Keiko Miyadera

Despite increased recognition of caudal vertebral anomalies in the domestic dog (Canis lupus familiaris), studies describing tail deformities remain limited. To address this gap in the literature, this study aimed to identify and classify the caudal vertebral anomaly phenotypes in a pedigree of Beagles. Subjects included 67 dogs (36 males and 31 females), aged eight months to eight years old (M= 38.8 ± 25.6 months). All 67 dogs were visually examined, and tails were palpated to determine if they had any kinks, bends, misalignments, or deformities in their tail prior to radiographic assessment. Radiographs of the caudal vertebrae were obtained from 53 dogs and evaluated for congenital anomalies, including block vertebrae, hemivertebrae, brachyury (very short tail), and axial deviations. Of the 53 radiographed dogs, 25 (47.2%) exhibited at least one congenital caudal vertebral anomaly, with block vertebrae being the most common finding (43.4%). Four dogs (7.6%) had mild congenital abnormalities detected radiographically that were not identified during physical examination. Based on pedigree structure, an autosomal recessive trait is suspected. These findings demonstrate a high prevalence of caudal vertebral anomalies within this pedigree of Beagles and emphasize the importance of radiographic evaluation for accurate identification and phenotypic classification.

Objective: To characterize the signalment and clinical presentation of glaucoma in pet rabbits. Animal Studied: Client‐owned pet rabbits ( n = 222) referred to an exotic specialty animal hospital for ophthalmic examination between 2007 and 2023. Procedure: Medical records were retrospectively reviewed for rabbits diagnosed with glaucoma, to evaluate clinical findings and treatments. In addition to routine ophthalmic examination, gonioscopy and Encephalitozoon cuniculi serologic testing were performed when indicated. Results: Of 222 rabbits examined, 63 (28.4%) were diagnosed with glaucoma of which 33/63 (52.4%) were categorized as primary glaucoma and 27/63 (42.9%) as secondary glaucoma. Three other rabbits (4.8%) presented with unilateral secondary glaucoma with primary glaucoma risk in the fellow eye (mixed‐risk glaucoma). The mean age at diagnosis was 4.4 ± 2.8 years for primary and 10.0 ± 5.3 years for secondary glaucomas. Gonioscopy was performed in 23/33 (69.7%) of rabbits in the primary glaucoma group revealing a closed iridocorneal angle in 16/23 (69.6%). Median follow‐up was 707 days [IQR 126–1299] for primary and 59 days [IQR 1–1623] for secondary glaucomas. Medical management involved various topical antiglaucoma medications, with treatment regimens adjusted and often progressing to multi‐drug therapy. Bilateral glaucoma was ultimately documented in 75.8% (25/33) of primary and 29.6% (8/27) of secondary glaucomas. The most common underlying ocular condition associated with secondary glaucoma was suspected to be E. cuniculi infection. Conclusions: Both primary and secondary glaucomas are prevalent among pet rabbits in the Japanese population. Further studies are needed into the possible genetic factors underlying the development of glaucoma in rabbits.

Objective: To identify commonly presented dog breeds and potentially heritable ophthalmic diseases encountered by veterinarians practicing ophthalmology in Japan. Methods: A survey was distributed through the Japanese Society of Comparative and Veterinary Ophthalmology. Respondents reported frequently presented breeds for ophthalmic complaints, common ocular diseases by breed, and utilization of diagnostic modalities, including screening eye examinations, gonioscopy, electroretinography (ERG), optical coherence tomography (OCT), and DNA testing. Results: A total of 105 responses from veterinarians providing ophthalmologic service exclusively or alongside or as part of primary care were analyzed. The most frequently reported breeds were Toy Poodles ( n = 99), Shiba Inus ( n = 67), Shih Tzus ( n = 44), Chihuahuas ( n = 41), Miniature Dachshunds ( n = 27), and French Bulldogs ( n = 19), differing somewhat from the current most popular dogs according to the Japanese Kennel Club. Cataracts were reported across most popular breeds. Progressive retinal atrophy (PRA) was prevalent in Miniature Dachshunds and Toy Poodles, glaucoma in Shiba Inus, ocular surface diseases in Shih Tzus, and corneal endothelial dystrophy in Chihuahuas. Screening eye examinations are being performed by 14% of clinicians for puppies and 25% for adult dogs, most frequently by specialists. Gonioscopy and ERG were each utilized by 69% of respondents, OCT by 23%, and DNA testing by 31% through providers offering variable tests and formats. Conclusions: Commonly encountered breeds and heritable ophthalmic diseases were characterized, highlighting possible focus of future clinical and molecular research. Implementation of standardized screening, advanced diagnostics, and genetic testing may improve control of these diseases in Japan's canine population.

Objective: Cone‐rod dystrophy (cord1) is a form of progressive retinal atrophy. It is linked to an RPGRIP1 genetic variant which is the third most common canine disease variant thus far. While the variant affects various breeds, it is highly prevalent in English Springer Spaniels (ESSs). Yet its clinical and pathological implications remain equivocal. Herein, we study the retinal phenotype in ESSs genetically affected with the RPGRIP1 variant. Animal Studied: Over 4 years, 494 ESSs (123 affected) were enrolled. Procedure(s): Owner‐perceived vision was collected via a questionnaire. Ophthalmic examination included fundus photography. In selected ESSs, retinal function and structure were assessed using electroretinography (ERG, 148 dogs) and optical coherence tomography (OCT, 4 dogs). Results: Ophthalmoscopic changes included peripheral hypo‐reflective lesions often with distinct borders progressing centripetally culminating in generalized retinal atrophy. Cross‐sectional study revealed declining photopic ERG amplitudes with age in the affected group but not in controls. OCT indicated progressive photoreceptor loss. Despite ophthalmoscopic, ERG, or OCT abnormalities, most affected dogs were not visually impaired per their owners. In a fraction of afflicted ESSs, vision/globe‐threatening complications were documented including cataracts, lens luxation, and glaucoma. Conclusions: In ESSs, the RPGRIP1 variant is associated with insidious pathology with delayed‐onset visual defects. The subtle phenotype without apparent visual deficit until the final years of life, if at all, may have caused underdiagnosis of cord1. Still, DNA testing remains informative, and ERG and OCT indicate progressive pathology. Peripheral fundus examination and photopic ERG are particularly useful for early detection and monitoring of cord1.

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.

Editorial: Primary cilia as therapeutic targets

The primary cilium is a single immotile microtubule-based organelle that protrudes into the extracellular space. Malformations and dysfunctions of the cilia have been associated with various forms of syndromic and non-syndromic diseases, termed ciliopathies. The primary cilium is therefore gaining attention due to its potential as a therapeutic target. In this review, we examine ciliary receptors, ciliogenesis, and ciliary trafficking as possible therapeutic targets. We first discuss the mechanisms of selective distribution, signal transduction, and physiological roles of ciliary receptors. Next, pathways that regulate ciliogenesis, specifically the Aurora A kinase, mammalian target of rapamycin, and ubiquitin-proteasome pathways are examined as therapeutic targets to regulate ciliogenesis. Then, in the photoreceptors, the mechanism of ciliary trafficking which takes place at the transition zone involving the ciliary membrane proteins is reviewed. Finally, some of the current therapeutic advancements highlighting the role of large animal models of photoreceptor ciliopathy are discussed.

Photoreceptors possess a highly specialized primary cilium containing expanded ciliary membrane discs called the outer segment. The photoreceptor cilium is essential for the maintenance of the outer segment, and pathogenic variants in more than 50 cilia-related genes have been identified as causing non-syndromic inherited retinal diseases in patients. The retinitis pigmentosa GTPase regulator interacting protein 1 (RPGRIP1) is a structural protein localized to the photoreceptor cilium and biallelic RPGRIP1 variants have been associated with non-syndromic human inherited retinal diseases. In a canine cone-rod dystrophy model, a naturally occurring 44-bp exonic insertion in RPGRIP1 (RPGRIP1^ins44/ins44) is the primary disease locus while an additional homozygous variant in MAP9 (microtubule associated protein 9) (MAP9^aff/aff) acts as a modifier associated with early disease onset. MAP9 was originally identified as a microtubule-binding protein stabilizing microtubule structure during both mitosis and interphase in human cell lines. However, the roles of MAP9 in primary cilia, including photoreceptor neurosensory cilia, have not been well understood. Hence, we characterized the pathogenic phenotypes associated with homozygous MAP9 variant, and investigated the molecular function of MAP9 in primary cilia using the RPGRIP1-associated oligogenic canine cone-rod dystrophy model as well as cultured cells. Both functionally and structurally, the RPGRIP1^ins44/ins44MAP9^aff/aff retina exhibited progressive cone photoreceptor degeneration starting earlier than the retina affected by RPGRIP1^ins44/ins44 alone. Based on immunostaining of canine retinal sections and cultured cells, we found that MAP9 is prominently localized in the basal body of primary cilia and played an important role in maintaining the structure of ciliary microtubule axoneme. These findings suggest that the affected MAP9, together with mutant RPGRIP1, is deprived of critical roles in cilia organization and maintenance resulting in altered cilia structure and function giving rise to early onset and accelerated disease progression in the RPGRIP1^ins44/ins44MAP9^aff/aff double homozygote cone-rod dystrophy canine model.

Canine RPGRIP1-cone-rod dystrophy (CRD), a model for human inherited retinal diseases (IRDs), was originally identified as autosomal recessive early-onset blindness. However, later studies revealed extensive phenotypic variability among RPGRIP1 mutants. This led to the identification of a homozygous MAP9 variant as a modifier associated with early-onset disease. Based on further phenotypic variation affecting cone photoreceptor function, we report mapping of L3 as an additional modifier locus, within a 4.1-Mb locus on canine chromosome 30. We establish the natural disease history of RPGRIP1-CRD based on up to nine-year long-term functional and structural retinal data from 58 dogs including 44 RPGRIP1 mutants grouped according to the modifier status. RPGRIP1 mutants affected by both MAP9 and L3 modifiers exhibited the most severe phenotypes with rapid disease progression. MAP9 alone was found to act as an overall accelerator of rod and cone diseases, while L3 had a cone-specific effect. Ultrastructural analysis of photoreceptors revealed varying degrees of rod and cone damage, while the connecting cilia appeared structurally preserved in all groups. We conclude that RPGRIP1-CRD is an oligogenic disease with at least three loci contributing to the pathogenesis. While the RPGRIP1 variant is required for developing the disease, MAP9 and L3 modifiers exacerbate the phenotype, individually and cumulatively. Oligogenic canine RPGRIP1-CRD illustrates the impact of multiple genetic modifiers on disease phenotype and thus has the potential to reveal new targets for broad-spectrum therapies for oligogenic or polygenic forms of human IRDs.