Department of Veterinary Medical Sciences, University of Bologna, Bologna, Italy.
Genefast, Forlì, Italy.
PLoS One. 2019 Sep 4;14(9):e0220625. doi: 10.1371/journal.pone.0220625. eCollection 2019.
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.
遗传性出血性疾病包括血小板数量和功能异常，在多种犬种中很少发生，但可能诊断不足。犬类特有的遗传性血小板疾病为了解人类相似的血小板疾病提供了有价值的大型动物模型。已知仅 8 种不同基因中的与品种特异性疾病相关的遗传变异可导致犬类的内在血小板疾病。然而，到目前为止，许多犬种的致病遗传变异仍未知。本文介绍了 4 例可卡犬中轻重不一的出血性疾病。受影响的犬表现出血小板黏附缺陷，其特征为巨血小板增多症，血小板计数变化，类似于人类伯纳德-苏利耶综合征（BSS）。此外，通过免疫细胞化学证明缺乏功能性 GPIb-IX-V。对一只受影响的犬进行全基因组测序，并对候选基因进行目视检查，发现血小板糖蛋白 IX（GP9）基因缺失。GP9 基因编码血小板表面膜糖蛋白复合物的一个亚单位；作为血管性血友病因子的受体，在受伤后启动止血的维持。人类 GP9 中的变异与伯纳德-苏利耶综合征 C 型相关。该缺失跨越 2460 bp，包括犬染色体 20 上犬 GP9 基因的单个编码外显子的重要部分。该变异导致移码和提前终止密码子，预测截短近三分之二的编码蛋白。基于 PCR 的基因分型证实了隐性遗传。受影响犬的纯合变异基因型在 98 只对照可卡犬中未发生。因此，得出结论，在检查的犬中，GP9 基因中的结构变异很可能是导致 BSS 表型的原因。这些发现为这一组遗传性血小板疾病提供了首个大型动物 GP9 模型，并极大地促进了可卡犬中受影响和/或正常携带者的诊断和鉴定。
