pannus, corneal dystrophy, persistent pupillary membranes, cataract, cone degeneration, retinal dysplasia, optic nerve hypoplasia/micropapilla, and limbal melanoma. Individual ocular abnormalities are manifested by characteristic clinical manifestations and ophthalmological findings. Some eye diseases can lead to blindness, others affect the comfort of life or work use of the dog to varying degrees. A thorough knowledge of individual ocular pathologies in a particular breed leads not only to the identification of the diagnosis but also to the correct assessment of the dog’s breeding usability.

A multicenter retrospective evaluation of the prevalence of known and presumed hereditary eye diseases in Lagotto Romagnolo dog breed within a referral population in Italy (2012-2020)

OBJECTIVE

To describe the ophthalmological findings of Lagotto Romagnolo dog breed and to report the prevalence of Known and Presumed Hereditary Eye Diseases (KP-HED).

ANIMALS STUDIED

Two hundred sixteen dogs were examined and included in this retrospective study.

PROCEDURES

Medical records of Lagotto Romagnolo dogs between 2012 and 2020 were included. Data about the ocular status were collected through ocular screening examinations (OSE) or clinical ophthalmic examinations (COE). The prevalence of each KP-HED was expressed as a function of the total number of the KP-HED in this referral population.

RESULTS

A total of 85 dogs (39.35%) were ophthalmologically healthy, ocular diseases presumably not hereditary were found in 43 dogs (19.91%), and 88 dogs (40.74%) were affected by one KP-HED. The most common KP-HEDs diagnosed were cataract (28/88; 31.82%), corneal endothelial dystrophy (17/88; 19.32%), retinal dysplasia (9/88; 10.23%), lens instability (7/88; 7.95%), progressive retinal atrophy (6/88, 6.82%), and keratoconjunctivitis sicca (6/88, 6.82%). Most of dogs with a KP-HED (77.27%, 68/88) were identified within COE group.

CONCLUSIONS

To the authors' knowledge, this is the first report of the prevalence of ocular disease in the Lagotto Romagnolo dog breed within a referral population in Italy. This study suggests a relatively high prevalence of KP-HED, with a characteristic late-onset presentation in some diseases. Many of these KP-HED's, lead to ocular pain and irreversible blindness, for this reason, the authors highlight the importance of aiming for an early diagnosis. Breeder's efforts and breeding programs should be directed at limiting such disorders.

Ocular abnormalities in the Icelandic horse with a focus on equine recurrent uveitis: 112 Icelandic horses living in Denmark and 26 Icelandic horses living in the United States

PURPOSE

To describe the most common ocular abnormalities in the Icelandic horse with focus on equine recurrent uveitis (ERU) and association between ocular abnormalities and summer eczema and coat colors.

METHODS

A descriptive cross-sectional study. A complete physical and ophthalmic examination as well as measurement of serum titers for Leptospira serovariants was performed on Icelandic horses from Denmark (DK) and the United States (USA).

RESULTS

One hundred and twelve Icelandic horses living in DK and 26 Icelandic horses living in the United States were included in this study (total of 138 horses, 274 eyes). The three most common ocular abnormalities were follicular conjunctivitis (55.8%, 153/274 eyes), cataracts (27.4%, 75/274 eyes), and multifocal chorioretinopathy ("bullet holes"; 19%, 52/274 eyes). The prevalence for ERU among Icelandic horses aged "eight years and older" was 8% (6/75 horses). The "insidious ERU" type was found in 83% of the ERU cohort (5/6 horses), while "classic ERU" was found in 17% (1/6 horses). A correlation between ERU and cataracts was found in the population (p < .01). Leptospiral serology results were not associated with ERU in either DK or US-Icelandic horses (p = 1.00, p = 1.00, respectively). ERU was not associated with summer eczema (p = .49), and no coat colors were associated with the ocular abnormalities found in the Icelandic horse (all p-values > .05).

CONCLUSION

Follicular conjunctivitis, cataracts, and multifocal chorioretinopathy were the three most common ocular abnormalities findings. Icelandic horses who were 8 years or older had an 8% prevalence for ERU. Summer eczema and coat color were not associated with evidence of ERU or other ocular abnormalities.

Surveying veterinary ophthalmologists to assess the advice given to owners of pets with irreversible blindness

BACKGROUND

The primary purpose of this survey was to determine how veterinary ophthalmologists manage cases of irreversible blindness and to report the most common causes of blindness.

METHODS

Respondents completed a questionnaire sent by email with the cooperation of the American College of Veterinary Ophthalmologists, the European College of Veterinary Ophthalmologists and the Latin American College of Veterinary Ophthalmologists. The questionnaire was developed containing 12 questions with both open and closed multiple-choice response options.

RESULTS

One hundred and eight veterinary ophthalmologists answered the questionnaire. Of the respondents, 83 per cent had graduated for more than 10 years. Glaucoma (63.56 per cent) was the main cited cause of blindness, followed by progressive retinal atrophy (PRA) (17.80 per cent) and retinal detachment (6.78 per cent). The major concerns of owners refer to the impact of blindness on quality-of-life, (39.31 per cent), followed by depression and anxiety (20 per cent), and environment adaptation (11.72 per cent). General recommendations include avoidance of changes in the domestic environment (18.45 per cent), use of auditory stimulation (14.09 per cent) and avoidance of dangerous areas (12.75 per cent). Almost 31 per cent of professionals do not recommend the use of literature on how to deal with blind pets.

CONCLUSIONS

The survey determined glaucoma and PRA as the most common causes of irreversible blindness in pets. Several recommendations that are frequently given to owners of blind pets are presented.

Impact of gene therapy for canine monogenic diseases on the progress of preclinical studies

Rapid progress in knowledge of the organization of the dog genome has facilitated the identification of the mutations responsible for numerous monogenic diseases, which usually present a breed-specific distribution. The majority of these diseases have clinical and molecular counterparts in humans. The affected dogs have thus become valuable models for preclinical studies of gene therapy for problems such as eye diseases, immunodeficiency, lysosomal storage diseases, hemophilia, and muscular dystrophy. Successful gene therapies in dogs have significantly contributed to decisions to run clinical trials for several human diseases, such as Leber's congenital amaurosis 2-LCA2 (caused by a mutation of RPE65), X-linked retinitis pigmentosa-XLRP (caused by mutation RPGR), and achromatopsia (caused by mutation of CNGB3). Promising results were also obtained for canine as follows: hemophilia (A and B), mucopolysaccharidoses (MPS I, MPS IIIB, MPS VII), leukocyte adhesion deficiency (CLAD), and muscular dystrophy (a counterpart of human Duchenne dystrophy). Present knowledge on molecular background of canine monogenic diseases and their successful gene therapies prove that dogs have an important contribution to preclinical studies.

Allele Frequency of the C.5G>A Mutation in the PRCD Gene Responsible for Progressive Retinal Atrophy in English Cocker Spaniel Dogs

Simple Summary

Progressive retinal atrophy (PRA) in English cocker spaniels (ECSs) is associated with progressive rod–cone degeneration (prcd-PRA), an inherited autosomal recessive disease caused by the c.5G>A mutation in the progressive rod–cone degeneration (PRCD) gene. Data regarding the prevalence of the mutated allele are scarce in the global literature, and there is no study evaluating this frequency in Brazil. Therefore, the aim of this study was to evaluate the allele frequency of the c.5G>A mutation in the PRCD gene responsible for progressive retinal atrophy (prcd-PRA) in ECS dogs.

Abstract

Progressive retinal atrophy (PRA) due to the c.5G>A mutation in the progressive rod–cone degeneration (PRCD) gene is an important genetic disease in English cocker spaniel (ECS) dogs. Because the prevalence of this disease has not been verified in Brazil, this study aimed to evaluate the allele frequency of the c.5G>A mutation in the PRCD gene. Purified DNA from 220 ECS dogs was used for genotyping, of which 131 were registered from 18 different kennels and 89 were unregistered. A clinical eye examination was performed in 28 of the genotyped animals; 10 were homozygous mutants. DNA fragments containing the mutation region were amplified by PCR and subjected to direct genomic sequencing. The prcd-PRA allele frequency was 25.5%. Among the registered dogs, the allele frequency was 14.9%; among the dogs with no history of registration, the allele frequency was 41%. Visual impairment was observed in 80% (8/10) of the homozygous mutant animals that underwent clinical eye examination. The high mutation frequency found in this study emphasizes the importance of genotyping ECSs as an early diagnostic test, especially as part of an informed breeding program, to avoid clinical cases of PRA.

A SIX6 Nonsense Variant in Golden Retrievers with Congenital Eye Malformations

Causative genetic variants for more than 30 heritable eye disorders in dogs have been reported. For other clinically described eye disorders, the genetic cause is still unclear. We investigated four Golden Retriever litters segregating for highly variable congenital eye malformations. Several affected puppies had unilateral or bilateral retina dysplasia and/or optic nerve hypoplasia. The four litters shared the same father or grandfather suggesting a heritable condition with an autosomal dominant mode of inheritance. The genome of one affected dog was sequenced and compared to 601 control genomes. A heterozygous private nonsense variant, c.487C>T, was found in the SIX6 gene. This variant is predicted to truncate about a third of the open reading frame, p.(Gln163*). We genotyped all available family members and 464 unrelated Golden Retrievers. All three available cases were heterozygous. Five additional close relatives including the common sire were also heterozygous, but did not show any obvious eye phenotypes. The variant was absent from the 464 unrelated Golden Retrievers and 17 non-affected siblings of the cases. The SIX6 protein is a homeobox transcription factor with a known role in eye development. In humans and other species, SIX6 loss of function variants were reported to cause congenital eye malformations. This strongly suggests that the c.487C>T variant detected contributed to the observed eye malformations. We hypothesize that the residual amount of functional SIX6 protein likely to be expressed in heterozygous dogs is sufficient to explain the observed incomplete penetrance and the varying severity of the eye defects in the affected dogs.

Whole Genome Sequencing of Giant Schnauzer Dogs with Progressive Retinal Atrophy Establishes NECAP1 as a Novel Candidate Gene for Retinal Degeneration

Canine progressive retinal atrophies (PRA) are genetically heterogeneous diseases characterized by retinal degeneration and subsequent blindness. PRAs are untreatable and affect multiple dog breeds, significantly impacting welfare. Three out of seven Giant Schnauzer (GS) littermates presented with PRA around four years of age. We sought to identify the causal variant to improve our understanding of the aetiology of this form of PRA and to enable development of a DNA test. Whole genome sequencing of two PRA-affected full-siblings and both unaffected parents was performed. Variants were filtered based on those segregating appropriately for an autosomal recessive disorder and predicted to be deleterious. Successive filtering against 568 canine genomes identified a single nucleotide variant in the gene encoding NECAP endocytosis associated 1 (NECAP1): c.544G>A (p.Gly182Arg). Five thousand one hundred and thirty canids of 175 breeds, 10 cross-breeds and 3 wolves were genotyped for c.544G>A. Only the three PRA-affected GS were homozygous (allele frequency in GS, excluding proband family = 0.015). In addition, we identified heterozygotes belonging to Spitz and Dachshund varieties, demonstrating c.544G>A segregates in other breeds of German origin. This study, in parallel with the known retinal expression and role of NECAP1 in clathrin mediated endocytosis (CME) in synapses, presents NECAP1 as a novel candidate gene for retinal degeneration in dogs and other species.

Microphthalmia With Multiple Anterior Segment Defects in Portuguese Water Dogs

Portuguese Water Dog breeders and veterinary ophthalmologists recognize microphthalmia with multiple congenital ocular anomalies. Fifteen Portuguese Water Dog puppies (<8 weeks of age; 8 females, 7 males) and 1 adult (5 years old; castrated male) with microphthalmia were examined. The 2 most common abnormalities were microphthalmia (31/32 eyes; 97%) and lens abnormality (congenital cataract or aphakia; 32/32 eyes; 100%). Other common histologic lesions included lack of both a ciliary cleft and trabecular meshwork (15/32 eyes; 47%) and abnormal relationship of anterior segment structures (15/32 eyes; 47%). Many of the observed lesions were similar to those described in various types of anterior segment dysgenesis in humans. Our findings define the histologic lesions in affected Portuguese Water Dogs and suggest a genetic defect that causes anterior segment malformation early in development.

An analysis of anterior segment development in the chicken eye

Precise anterior segment (AS) development in the vertebrate eye is essential for maintaining ocular health throughout life. Disruptions to genetic programs can lead to severe structural AS disorders at birth, while more subtle AS defects may disrupt the drainage of ocular fluids and cause dysregulation of intraocular pressure homeostasis, leading to progressive vision loss. To date, the mouse has served as the major model to study AS development and pathogenesis. Here we present an accurate histological atlas of chick AS formation throughout eye development, with a focus on the formation of drainage structures. We performed expression analyses for a panel of known AS disorder genes, and showed that chick PAX6 was localized to cells of neural retina and surface ectoderm derived structures, displaying remarkable similarity to the mouse. We provide a comparison to mouse and humans for chick AS developmental sequences and structures and confirm that AS development shares common features in all three species, although the main AS structures in the chick are developed prior to hatching. These features enable the unique experimental advantages inherent to chick embryos, and we therefore propose the chick as an appropriate additional model for AS development and disease.

Epidemiology of ocular disorders presumed to be inherited in three small Italian dog breeds in Italy

OBJECTIVE

To describe the prevalence and the types of eye disorders that are known or presumed to be inherited (KP-HED) in three small Italian dog breeds.

ANIMALS

Three small Italian dog breeds: Maltese, Bolognese, and Italian Greyhound.

PROCEDURES

All dogs of the breeds selected for this prospective observational study that underwent a complete ophthalmic examination between 1994 and 2015 were included. General and proportional KP-HED prevalence with 95% confidence intervals were reported.

RESULTS

Three hundred and six of 462 dogs were affected by at least one KP-HED (66.2%; 95% CI: 61.8%-70.4%). In the entire population, the five most common KP-HED were cataract (n = 122; rate on the total number of KP-HED: 31.4%), entropion (n = 56; 14.4%), keratoconjunctivitis sicca (n = 33; 8.5%), retinal dysplasia (n = 24; 6.2%), and persistent pupillary membrane (iris to iris) (n = 21; 5.4%). The most common KP-HED in each breed were cataracts in the Maltese (35.1%) and in the Bolognese (24.2%), and presentation of vitreous in the anterior chamber in the Italian Greyhound (46.7%).

CONCLUSIONS

Clinicians should be aware of KP-HED that commonly affect three small Italian dog breeds. Breed standards should be reconsidered, and breeding programs should be directed at limiting such disorders.

Different allelic frequency of progressive rod-cone degeneration in two populations of Labrador Retrievers in Japan

Progressive rod-cone degeneration (PRCD) is an autosomal recessive disease caused by c.5G>A mutation of the PRCD exon 2. This mutation has been identified in various breeds, including Labrador Retriever. The present study aimed to examine the allelic frequency of PRCD in Labrador Retrievers in Japan. A domestic and a guide dog population were genotyped for PRCD using polymerase chain reaction-restriction fragment length polymorphism. The allelic frequency of c.5G>A in domestic and guide dog populations (0.114 and 0.026, respectively) differed significantly. The allele with c.5G>A mutation appeared to spread widely in the domestic population as compared to that in the guide dog population. This might be the result of mating control for PRCD in the guide dog population.

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.

Epidemiology of ocular disorders presumed to be inherited in three large Italian dog breeds in Italy

OBJECTIVE

To describe the epidemiology and the types of eye disorders that are presumed to be inherited (PIED) in three large Italian dog breeds.

ANIMALS

Three large Italian dog breeds: Neapolitan Mastiff (FCI code: 197), Maremma Sheepdog (FCI code: 201), and Italian Corso dog (FCI code: 343).

PROCEDURES

All dogs that underwent a complete ophthalmic examination between 1992 and 2012 were included in this prospective observational study. The prevalence of eye disorders with 95% confidence intervals was reported for presumed healthy dogs and for dogs referred to a veterinary center for an ophthalmic consultation. Univariate and multivariate logistic regression techniques were used to generate odds ratios.

RESULTS

Of 605 dogs examined during the study period, 351 dogs were affected by at least one PIED (58%; 95% CI: 54-62%). The prevalence of PIED was significantly lower in dogs presented for ophthalmic examination (53.8%) as compared to presumed healthy dogs (62.2%)(OR: 1.4; 95% CI: 1.02-1.9; P = 0.037). Also after multivariate adjustment for the period of observation, the odds of Neapolitan Mastiff (92.1%; OR: 21.4; 95% CI: 11.1-41.4) and of Cane Corso (57.7%; OR: 2.5; 95% CI: 1.7-3.6) suffering a PIED were greater than the Maremma Sheepdog (35.4%). The most common PIED in each breed were entropion (24.3% of all the PIED) in the Neapolitan Mastiff, ectropion (36.6%) in the Corso dog, and cataract (27.9%) in the Maremma Sheepdog.

CONCLUSIONS

Clinicians should be aware that three large Italian dog breeds frequently suffer PIED. Breed standards should be reconsidered, and breeding programs should be directed at limiting such disorders.

Investigation of SLA4A3 as a candidate gene for human retinal disease

SLC4A3 has been shown to cause retinal degeneration in a genetically engineered knockout mouse, and in a naturally occurring form of canine progressive retinal atrophy considered to be the equivalent of retinitis pigmentosa in humans (RP). This study was undertaken to investigate if SLC4A3 coding variants were implicated in human retinal degeneration. SLC4A3 exons were amplified and sequenced in 200 patients with autosomal recessive retinal degeneration who had no known molecular diagnosis for their condition, which included 197 unrelated individuals with suspected RP and three individuals with other forms of retinal disease. Three rare variants were identified that were predicted to be potentially pathogenic, however each variant was heterozygous in a single patient and therefore not considered disease-causing in isolation. Of these three variants, SNP-3 was the rarest, with an allele frequency of 7.06 x 10(-5) (>46,000 exomes from the ExAC database). In conclusion, no compound heterozygous or homozygous potentially pathogenic variants were identified that would account for recessive RP or retinal degeneration in this cohort, however the possibility remains that the rare variants identified could be acting with as yet undiscovered mutations in introns or regulatory regions. SLC4A3 remains an excellent candidate gene for human retinal degeneration, and with the advent of whole exome and whole genome sequencing of cohorts of molecularly unsolved patients with syndromic and non-syndromic forms of retinal degeneration, SLC4A3 may yet be implicated in human disease.

Real-time PCR genotyping assay for canine progressive rod-cone degeneration and mutant allele frequency in Toy Poodles, Chihuahuas and Miniature Dachshunds in Japan

Canine progressive rod-cone degeneration (PRCD) is a middle- to late-onset, autosomal recessive, inherited retinal disorder caused by a substitution (c.5G>A) in the canine PRCD gene that has been identified in 29 or more purebred dogs. In the present study, a TaqMan probe-based real-time PCR assay was developed and evaluated for rapid genotyping and large-scale screening of the mutation. Furthermore, a genotyping survey was carried out in a population of the three most popular breeds in Japan (Toy Poodles, Chihuahuas and Miniature Dachshunds) to determine the current mutant allele frequency. The assay separated all the genotypes of canine PRCD rapidly, indicating its suitability for large-scale surveys. The results of the survey showed that the mutant allele frequency in Toy Poodles was high enough (approximately 0.09) to allow the establishment of measures for the prevention and control of this disorder in breeding kennels. The mutant allele was detected in Chihuahuas for the first time, but the frequency was lower (approximately 0.02) than that in Toy Poodles. The mutant allele was not detected in Miniature Dachshunds. This assay will allow the selective breeding of dogs from the two most popular breeds (Toy Poodle and Chihuahua) in Japan and effective prevention or control of the disorder.