Inherited disorders of hemostasis in dogs and cats.

Inherited disorders of hemostasis encompass abnormalities in primary hemostasis, coagulation, and fibrinolysis resulting from genetic mutations. There is significant variation in the phenotype expressed ranging from life limiting to the absence of overt clinical signs. Von Willebrand disease is the most common primary hemostatic disorder in dogs, and hemophilia A is the most common coagulation factor disorder. The diagnosis of inherited bleeding disorders is made by functional and/or quantitative evaluation. Genetic testing has added to the knowledge base, allowing prevention through targeted breeding. Avoidance of trauma and injury is paramount in the prevention of bleeding in animals diagnosed with inherited hemostatic disorders. Current therapeutic options include platelet transfusions, broad replacement of coagulation factors (e.g., plasma), targeted factor replacement (e.g., cryoprecipitate), antifibrinolytic agents and specific factor replacement, and treatment of the symptoms (i.e., bleeding) with blood transfusions.

Hereditary factor VII deficiency in the Alaskan Klee Kai dog.

BACKGROUND: Hereditary factor VII (FVII) deficiency is characterized as a mild bleeding disorder in Beagles, caused by a missense mutation in exon 5 of the FVII gene. An Alaskan Klee Kai dog with severe bleeding after trauma was diagnosed with FVII deficiency based on coagulation testing. Molecular analyses were undertaken to identify the genetic basis of the defect in this breed. HYPOTHESIS: FVII deficiency in Alaskan Klee Kai dogs is caused by a mutation in the FVII gene. ANIMALS: Eighteen client-owned Alaskan Klee Kai. METHODS: Coagulation screening tests and factor assays were performed to characterize the coagulopathy. All coding regions of the propositus' FVII gene were sequenced. Amplification of exon 5, sequencing, and Mnl I restriction digest experiments were performed to screen for a point mutation in the remaining 17 dogs. RESULTS: FVII deficiency was diagnosed in 6 dogs with a median FVII activity (FVII: C) of 5% (reference range, 50 150%). All FVII-deficient Alaskan Klee Kai were homozygous for the same mutation as FVII-deficient Beagles (ie, a G to A transition), resulting in substitution of glycine 96 by glutamic acid. An overlap in the FVII: C values obtained from heterozygote and wild-type dogs precluded accurate detection of carriers without genetic screening. CONCLUSIONS AND CLINICAL IMPORTANCE: FVII deficiency may be associated with a bleeding tendency and should be considered in Alaskan Klee Kai dogs with prolonged prothrombin times. Plasma FVII: C accurately identifies affected dogs, but deoxyribonucleic acid testing is required for identification of carriers.

Defective gamma-glutamyl carboxylase activity and bleeding in Rambouillet sheep.

A flock of Rambouillet sheep was examined because of increased lamb mortality caused by ineffective hemostasis at parturition. Neonatal-affected lambs presented with inadequate hemostasis at the umbilicus, pale mucus membranes, and markedly prolonged activated clotting time. Affected lambs had consistently prolonged 1-stage prothrombin times and activated partial thromboplastin times that supported a defect in the common pathway or defects in both the intrinsic and extrinsic pathway of the coagulation cascade. Decreased activity of vitamin K-dependent procoagulant factors II, VII, IX, and X in male and female lambs suggested either a defect of the hepatic enzyme gamma-glutamyl carboxylase, or vitamin K(1) 2,3 epoxide reductase. Affected lamb hepatic gamma-glutamyl carboxylase activity was markedly decreased compared with that of age- and sex-matched control lambs, while vitamin K(1) 2,3 epoxide reductase and glucose-6-phosphatase activities were similar between an affected and normal lamb. Subcutaneous vitamin K(1) supplementation did not increase vitamin K-dependent procoagulant factor activities in 3 lambs administered vitamin K(1) daily. These data confirm defective gamma-glutamyl carboxylase activity as the cause of impaired coagulation of sheep in this flock. This flock represents the only viable animal model of hereditarily defective gamma-glutamyl carboxylase activity.

Truncated gamma-glutamyl carboxylase in rambouillet sheep.

A flock of Rambouillet sheep was examined because of increased lamb mortality due to ineffective hemostasis at parturition. Decreased activities of coagulation factors II, VII, IX, and X, and severely reduced hepatic gamma-glutamyl carboxylase activity with adequate vitamin K 2,3 epoxide reductase activity was determined.(1,)(21) Parenteral vitamin K(1) supplementation did not improve vitamin K-dependent coagulation factor activities in 3 affected lambs. Affected lamb gamma-glutamyl carboxylase deoxyribonucleic acid was sequenced, and 4 single nucleotide polymorphisms (SNPs 2-5) of the gamma-glutamyl carboxylase gene were identified. Single nucleotide polymorphism-4 results in an arginine to stop codon (UGA) substitution, which prematurely terminates the peptide at residue 686 (R686Stop). This genotype (GATT/GATT) has a strong association with the coagulopathy observed in clinically affected lambs, P < 0.001. The frequency of SNP-3 in exon 11 (R486H) within the MARC 1.1 database is high in the US sheep population overall. Gamma-glutamyl carboxylase activity in hepatic microsomes from a SNP-3 homozygous lamb lacking the SNP-4 mutation (GACC/GACC) was similar to control sheep homozygous for arginine at 486 and also lacking SNP-4 (TGCC/TGCC), indicating that the R486H does not measurably impact gamma-glutamyl carboxylase activity. The remaining two SNPs (2 and 5) are located within non-coding intron sequences. These 4 SNPs allowed for determining the genotype associated with the observed fatal coagulopathy. Screening for the premature truncation (SNP-4) based on the presence of a Bbv I restriction site in clinically normal lambs but not in the homozygous affected lambs allows for detection of the heterozygous state (GATT/GACC), because carrier animals are clinically normal.