Inherited platelet disorders

Prophylactic use of a lyophilized platelet product for rhinoscopic diagnosis and treatment of sinonasal aspergillosis in a dog with a P2Y12 platelet receptor mutation

OBJECTIVE

To describe the periprocedural use of a lyophilized platelet product during rhinoscopic diagnosis and treatment of sinonasal aspergillosis in a Greater Swiss Mountain Dog with a P2Y12 platelet receptor disorder.

CASE SUMMARY

After the development of severe epistaxis, a Greater Swiss Mountain Dog was diagnosed with thrombopathia secondary to a P2Y12 receptor gene mutation. Concurrent primary nasal disease was also suspected due to persistent mucopurulent nasal discharge. One month after the initial presentation for epistaxis, the dog was readmitted for workup of nasal disease. Computed tomography of the head showed turbinate lysis and regional lymphadenopathy. Because of concern for a high risk of bleeding in a thrombopathic patient subjected to rhinoscopy and nasal biopsies, a lyophilized platelet product was administered prior to the procedure. Rhinoscopic exam revealed fungal plaques consistent with Aspergillus spp. that were later confirmed on fungal culture to be Aspergillus fumigatus. Rhinoscopic biopsies were performed as well as debridement of the fungal plaques, followed by topical administration of clotrimazole solution. Bleeding was minimal during and after the procedure, and the dog recovered uneventfully.

NEW OR UNIQUE INFORMATION PROVIDED

This is the first report of the prophylactic use of lyophilized platelets in a thrombopathic patient undergoing an invasive procedure with potential for significant hemorrhage. Minimal bleeding occurred during the procedure, suggesting that lyophilized platelets could be used for the prevention of bleeding in thrombopathic patients undergoing invasive procedures.

Case report of unilateral retrobulbar hematoma associated with von Willebrand disease in a Doberman Pinscher dog

A 5-year-old Doberman Pinscher dog was presented with sudden onset left-sided periocular bleeding following third eyelid gland replacement surgery. Left-sided exophthalmos and 360-degrees subconjunctival hemorrhage were present. The ophthalmic examination revealed blindness with absent direct and consensual pupillary light reflexes. A superficial exposure ulcerative keratitis due to exophthalmos was also present. Computed tomography (CT) revealed a large left-sided retrobulbar mass lesion surrounding the optic nerve, compatible with a retrobulbar hematoma. Due to absence of orbital fractures and no history of trauma, a coagulopathy was strongly suspected. The buccal mucosal bleeding time (BMBT) was prolonged (>4 minutes) consistent with a primary hemostatic defect in the absence of thrombocytopenia. Von Willebrand factor antigens levels were decreased (24%- Normal Range: 50%-150%). Surgical drainage of the retrobulbar hematoma was performed uneventfully thirty minutes after subcutaneous injection of desmopressine acetate, Minirin® (1 µg/kg, SC). Von Willebrand disease type I gene mutation was confirmed by PCR amplification of the DNA encoding von Willebrand factor. This case report demonstrates that hemostatic disorders, including von Willebrand Disease (vWD), are a risk factor for orbital bleeding following surgical trauma. Retrobulbar hematoma should be considered as a differential diagnosis in any dog with exophthalmos.

Platelet Function and Therapeutic Applications in Dogs: Current Status and Future Prospects

Significant progress has been made in the functional characterization of canine platelets in the last two decades. The role of canine platelets in hemostasis includes their adhesion to the subendothelium, activation, and aggregation, leading to primary clot formation at the site of injury. Studies on canine platelet function and advancements in laboratory testing have improved the diagnosis and understanding of platelet-related disorders as well as the knowledge of the mechanisms behind these diseases. This review focuses on the most recent discoveries in canine platelet structure, function, and disorders; and discusses the efficacy of various tests in the diagnosis of platelet-related disorders. With the relatively recent discovery of angiogenetic and reparative effects of growth factors found in platelets, this review also summarizes the use of canine platelet-rich plasma (PRP) alone or in association with stem cells in regenerative therapy. The characterization of proteomic and lipidomic profiles and development of platelet gene therapy in veterinary species are areas of future study with potential for major therapeutic benefits.

A large deletion in the GP9 gene in Cocker Spaniel dogs with Bernard-Soulier syndrome

Inherited bleeding disorders including abnormalities of platelet number and function rarely occur in a variety of dog breeds, but are probably underdiagnosed. Genetically characterized canine forms of platelet disorders provide valuable large animal models for understanding similar platelet disorders in people. Breed-specific disease associated genetic variants in only eight different genes are known to cause intrinsic platelet disorders in dogs. However, the causative genetic variant in many dog breeds has until now remained unknown. Four cases of a mild to severe bleeding disorder in Cocker Spaniel dogs are herein presented. The affected dogs showed a platelet adhesion defect characterized by macrothrombocytopenia with variable platelet counts resembling human Bernard-Soulier syndrome (BSS). Furthermore, the lack of functional GPIb-IX-V was demonstrated by immunocytochemistry. Whole genome sequencing of one affected dog and visual inspection of the candidate genes identified a deletion in the glycoprotein IX platelet (GP9) gene. The GP9 gene encodes a subunit of a platelet surface membrane glycoprotein complex; this functions as a receptor for von Willebrand factor, which initiates the maintenance of hemostasis after injury. Variants in human GP9 are associated with Bernard-Soulier syndrome, type C. The deletion spanned 2460 bp, and included a significant part of the single coding exon of the canine GP9 gene on dog chromosome 20. The variant results in a frameshift and premature stop codon which is predicted to truncate almost two-thirds of the encoded protein. PCR-based genotyping confirmed recessive inheritance. The homozygous variant genotype seen in affected dogs did not occur in 98 control Cocker Spaniels. Thus, it was concluded that the structural variant identified in the GP9 gene was most likely causative for the BSS-phenotype in the dogs examined. These findings provide the first large animal GP9 model for this group of inherited platelet disorders and greatly facilitate the diagnosis and identification of affected and/or normal carriers in Cocker Spaniels.

vWDI is inherited in an autosomal dominant manner with incomplete penetrance, in the Kromfohrländer breed

Background

Von Willebrand disorder type I (vWDI) is known as an inherited bleeding disorder in different dog breeds following an autosomal recessive inheritance. The Kromfohrländer is a rare dog breed with an increased incidence of unclear bleeding episodes and prolonged coagulation time during/after surgery or injuries, indicating a defect in one or more critical proteins of the coagulation cascade.

Objective

The objective of this study was to determine whether the c.7437G > A mutation in the VWF gene previously shown to cause von Willebrand disorder type I in Doberman Pinscher is also linked to this disease in the Kromfohrländer breed and to serum concentrations of vWF. Furthermore, establish a possible link between bleeding phenotype, vWF serum concentrations and VWF mutation status.

Results

Eighty-seven Kromfohrländer were genotyped for the G > A von Willebrand type I mutation. For detection of the associated mutation we used an endpoint genotyping method. We identified the G > A von Willebrand type I mutation in 80.5% of our study population. 65.5% were heterozygous (WT/MUT) and 15.0% were homozygous for the mutation (MUT/MUT). 21% of the overall study population exhibited bleeding symptoms. 45.5% of all homozygous dogs (MUT/MUT) showed bleeding symptoms. In contrast, wild-type homozygotes exhibited no bleeding symptoms, whereas 23.2% of the heterozygotes did. VWF serum concentrations varied from 28 to 137% in wild-type dogs while in heterozygous and homozygous dogs the concentration ranged from 3 to 77% and 1 to 23%, respectively (p < 0.05)

Conclusion

Based on our data, we found the G > A mutation in the VWF gene in the Kromfohrländer breed and the subsequent vWDI as the underlying cause for the bleeding episodes and delayed coagulation in heterozygous and homozygous dogs. Since both, heterozygotes and homozygotes show reduced vWF serum concentrations and exhibit to a certain percentage the vWD syndrome phenotype, we postulate that, in contrast to most other vWDI affected breeds, inheritance follows an autosomal dominant mode with incomplete penetrance.

von Willebrand disease type 1 in Doberman Pinscher dogs: genotyping and prevalence of the mutation in the Buenos Aires region, Argentina

von Willebrand disease (vWD) is the most common inherited coagulopathy in dogs, particularly in Doberman Pinschers. We developed a pyrosequencing-based assay to estimate the frequency of the c.7437G>A mutation associated with vWD type 1 in the Doberman Pinscher population of Buenos Aires, Argentina. We found a 0.41 frequency for the mutated allele, which varied significantly within families (family 1 = 0.43, family 2 = 0.58, unrelated animals = 0.35). The use of a popular founder male carrier of mutant allele A increased vWD incidence within a family and in the general population. The mode of inheritance was confirmed as autosomal dominant with incomplete penetrance. No differences were found between sexes and coat colors. Pyrosequencing was a good complement to clinical and coagulation tests for vWD type 1 diagnosis and a useful alternative for detecting the c.7437G>A mutation.

Bottlenecks and selective sweeps during domestication have increased deleterious genetic variation in dogs

Population bottlenecks, inbreeding, and artificial selection can all, in principle, influence levels of deleterious genetic variation. However, the relative importance of each of these effects on genome-wide patterns of deleterious variation remains controversial. Domestic and wild canids offer a powerful system to address the role of these factors in influencing deleterious variation because their history is dominated by known bottlenecks and intense artificial selection. Here, we assess genome-wide patterns of deleterious variation in 90 whole-genome sequences from breed dogs, village dogs, and gray wolves. We find that the ratio of amino acid changing heterozygosity to silent heterozygosity is higher in dogs than in wolves and, on average, dogs have 2-3% higher genetic load than gray wolves. Multiple lines of evidence indicate this pattern is driven by less efficient natural selection due to bottlenecks associated with domestication and breed formation, rather than recent inbreeding. Further, we find regions of the genome implicated in selective sweeps are enriched for amino acid changing variants and Mendelian disease genes. To our knowledge, these results provide the first quantitative estimates of the increased burden of deleterious variants directly associated with domestication and have important implications for selective breeding programs and the conservation of rare and endangered species. Specifically, they highlight the costs associated with selective breeding and question the practice favoring the breeding of individuals that best fit breed standards. Our results also suggest that maintaining a large population size, rather than just avoiding inbreeding, is a critical factor for preventing the accumulation of deleterious variants.