Inherited Retinal Diseases in Dogs: Advances in Gene/Mutation Discovery

Inherited retinal diseases in dogs

〔Mini Review〕

Inherited retinal diseases in dogs: advances in gene/mutation discovery

Keiko MIYADERA

School of Veterinary Medicine, University of Pennsylvania, 3900 Delancey St, Philadelphia PA 19104 USA

1. Introduction congenital structural abnormalities due to aberrant Inherited retinal diseases (RDs) in humans comprise a development of the eye (Table 1). Most canine RDs are spectrum of clinically heterogeneous vision-threatening autosomal recessive, while autosomal dominant (Kijas et al. conditions such as retinitis pigmentosa (RP), cone-rod 2002) and X-linked (Acland et al. 1994; Zhang et al. 2002) dystrophy (CRD) and Leber’s congenital amaurosis (LCA). PRAs have been identified. Notably, all canine RDs Since the mapping of the RHO (rhodopsin) gene in a form of molecularly characterized to date have been reported as a RP (Farrar et al. 1990), 221 genes have been associated with monogenic trait (i.e. caused by a mutation in a single gene), human RDs (RetNet; www.sph.uth.tmc.edu/RetNet/), and following a Mendelian inheritance. the number of genes continues to grow. Animal models have been indispensable in validating the physiologic and 2.1. Progressive disorders – PRA and CRD are progressive pathologic mechanisms of these genes, most extensively, as RDs, primarily affecting the photoreceptors. PRA is genetically modified mice. To a lesser degree but with no characterized by initial degeneration of rod photoreceptors less significance, dogs also have received much attention causing night blindness, progressing to total blindness. over the years as a unique, naturally-occurring model of Affected dogs with visual deficits have characteristic fundus RDs. In this review, I will discuss the current knowledge of changes starting from tapetal hyperreflectivity, attenuation the molecular basis of canine RDs and advances in the gene/ of retinal blood vessels, then pale optic disc. CRD is less mutation discovery approach. common, and predominantly affects cone photoreceptors while rods are affected later or to a lesser degree. Early 2. Phenotypic characteristics of canine RDs clinical signs therefore can be day vision problems. The most commonly diagnosed canine RD is However, diagnosis is often made when there is already progressive retinal atrophy (PRA) which is considered extensive day and light visual deficit with end-stage fundic homologous to RP in humans. Dogs affected with PRA changes similar to PRA. As such, CRD may be initially present night blindness, eventually progressing into indistinguishable from PRA at the clinical level, thus often total vision loss. While PRA has been documented in being referred to as PRA. numerous canine breeds, it was once thought to be a single While dogs affected with PRA/CRD show similar disease caused by the same mutation across breeds. fundic changes at the end-stage of the disease, the age of However, breed-specific clinical phenotype (e.g. age of onset and the rate of progression may vary, depending on the onset, rate of progression) together with the evidence from underlying gene/mutation, thereby depending on the breed. diligent mating trials indicated that multiple independent Early-onset PRA/CRD results from abnormal retinal forms of PRAs exist, and that each form is specific to certain development or progressive degeneration starting during or breed(s). Inherited canine RDs may be classified as: soon after retinogenesis. This is followed by a rapid ‘progressive’ that undergo programmed degenerative changes during life;‘ stationary’ that are typically functional Correspondence: Keiko Miyadera, School of Veterinary Medicine, University of Pennsylvania, 3900 Delancey St, Philadelphia PA 19104 abnormalities present at birth (i.e. congenital) showing very USA little progression if at all; and‘ developmental’ that are (E-mail: [email protected])

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progression toward end-stage retinal degeneration, and can are the two critical functional pathways involved in vision. be clinically evident in young adult dogs. Late-onset PRA/ Mutations in genes participating in these pathways may be CRD is characterized by pathological changes after normal associated with RDs, and many of the protein products are development of the retina. As such, they tend to represent localized to the outer retina where these pathways take defects in pathways critical for the long-term maintenance of place. More recently, genes associated with the morphology normal photoreceptors. Visual deficits may not become and function of the photoreceptor connecting cilia have been apparent until well after reproductive maturity, and further associated with RDs, and their roles in normal and diseased progression is typically much slower than in early-onset retina have been a major focus of study (Estrada-Cuzcano et PRA/CRD, and may not become clinically evident until later al. 2012). Of the ~23 genes associated with canine RDs to in life. date, at least 6 genes have implications of a primary role in cilia trafficking. The complex gene-gene interaction 2.2. Stationary disorders – Certain forms of RD show no associated with cilia trafficking remains to be fully or very limited progression. Examples of such stationary unraveled. disorders are achromatopsia (cone degeneration) (Sidjanin et al. 2002) and canine LCA (cLCA), previously known as 4. Advances in canine RD gene/mutation discovery congenital stationary night blindness (CSNB) (Narfström et The gene/mutation discovery approaches for inherited al. 1989). Cones alone are dysfunctional in achromatopsia, canine traits have seen considerable development over the because of a mutation in CNGB3 which is a cone-specific past 20 years. Initial attempts were focused on candidate gene, while both rods and cones are affected in cLCA genes, followed by the introduction of linkage mapping, because of a mutation in RPE65, an RPE-specific positional cloning strategies, and microarray-based genome- isomerohydrolase impairing the retinoid cycle leading to no wide association study (GWAS). More recently, next- 11-cis-retinal being made. While the achromatopsia-affected generation sequencing (NGS) has been implemented with dogs show no further deterioration with age in vision or increasing availability and affordability. retinal abnormalities, elder cLCA-affected dogs show some retinal thinning, both clinically and histologically indicating 4.1. Within-breed genetic uniformity that cLCA originally classified as stationary likely has some Where specific canine breeds are to be established and aspects of a progressive disorder. maintained with their unique traits, admixture of different breeds is prevented. As a result of this‘ breed barrier’, the 2.3. Developmental disorders – Retinal dysplasia is a genetic makeup within a‘ purebred’ dog is typically developmental disorder characterized by a defect in retinal uniform where many sequence variants are fixed. Such differentiation. Syndromic retinal dysplasia in Labrador within-breed genetic uniformity has been both an advantage Retrievers and Samoyeds are oculoskeletal disorders that and a disadvantage in the study of canine genetic traits model autosomal recessive Stickler syndrome in humans (Miyadera et al. 2012a). For example, RDs can be clinically (Goldstein et al. 2010a). Another developmental disorder is variable with regard to the onset, severity, progression, and Collie eye anomaly (CEA) variably affecting the retina- the mode of inheritance in the overall dog population, but choroid-scleral complex ranging from choroidal hypoplasia, within the same breed, they generally show a uniform scleral coloboma to retinal detachment. CEA is considered phenotype; this allows appropriate selection of cases and homologous to macular coloboma in humans. Due to high controls as supposed to humans where multitudes of RD worldwide prevalence of CEA in Collies (70-90%), it is the forms coexist across the population. As the canine breed most common inherited canine RDs, yet impairment of gene pool or genetic variability is limited due to the‘ breed vision is uncommon (Barnett and Stades 1979; Roberts barrier’ as well as the‘ founder/popular-sire effect’, a form 1969). of RD of the same breed is more likely to be caused by the same gene/mutation; while this concept is still valid in many 3. Genes associated with RDs in humans and dogs occasions, as discussed in the following sections, our The phototransduction cascade and the retinoid cycle understanding of the genetic picture of RDs within and

The Journal of Animal Genetics (2014) 42, 79–89 80 Inherited retinal diseases in dogs . 2012) . 2013) . 1993)

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et al . 2002) et al et al et al et al et al et al et al . 2008) et al et al et al et al et al et al et al et al et al et al et al et al et al et al et al References (Clements (Dekomien (Kukekova (Petersen-Jones (Downs (Goldstein (Zangerl (Downs (Downs (Zhang (Zhang (Kijas (Dekomien (Goldstein, personal communication) (Ahonen (Goldstein (Downs and Mellersh. 2014) (Goldstein (Goldstein (Goldstein (Mellersh (Wiik (Sidjanin (Sidjanin (Aguirre (Goldstein (Goldstein (Parker (Guziewicz (Guziewicz (Zangerl Approach Candidate gene Candidate gene LA Candidate gene GWAS LA LA GWAS targeted-NGS GWAS, LA LA Candidate gene LA - GWAS targeted-NGS GWAS, GWAS GWAS (pet, colony) GWAS LA (modifier) GWAS GWAS LA LA Candidate gene LA LA LA Candidate gene Candidate gene Candidate gene Gene Function Phototransduction Phototransduction Phototransduction Phototransduction N.D. N.D. N.D. Anion exchange Cilia formation Cilia trafficking Cilia trafficking Phototransduction N.D. - Phototransduction Phototransduction Cilia trafficking Phototransduction Cilia trafficking N.D. Cilia trafficking Cilia trafficking Phototransduction Phototransduction cycle Visual Collagen formation Collagen formation N.D. Epithelial transport Epithelial transport Epithelial transport

Gene PDE6B PDE6B RD3 PDE6A C2orf71 STK38L PRCD SLC4A3 TTC8 RPGR RPGR RHO CCDC66 - CNGB1 SAG FAM161A PDE6B IQCB1 ADAM9 RPGRIP1 NPHP4 CNGB3 CNGB3 RPE65 COL9A3 COL9A2 NHEJ1 BEST1 BEST1 BEST1 c a b d Breed Irish Setter Sloughi Collie Corgi Welsh Cardigan Setters and others Norwegian Elkhound Multiple breeds Golden Retriever Golden Retriever Samoyed, Siberian Husky Mongrel English Mastiff Bullmastiff, Schapendoes Italian Greyhound Papillon Basenji Spaniel/Terrier Tibetan Terrier American Staffordshire American Pit Bull/Staffordshire Terrier Terrier Glen of Imaal Longhaired/Smooth/ Miniature Dachshunds Wirehaired Dachshund Standard Wirehaired Alaskan Malamute, Miniature Australian shepherd, Siberian Husky German Shorthaired Pointer Briard Labrador Retriever Samoyed Collies and other breeds Multiple breeds Coton de Tulear Lapponian Herder CCDC66 NPHP4 Disease Symbol rcd1 rcd1a rcd2 rcd3 rcd4 erd PRCD GR_PRA1 GR_PRA2 XLPRA1 XLPRA2 ADPRA gPRA IG_PRA1 Pap_PRA1 Bas_PRA1 PRA3 crd1 crd2 crd3 cord1 CRD CD CD cLCA RD/OSD1 RD/OSD2 CEA CMR1 CMR2 CMR3 ISORDERS D ISORDERS ISORDERS D D THERS Table 1. Canine retinal diseases and associated genes 1. Canine retinal Table EVELOPMENTAL ROGRESSIVE (achromatopsia, day blindness) TATIONARY Disease Name P (PRA) Atrophy Retinal Progressive Rod-cone dysplasia 1 Rod-cone dysplasia 1a Rod-cone dysplasia 2 Rod-cone dysplasia 3 Rod-cone dysplasia 4 Early retinal degeneration Progressive rod-cone degeneration 1 Golden Retriever PRA 2 Golden Retriever PRA 1 X-linked PRA 2 X-linked PRA Autosomal dominant PRA Generalized PRA Italian Greyhound PRA Papillon PRA Basenji PRA PRA3 (CRD) Cone-Rod Dystrophy Cone-rod dystrophy Cone-rod dystrophy Cone-rod dystrophy Cone-rod dystrophy Cone-rod dystrophy S Cone degeneration Cone degeneration (achromatopsia, day blindness) Canine LCA D Retinal dysplasia/ Oculo-skeletal dysplasia 1 Retinal dysplasia/ Oculo-skeletal dysplasia 2 Collie eye anomaly O Canine multifocal retinopathy 1 Canine multifocal retinopathy 2 Canine multifocal retinopathy 3 PRCD-affected breeds: American Cocker Spaniel, American Eskimo Dog, Australian Cattle Dog, Australian Shepherd, Australian Stumpy Tail Cattle Dog, Bolonka Zwetna, Chesapeake Bay Retriever, Chinese Crested, English Cocker Dog, Bolonka Zwetna, Chesapeake Bay Retriever, Cattle Tail Australian Stumpy Australian Shepherd, Dog, Australian Cattle Eskimo Dog, American American Cocker Spaniel, breeds: PRCD-affected CEA-affected breeds: Australian Shepherd, Bearded Collie, Boykin Spaniel, Border Collie, Hokkaido Dog, Lancashire Heeler, Nova Scotia Duck Tolling Retriever, Rough/Smooth Collie, Shetland Sheepdog, Silken Windhound, Windhound, Silken Sheepdog, Shetland Collie, Rough/Smooth Retriever, Tolling Duck Scotia Nova Heeler, Lancashire Dog, Hokkaido Collie, Border Spaniel, Boykin Collie, Bearded Shepherd, Australian breeds: CEA-affected CMR1-affected breeds: American Bulldog, Australian Shepherd, Boerboel, Bullmastiff, Cane Corso, Dogue de Bordeaux, Great Pyrenees, Old English Mastiff, Perro de Presa Canario, English/American Bulldog. Cane Corso, Dogue de Bordeaux, Great Pyrenees, Old English Mastiff, Australian Shepherd, Boerboel, Bullmastiff, American Bulldog, breeds: CMR1-affected rcd4-affected breeds: English/Gordon/Irish/Llwellyn Setters, Polish Lowland Sheepdog, Tibetan Terrier. Tibetan breeds: English/Gordon/Irish/Llwellyn Setters, Polish Lowland Sheepdog, rcd4-affected Modiﬁed from Miyadera et al. (2012a). The Approach column shows the method used to identify the chromosomal location and/or the gene, and the type of sample population used. LA, linkage analysis; N.D., The Modiﬁed from Miyadera et al. (2012a). genome-wide association study. not determined; GWAS, a b Norwegian Elkhound, Poodle (Miniature/Toy/Standard), Lapponian Herder, Bear Dog, Kuvasz, Labrador Retriever, Karelian Golden Retriever, Mountain Dog, Finnish Lapphund, Giant Schnauzer, Spaniel, English Shepherd, Entlebucher Terrier. Yorkshire Dog, Swedish Lapphund, Water Dog, Spanish Water Portuguese Retriever, Tolling Nova Scotia Duck c Whippet. Longhaired d

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across canine breeds is becoming more complicated than we inspection to certain genes of interest, a whole genome scan initially thought. When it comes to the mapping process, as interrogates the entire genome necessitating no prior linkage disequilibrium (LD) is extensive within a breed (0.5- assumption or knowledge of the target locus. The current 5Mb, depending on the breed) (Gray et al. 2009; Sutter et al. tools of gene/mutation discovery are based on the 7.5X 2004), increasing the likelihood of two loci within a block of sequence of the Boxer dog (Lindblad-Toh et al. 2005), the chromosome co-segregating, the initial mapping can be done earlier 1.5X Poodle genome sequence (Kirkness et al. 2003), using fewer genetic markers. The disadvantage of long LD as well as single nucleotide polymorphisms (SNPs) after mapping is that a large chromosomal area spanning information across multiple breeds. many genes will need to be studied, and this has often led to Linkage mapping and positional cloning strategies – A a two-step approach of an initial mapping followed by a linkage analysis (LA) mapping utilizes informative families fine-mapping in the search for the causative gene/mutation containing affected and non-affected dogs. Co-segregation of canine RDs. of genetic markers with the phenotype is analyzed to identify recombination, or lack thereof. Subsequently, the 4. 2. Candidate gene analysis region of interest may be further narrowed by fine-mapping, Candidate genes are selected based on existing followed by positional candidate gene analysis. knowledge of the biochemistry or associated diseases, or on Genome-wide association studies (GWAS) –With the information from other species such as humans and mice. development of microarray-based DNA chips, high- Early studies have largely relied on a candidate gene throughput SNP analysis has become feasible in both approach largely because of the lack of alternative canine humans and domestic animals (Andersson 2009). In a genomic tools. GWAS approach, SNP markers pre-determined across the The first canine RD mutation was found by screening a genome are used to assess association with the disease. For candidate gene PDE6B for rcd1 in Irish Setters (Clements et canine traits, the 170K canine SNP chip (Illumina) is the al. 1993; Suber et al. 1993), based on phenotypic and currently most commonly used platform. It has been biochemical similarity to the rd mice with a PDE6B postulated that 20 cases and 20 controls, and 50 cases and 50 mutation (Bowes et al. 1990; Farber and Lolley 1974). controls should be sufficient for mapping autosomal Candidate gene approaches have since identified mutations recessive and dominant traits, respectively using 10,000- for rcd1a in Sloughi dogs (PDE6B) (Dekomien et al. 2000), 30,000 SNPs chips (Lindblad-Toh et al. 2005), due to the for rcd3 in Cardigan Welsh Corgis (PDE6A) (Petersen-Jones conveniently long linkage disequilibrium within a given et al. 1999), and ADPRA in Bullmastiffs and English breed (0.5-5Mb) (Gray et al. 2009; Sutter et al. 2004). Since Mastiffs (RHO) (Kijas et al. 2002). However, while the first report of CRD in Standard Wirehaired Dachshunds successes are often highlighted, there have been too many (Wiik et al. 2008), at least 10 forms of canine RDs have failed candidate gene screening attempts mostly been mapped by GWAS (Table 1). These studies typically unpublished, questioning its efficacy as the primary map a relatively large chromosomal region, followed by approach for mutation discovery in canine RDs (Aguirre- positional candidate gene screening with/without fine Hernandez and Sargan 2005). Further, while there are mapping. hundreds of genes so far associated with human RDs, screening for all the candidate genes has become unrealistic. 4. 4. Next-generation sequencing Still, phenotype-based selection of BEST1 in CMR1, More recently, the next-generation sequencing (NGS) CMR2, and CMR3 has proven to be a success (Guziewicz et technique has been applied to canine RD studies aiding in al. 2007; Zangerl et al. 2010) guided by the high clinical and mapping, fine mapping and functional analysis. NGS is pathologic resemblances to Best macular dystrophy in based on a massively-parallel, high-throughput sequencing humans. which produces millions of short sequences to be analyzed by extensive bioinformatics. A targeted-NGS approach is 4. 3. Whole-genome scan used where a genetic locus has been mapped by a whole Unlike candidate gene studies which limit the genome scan. The genomic area of interest is then captured

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using custom-designed probes, and the enriched DNA is presence of alternative form(s) of RD independent of the subjected to NGS. GWAS-guided fine mapping by targeted- already known RD. Such genetic heterogeneity has been a NGS has so far identified mutations associated with GR_ dilemma for the DNA test providers as well as the users PRA2 in Golden Retrievers (Downs et al. 2014) and PRA3 alike, and those dogs with discordant DNA test results in Tibetan Spaniels/Terriers (Downs & Mellersh 2014). become subjects for further investigation to identify the Exome-sequencing is a form of targeted-NGS which missing RD gene/mutation for the breed. captures only the predetermined known canine exon regions Early-onset PRA in Portuguese Water Dogs (PWD) – for NGS. Ahonen et al. (2013) used exome-sequencing as a PWDs are one of many breeds affected with PRCD-PRA. parallel approach to identify the CNGB1 mutation PRCD in this breed is a late-onset form of PRA typically associated with Papillon PRA. Other NGS applications presenting with night blindness at mid age gradually include RNA-seq and whole-genome sequencing, each of progressing into total blindness. The author and colleagues which has already proven useful in mapping and mutation have recently identified a new form of PRA in PWDs that screening of non-ocular diseases in dogs (Forman et al. are not associated with PRCD. It presents as an early-onset 2012; Drogemuller et al. 2013; Guo et al. 2014). RNA-seq PRA where night blindness is recognized at 1-2 years of age uses tissue-specific RNA as the template and provides a followed by rapid progression to total blindness. Affected complete snapshot of transcripts expressed in the tissue of cases and controls have been identified for a GWAS. interest, allowing assessment of the level of expression (quantitative) as well as structural and sequence changes 5.3. Modifiers (qualitative). While RDs have largely been considered as simple monogenic traits, there is increasing evidence to suggest that 5. Emerging complexity of canine RDs more than one gene mutation could be affecting the 5.1. Multiple forms of RD per breed phenotypic outcome. This is not surprising considering the After a DNA test for certain RD has become available, number of genes (>220) associated with human RDs to date. some of the target breed populations have been found to Genetic polymorphisms in any of these genes albeit non- contain dogs that are tested as genetically“ clear” but are in pathogenic on their own, could potentially function as fact clinically affected with RD (Table 2). This indicates the modifiers altering the effect of a primary mutation. PRCD-

Table 2. Examples of breeds affected with more than one conﬁrmed RDs Breed Disease 1 Disease 2 Disease 3 Disease 4

Australian Shepherd PRCD-PRA CEA CMR1 CD

Golden Retriever PRCD-PRA GR_PRA1 GR_PRA2 -

Goldendoodle PRCD-PRA GR_PRA1 GR_PRA2 -

Norwegian Elkhound PRCD-PRA rd erd -

Lapponian Herder PRCD-PRA CMR3 - -

Irish Setter rcd1-PRA rcd4-PRA - -

Labrador Retriever PRCD-PRA RD/OSD1 - -

Nova Scotia Duck Tolling Retriever PRCD-PRA CEA - -

Miniature Wirehaired Dachshund CRDNPHP4 cord1 - -

Bullmastiff/English Mastiff ADPRA CMR1 - -

Samoyed XLPRA1 RD/OSD2 - -

Tibetan Terrier rcd4-PRA PRA3 - -

Collie rcd2-PRA CEA - -

Portuguese Water Dog PRCD-PRA early-onset PRA - -

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PRA affecting a variety of dog breeds show variable yet Goldendoodles). Meanwhile, new breeds affected with the breed-specific ages of onset. This is thought to be largely existing forms of RDs are found each year and added to the attributed to breed-specific genetic backgrounds that are list. collections of genetic polymorphisms across the genome. The advantage of DNA tests is its ability to detect Modifier genes may or may not be retina-specific, and could unaffected carriers and subclinical cases prior to disease be genes interacting with any retinal gene, further inflating onset. It is important to note that other unidentified forms of the number of potential modifier genes. RDs will not be screened with the existing DNA tests. In The author has previously demonstrated the presence of many situations, following identification of a mutation, a genetic modifier in cone-rod dystrophy 1 (cord1) in coordinated effort is implemented by the breeding Miniature Longhaired Dachshunds (MLHDs). The condition community leading to a substantial decrease in the disease was first described as an autosomal recessive CRD with an and mutant allele frequencies in the breed. Meanwhile, other early-onset (age <1 year) in a MLHD research colony in the non-RD diseases/traits should also be taken into account UK (Curtis & Barnett 1993). This disease was found to when considering breeding strategies to assure the overall segregate completely with a mutation in RPGRIP1, at least health of the breed while nurturing desirable traits. This is within this closed research colony (Mellersh et al. 2006). important as the selective pressure by DNA tests can However, when Japanese pet MLHDs were screened, the significantly reduce the genetic diversity when the mutation age of onset was much broader (4 months - 15 years, mean frequency is high in the breed. In the author’s opinion, the ± SD: 4.6 ± 3.4 years) compared to the UK colony aim of DNA tests is not to eliminate certain dogs from (Miyadera et al. 2009). Furthermore, the Japanese pet breeding, but to safely include them by identifying MLHDs showed significant phenotype-genotype genetically‘ clear’ dogs that can be bred to. Where discordance; 20% of blind cases were not homozygous for maintaining the genetic diversity of the breed population is a the mutation, while 16% of the apparently normal dogs were concern, otherwise desirable dogs may potentially be used homozygous affected genetically. To account for this for breeding as long as a DNA test is performed and disparity, a GWAS was carried out using 80 homozygous breeding is planned accordingly. mutant dogs differing by the clinical phenotypes; this led to the identification of an independently segregating 8. Prospects homozygous modifier locus on chromosome 15 (Miyadera While many successful mapping studies have benefited et al. 2012b). The UK research colony turned out to be from purpose-bred research colonies, cases and controls ‘fixed’ for this modifier locus, thus being masked in the recruited from the general pet population have contributed initial mapping study by Mellersh et al. (2006). The gene/ significantly to the effort. Still, research colonies remain mutation underlying this modifier and its interaction with essential in providing adequate resources for functional RPGRIP1 is current our focus of study. studies and developing new therapies. Identification of genes/mutations underlying canine RDs have provided 7. DNA tests excellent testing grounds for gene replacement therapy, one DNA tests for most canine RDs whose underlying of the approaches under active development to prevent, mutation is known are available commercially (Mellersh stabilize, or reverse the retinal degenerative process in 2012). Unlike in the human population with a huge amount humans and animals. of genetic heterogeneity requiring screening of an extensive cLCA in Briards with an RPE65 mutation has been panel of genes and mutations (Stone 2007; Zernant et al. treated successfully with subretinal injection of a 2005), in dogs, testing of only the known mutation(s) recombinant adeno-associated virus 2 carrying wild-type associated with the respective breed is often sufficient. RPE65 (Acland et al. 2001; Narfström et al. 2003). The Notably, a mix dog produced from different canine breeds single injection was safe, effective and stable with functional which happen to harbor the same RD mutation can be improvement up to four years (Acland et al. 2005; Narfstrom affected with that RD such as PRCD-PRA seen among the et al. 2008). The treatment was subsequently applied to increasingly popular‘ designer dogs’ (e.g. Labradoodles, human LCA patients carrying RPE65 mutations leading to

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significant restorations of vision (Bainbridge et al. 2008; X-linked trait. American Journal Medical Genetics 52, Hauswirth et al. 2008; Maguire et al. 2008). Successful gene 27-33. therapy using the dog model has also been achieved in Aguirre-Hernandez J, Sargan DR (2005) Evaluation of achromatopsia (Komaromy et al. 2010) and CMR candidate genes in the absence of positional (Guziewicz, personal communication). information: a poor bet on a blind dog! Journal of Heredity 96, 475-484. 9. Conclusion Aguirre GD, Baldwin V, Pearce-Kelling S, Narfstrom K, Since the first identification of the PDE6B mutation in Ray K, Acland GM (1998) Congenital stationary night 1993, significant progress has been made in the molecular blindness in the dog: common mutation in the RPE65 study of canine RDs thanks to the development of genetic gene indicates founder effect. Molecular Vision 4, resources and tools. Phenotypic and genetic similarities 23-29. between canine and human RDs have provided an excellent Ahonen SJ, Arumilli M, Lohi H (2013) A CNGB1 frameshift opportunity to study the molecular mechanisms across mutation in Papillon and Phalène dogs with progressive species. Molecular characterization of canine RDs is likely retinal atrophy. PLoS One. 2013 Aug 28;8(8):e72122. to become even faster and affordable over the coming years, Andersson L (2009) Genome-wide association analysis in with increasing feasibility of the NGS approach. Due to the domestic animals.: a powerful approach for genetic history of breed development, the genomic background dissection of trait loci. Genetica 136, 341-349 within each dog breed is relatively uniform compared to the Bainbridge JW, Smith AJ, Barker SS, Robbie S, Henderson extremely heterogeneous human population as a whole. R, Balaggan K, Viswanathan A, Holder GE, Stockman Identification of primary mutations and manageable number A, Tyler N, Petersen-Jones S, Bhattacharya SS, of minor alleles or modifiers should therefore be more Thrasher AJ, Fitzke FW, Carter BJ, Rubin GS, Moore advantageous using the canine population, and will continue AT, Ali RR (2008) Effect of gene therapy on visual to contribute in the understanding of RDs in dogs and in function in Leber’s congenital amaurosis. New England humans. Journal of Medicine 358, 2231-2239. Acknowledgement: The author wishes to thank Dr. Gustavo Barnett K, Stades F (1979) Collie eye anomaly in the Aguirre, University of Pennsylvania for valuable Shetland sheepdog in the Netherlands. Journal of Small discussions. The author is supported by the Career Animal Practice 20, 321-329. Development Award for Veterinary Residents from the Bowes C, Li T, Danciger M, Baxter LC, Applebury ML, Foundation Fighting Blindness. Farber DB (1990) Retinal degeneration in the rd mouse Is caused by a defect in the ß subunit of rod cGMP- References phosphodiesterase. Nature 347, 677-680. Acland GM, Aguirre GD, Bennett J, Aleman TS, Cideciyan Clements PJM, Gregory CY, Peterson-Jones SM, Sargan AV, Bennicelli J, Dejneka NS, Pearce-Kelling SE, DR, Bhattacharya SS (1993) Confirmation of the rod Maguire AM, Palczewski K, Hauswirth WW, Jacobson cGMP phosphodiesterase ß subunit (PDEß) nonsense SG (2005) Long-term restoration of rod and cone vision mutation in affected rcd-1 Irish setters in the UK and by single dose rAAV-mediated gene transfer to the development of a diagnostic test. Current Eye Research retina in a canine model of childhood blindness. 12, 861-866. Molecular Therapy 12, 1072-1082. Curtis R, Barnett KC (1993) Progressive retinal atrophy in Acland GM, Aguirre GD, Ray J, Zhang Q, Aleman TS, miniature longhaired dachshund dogs. British Cideciyan AV, Pearce-Kelling SE, Anand V, Zeng Y, Veterinary Journal 149, 71-85. Maguire AM, Jacobson SG, Hauswirth WW, Bennett J Dekomien G, Runte M, Godde R, Epplen JT (2000) (2001) Gene therapy restores vision in a canine model Generalized progressive retinal atrophy of Sloughi dogs of childhood blindness. Nature Genetics 28, 92-95. is due to an 8-bp insertion in exon 21 of the PDE6B Acland GM, Blanton SH, Hershfield B, Aguirre GD (1994) gene. Cytogenetics Cell Genetics 90, 261-267. XLPRA: a canine retinal degeneration inherited as an Dekomien G, Vollrath C, Petrasch-Parwez E, Boeve MH,

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Akkad DA, Gerding WM, Epplen JT (2010) Progressive identification of a disease associated SPTBN2 mutation. retinal atrophy in Schapendoes dogs: mutation of the BMC Genetics, 13, 55. doi:10.1186/1471-2156-13-55. newly identified CCDC66 gene. Neurogenetics 11, 163- Goldstein O, Guyon R, Kukekova A, Kuznetsova TN, 174. Pearce-Kelling SE, Johnson J, Aguirre GD, Acland GM Downs LM, Wallin-Hakansson B, Boursnell M, Marklund S, (2010a) COL9A2 and COL9A3 mutations in canine Hedhammar A, Truve K, Hubinette L, Lindblad-Toh K, autosomal recessive oculoskeletal dysplasia. Bergstrom T, Mellersh CS (2011) A Frameshift Mammalian Genome 21, 398-408. Mutation in Golden Retriever Dogs with Progressive Goldstein O, Kukekova AV, Aguirre GD, Acland GM Retinal Atrophy Endorses SLC4A3 as a Candidate Gene (2010b) Exonic SINE insertion in STK38L causes for Human Retinal Degenerations. PLoS One 6, e21452. canine early retinal degeneration (erd). Genomics 96, Downs LM, Bell JS, Freeman J, Hartley C, Hayward LJ, & 362-368. Mellersh CS. (2013). Late-onset progressive retinal Goldstein O, Mezey JG, Boyko AR, Gao C, Wang W, atrophy in the Gordon and Irish Setter breeds is Bustamante CD, Anguish LJ, Jordan JA, Pearce-Kelling associated with a frameshift mutation in C2orf71. SE, Aguirre GD, Acland GM (2010c) An ADAM9 Animal Genetics, 44(2), 169–77. mutation in canine cone-rod dystrophy 3 establishes Downs LM, Wallin-Håkansson B, Bergström T, Mellersh homology with human cone-rod dystrophy 9. Molecular CS. (2014) A novel mutation in TTC8 is associated with Vision 16, 1549-1569. progressive retinal atrophy in the golden retriever. Goldstein O, Jordan JA, Aguirre GD, Acland GM. (2013a). Canine Genetics and Epidemiology 1:4. A non-stop S-antigen gene mutation is associated with Downs LM and Mellersh CS. (2014) An Intronic SINE late onset hereditary retinal degeneration in dogs. Insertion in FAM161A that Causes Exon-Skipping Is Molecular Vision, 19, 1871–1884. Associated with Progressive Retinal Atrophy in Tibetan Goldstein O, Mezey JG, Schweitzer PA, Boyko AR, Gao C, Spaniels and Tibetan Terriers. PLoS One 9:4, e93990. Bustamante CD, Jordan JA, Aguirre GD, Acland GM Drögemüller M, Jagannathan V, Howard J, Bruggmann R, (2013b) IQCB1 and PDE6B mutations cause similar Drögemüller C, Ruetten M, Leeb T, Kook PH. (2014). A early onset retinal degenerations in two closely related frameshift mutation in the cubilin gene (CUBN) in terrier dog breeds. Investigative Ophthalmology & Beagles with Imerslund-Gräsbeck syndrome (selective Visual Science 25;54(10):7005-19. cobalamin malabsorption). Animal Genetics, 45(1), Gray MM, Granka JM, Bustamante CD, Sutter NB, Boyko 148–50. AR, Zhu L, Ostrander EA, Wayne RK (2009) Linkage Estrada-Cuzcano A, Roepman R, Cremers FP, den Hollander disequilibrium and demographic history of wild and AI, Mans DA (2012) Non-syndromic retinal domestic canids. Genetics 181, 1493-1505. ciliopathies: translating gene discovery into therapy. Guo J, Johnson GS, Brown HA, Provencher ML, Ronaldo Human Molecular Genetics 15;21(R1):R111-24. C, Mhlanga-mutangadura T, Taylor JF, Schnabel RD, Farber D, Lolley R (1974) Cyclic guanosine O’Brien DP, Katz ML. (2014). A CLN8 nonsense monophosphate: elevation in degenerating mutation in the whole genome sequence of a mixed photoreceptor cells of the C3H mouse retina. Science breed dog with neuronal ceroid lipofuscinosis and 186, 449-451. Australian Shepherd ancestry. Molecular Genetics and Farrar GJ, McWilliam P, Bradley DG, Kenna P, Lawler M, Metabolism, 112, 302–309. Sharp EM, Humphries MM, Eiberg H, Conneally PM, Guziewicz KE, Zangerl B, Lindauer SJ, Mullins RF, Trofatter JA, et al. (1990) Autosomal dominant retinitis Sandmeyer LS, Grahn BH, Stone EM, Acland GM, pigmentosa: linkage to rhodopsin and evidence for Aguirre GD (2007) Bestrophin gene mutations cause genetic heterogeneity. Genomics 8, 35-40. canine multifocal retinopathy: a novel animal model for Forman OP, De Risio L, Stewart J, Mellersh CS, Beltran E. best disease. Investigative Ophthalmology & Visual (2012). Genome-wide mRNA sequencing of a single Science 48, 1959-1967. canine cerebellar cortical degeneration case leads to the Hauswirth WW, Aleman TS, Kaushal S, Cideciyan AV,

The Journal of Animal Genetics (2014) 42, 79–89 86 Inherited retinal diseases in dogs

Schwartz SB, Wang L, Conlon TJ, Boye SL, Flotte TR, Decktor K, Degray S, Dhargay N, Dooley K, Dooley K, Byrne BJ, Jacobson SG (2008) Treatment of leber Dorje P, Dorjee K, Dorris L, Duffey N, Dupes A, congenital amaurosis due to RPE65 mutations by ocular Egbiremolen O, Elong R, Falk J, Farina A, Faro S, subretinal injection of adeno-associated virus gene Ferguson D, Ferreira P, Fisher S, Fitzgerald M, Foley K, vector: short-term results of a phase I trial. Human Gene Foley C, Franke A, Friedrich D, Gage D, Garber M, Therapy 19, 979-990. Gearin G, Giannoukos G, Goode T, Goyette A, Graham Kijas JW, Cideciyan AV, Aleman TS, Pianta MJ, Pearce- J, Grandbois E, Gyaltsen K, Hafez N, Hagopian D, Kelling SE, Miller BJ, Jacobson SG, Aguirre GD, Hagos B, Hall J, Healy C, Hegarty R, Honan T, Horn A, Acland GM (2002) Naturally occurring rhodopsin Houde N, Hughes L, Hunnicutt L, Husby M, Jester B, mutation in the dog causes retinal dysfunction and Jones C, Kamat A, Kanga B, Kells C, Khazanovich D, degeneration mimicking human dominant retinitis Kieu AC, Kisner P, Kumar M, Lance K, Landers T, Lara pigmentosa. Proceedings National Acadademy of M, Lee W, Leger JP, Lennon N, Leuper L, Levine S, Liu Sciences, USA 99, 6328-6333. J, Liu X, Lokyitsang Y, Lokyitsang T, Lui A, Macdonald Kirkness EF, Bafna V, Halpern AL, Levy S, Remington K, J, Major J, Marabella R, Maru K, Matthews C, Rusch DB, Delcher AL, Pop M, Wang W, Fraser CM, McDonough S, Mehta T, Meldrim J, Melnikov A, Venter JC (2003) The dog genome: survey sequencing Meneus L, Mihalev A, Mihova T, Miller K, Mittelman and comparative analysis. Science 301, 1898-1903. R, Mlenga V, Mulrain L, Munson G, Navidi A, Naylor Komaromy AM, Alexander JJ, Rowlan JS, Garcia MM, J, Nguyen T, Nguyen N, Nguyen C, Nguyen T, Nicol R, Chiodo VA, Kaya A, Tanaka JC, Acland GM, Hauswirth Norbu N, Norbu C, Novod N, Nyima T, Olandt P, O’ WW, Aguirre GD (2010) Gene therapy rescues cone Neill B, O’Neill K, Osman S, Oyono L, Patti C, Perrin function in congenital achromatopsia. Human D, Phunkhang P, Pierre F, Priest M, Rachupka A, Molecular Genetics 19, 2581-2593. Raghuraman S, Rameau R, Ray V, Raymond C, Rege F, Kukekova AV, Goldstein O, Johnson JL, Richardson MA, Rise C, Rogers J, Rogov P, Sahalie J, Settipalli S, Pearce-Kelling SE, Swaroop A, Friedman JS, Aguirre Sharpe T, Shea T, Sheehan M, Sherpa N, Shi J, Shih D, GD, Acland GM (2009) Canine RD3 mutation Sloan J, Smith C, Sparrow T, Stalker J, Stange- establishes rod-cone dysplasia type 2 (rcd2) as ortholog Thomann N, Stavropoulos S, Stone C, Stone S, Sykes S, of human and murine rd3. Mammalian Genome 20, Tchuinga P, Tenzing P, Tesfaye S, Thoulutsang D, 109-123. Thoulutsang Y, Topham K, Topping I, Tsamla T, Lindblad-Toh K, Wade CM, Mikkelsen TS, Karlsson EK, Vassiliev H, Venkataraman V, Vo A, Wangchuk T, Jaffe DB, Kamal M, Clamp M, Chang JL, Kulbokas EJ, Wangdi T, Weiand M, Wilkinson J, Wilson A, Yadav S, Zody MC, Mauceli E, Xie X, Breen M, Wayne RK, Yang S, Yang X, Young G, Yu Q, Zainoun J, Zembek L, Ostrander EA, Ponting CP, Galibert F, Smith DR, Zimmer A, Lander ES (2005) Genome sequence, Dejong PJ, Kirkness E, Alvarez P, Biagi T, Brockman comparative analysis and haplotype structure of the W, Butler J, Chin CW, Cook A, Cuff J, Daly MJ, domestic dog. Nature 438, 803-819. Decaprio D, Gnerre S, Grabherr M, Kellis M, Kleber M, Maguire AM, Simonelli F, Pierce EA, Pugh EN, Jr., Bardeleben C, Goodstadt L, Heger A, Hitte C, Kim L, Mingozzi F, Bennicelli J, Banfi S, Marshall KA, Testa Koepfli KP, Parker HG, Pollinger JP, Searle SM, Sutter F, Surace EM, Rossi S, Lyubarsky A, Arruda VR, NB, Thomas R, Webber C, Baldwin J, Abebe A, Konkle B, Stone E, Sun J, Jacobs J, Dell’Osso L, Hertle Abouelleil A, Aftuck L, Ait-Zahra M, Aldredge T, Allen R, Ma JX, Redmond TM, Zhu X, Hauck B, Zelenaia O, N, An P, Anderson S, Antoine C, Arachchi H, Aslam A, Shindler KS, Maguire MG, Wright JF, Volpe NJ, Ayotte L, Bachantsang P, Barry A, Bayul T, Benamara McDonnell JW, Auricchio A, High KA, Bennett J M, Berlin A, Bessette D, Blitshteyn B, Bloom T, Blye J, (2008) Safety and efficacy of gene transfer for Leber’s Boguslavskiy L, Bonnet C, Boukhgalter B, Brown A, congenital amaurosis. New England Journal of Cahill P, Calixte N, Camarata J, Cheshatsang Y, Chu J, Medicine 358, 2240-2248. Citroen M, Collymore A, Cooke P, Dawoe T, Daza R, Mellersh CS, Boursnell ME, Pettitt L, Ryder EJ, Holmes

The Journal of Animal Genetics (2014) 42, 79–89 87 MIYADERA

NG, Grafham D, Forman OP, Sampson J, Barnett KC, Petersen-Jones SM, Entz DD, Sargan DR (1999) cGMP Blanton S, Binns MM, Vaudin M (2006) Canine phosphodiesterase-α mutation causes progressive RPGRIP1 mutation establishes cone-rod dystrophy in retinal atrophy in the cardigan Welsh corgi dog. miniature longhaired dachshunds as a homologue of Investigative Ophthalmology & Visual Science 40, human Leber congenital amaurosis. Genomics 88, 293- 1637-1644. 301. Roberts S (1969) The collie eye anomaly. Journal of the Mellersh C. DNA testing and domestic dogs (2012) American Veterinary Medical Association 155, 859-878. Mammalian Genome 23(1-2):109-23. Sidjanin DJ, Lowe JK, McElwee JL, Milne BS, Phippen Miyadera K, Kato K, Aguirre-Hernandez J, Tokuriki T, TM, Sargan DR, Aguirre GD, Acland GM, Ostrander Morimoto K, Busse C, Barnett K, Holmes N, Ogawa H, EA (2002) Canine CNGB3 mutations establish cone Sasaki N, Mellersh CS, Sargan DR (2009) Phenotypic degeneration as orthologous to the human variation and genotype-phenotype discordance in canine achromatopsia locus ACHM3. Human Molecular cone-rod dystrophy with an RPGRIP1 mutation. Genetics 11, 1823-1833. Molecular Vision 15, 2287-2305. Stone EM (2007) Leber congenital amaurosis - a model for Miyadera K, Acland GM, Aguirre GD (2012a) Genetic and efficient genetic testing of heterogeneous disorders: phenotypic variations of inherited retinal diseases in LXIV Edward Jackson Memorial Lecture. American dogs: the power of within- and across-breed studies. Journal of Ophthalmology 144, 791-811. Mammalian Genome 23(1-2):40-61. Suber ML, Pittler SJ, Qin N, Wright GC, Holcombe V, Lee Miyadera K, Kato K, Boursnell M, Mellersh CS, Sargan DR RH, Craft CM, Lolley RN, Baehr W, Hurwitz RL (2012b) Genome-wide association study in (1993) Irish setter dogs affected with rod/cone dysplasia RPGRIP1(-/-) dogs identifies a modifier locus that contain a nonsense mutation in the rod cGMP determines the onset of retinal degeneration. phosphodiesterase ß-subunit gene. Proceedings National Mammalian Genome. 23(1-2):212-23. Acadademy of Sciences, USA 90, 3968-3972. Narfström K, Katz ML, Bragadottir R, Seeliger M, Sutter NB, Eberle MA, Parker HG, Pullar BJ, Kirkness EF, Boulanger A, Redmond TM, Caro L, Lai C-M, Rakoczy Kruglyak L, Ostrander EA (2004) Extensive and breed- PE (2003) Functional and structural recovery of the specific linkage disequilibrium in Canis familiaris. retina after gene therapy in the RPE65 null mutation Genome Research 14, 2388-2396. dog. Investigative Ophthalmology & Visual Science 44, Veske A, Nilsson SEG, Narfström K, Gal A (1999) Retinal 1663-1672 dystrophy of Swedish briard/briard-beagle dogs is due Narfstrom K, Seeliger M, Lai CM, Vaegan, Katz M, to a 4-bp deletion in RPE65. Genomics 57, 57-61. Rakoczy EP, Reme C (2008) Morphological aspects Wiik AC, Wade C, Biagi T, Ropstad EO, Bjerkas E, related to long-term functional improvement of the Lindblad-Toh K, Lingaas F (2008) A deletion in retina in the 4 years following rAAV-mediated gene nephronophthisis 4 (NPHP4) is associated with transfer in the RPE65 null mutation dog. Advances in recessive cone-rod dystrophy in standard wire-haired Experimental Medicine and Biology, 613, 139-146. dachshund. Genome Res 18(9):1415-21. Narfström K, Wrigstad A, Nilsson SEG (1989) The Briard Winkler PA, Ekenstedt KJ, Occelli LM, Frattaroli AV, Bartoe dog: a new animal model of congenital stationary night JT, Venta PJ, Petersen-Jones SM (2013) A large animal blindness. British Journal of Ophthalmology 73, 750- model for CNGB1 autosomal recessive retinitis 756. pigmentosa. PLoS One. 2013 Aug 19;8(8):e72229. Parker HG, Kukekova AV, Akey DT, Goldstein O, Kirkness Zangerl B, Goldstein O, Philp AR, Lindauer SJ, Pearce- EF, Baysac KC, Mosher DS, Aguirre GD, Acland GM, Kelling SE, Mullins RF, Graphodatsky AS, Ripoll D, Ostrander EA (2007) Breed relationships facilitate fine- Felix JS, Stone EM, Acland GM, Aguirre GD (2006) mapping studies: a 7.8-kb deletion cosegregates with Identical mutation in a novel retinal gene causes Collie eye anomaly across multiple dog breeds. Genome progressive rod-cone degeneration in dogs and retinitis Research 17, 1562-1571. pigmentosa in humans. Genomics 88, 551-563.

The Journal of Animal Genetics (2014) 42, 79–89 88 Inherited retinal diseases in dogs

Zangerl B, Wickstrom K, Slavik J, Lindauer SJ, Ahonen S, congenital amaurosis: detection of modifier alleles. Schelling C, Lohi H, Guziewicz KE, Aguirre GD (2010) Investigative Ophthalmology & Visual Science 46, Assessment of canine BEST1 variations identifies new 3052-3059. mutations and establishes an independent Zhang Q, Acland GM, Wu WX, Johnson JL, Pearce-Kelling bestrophinopathy model (CMR3). Molecular Vision 16, S, Tulloch B, Vervoort R, Wright AF, Aguirre GD 2791-2804. (2002) Different RPGR exon ORF15 mutations in AI, Perrault I, Preising MN, Lorenz B, Kaplan J, Cremers Canids provide insights into photoreceptor cell FP, Maumenee I, Koenekoop RK, Allikmets R (2005) degeneration. Human Molecular Genetics 11, 993-1003. Genotyping microarray (disease chip) for Leber

The Journal of Animal Genetics (2014) 42, 79–89 89