Identification of a Novel Mutation in the SERPINE1 Gene Causing Clinical Hyperfibrinolysis in English Springer Spaniel Dogs

Background: A 7-month-old female spayed English Springer Spaniel (ESS) was evaluated for spontaneous hemoperitoneum. Hyperfibrinolysis was identified on thromboelastography. Hypothesis/Objectives: To identify a genetic mutation causing congenital hyperfibrinolysis in the proband and evaluate the prevalence of the mutation in the ESS breed. Animals: Client-owned ESS with hemorrhage and a non-affected littermate. Samples of DNA from 3 ESS, 1 Welsh Springer Spaniel (WSS) with unexplained hemorrhage, and 199 ESS with no history of hemorrhage. Methods: Whole genome sequencing (WGS) of the proband with variant filtering against an in-house WGS database of 671 presumably unaffected dogs identified a deleterious variant of SERPINE1 unique to the proband, which encodes for plasminogen activator inhibitor 1 (PAI-1). SERPINE1 was genotyped in the remaining animal population by Sanger sequencing or a Taqman assay. Liquid chromatography tandem mass spectrometry (LC–MS/MS) was performed on platelet pellets from the proband, a littermate, and three unrelated healthy ESS. Results: Whole genome sequencing of the proband identified a unique homozygous insertion at chr6:8640592 in exon 1 of SERPINE1, which is predicted to cause a premature stop codon. The unaffected littermate was heterozygous for the mutation. Two unrelated ESS and 1 WSS with post-operative hemorrhage were homozygous for the mutation. Absence of PAI-1 in the proband's platelets was documented using LC–MS/MS. Conclusions and Clinical Importance: This novel mutation in SERPINE1 is associated with the absence of the PAI-1 protein in platelets and might cause hemorrhage because of hyperfibrinolysis in ESS and related breeds.