Characterization of the Mutations Causing Hemophilia B in 2 Domestic Cats

Standardization of Coagulation Factor V Reference Intervals, Prothrombin Time, and Activated Partial Thromboplastin Time in Mice for Use in Factor V Deficiency Pathological Models

Factor V together with activated factor X forms the prothrombinase complex, which transforms prothrombin into thrombin. The Mus musculus species is characterized by very high levels of this factor and short clotting times, which hinders accurate measurements. For that reason, a detailed characterization of such parameters is indispensable. A method was designed as part of this study to provide an accurate determination and standardization of factor V levels, prothrombin time and activated partial thromboplastin time in Mus musculus. Those parameters were evaluated in a sample of 66 healthy animals using a semi-automated coagulometer and human diagnostic reagents in an attempt to determine the most appropriate time of day for the extractions. A mouse-based protocol was designed, capable of making corrections to the samples at dilutions of 1:100 for factor V and at of 1:3 for prothrombin time. The goal was to smoothen the calibration curves, which often present with steep slopes and narrow measurement ranges between one calibration point and another. It was found that the most stable period for blood sample extraction was that comprised between the first 6 h of light. No clinical differences were observed between the sexes and reference intervals were established for factor V (95.80% ± 18.14; 25.21 s ± 1.34), prothrombin time (104.31% ± 14.52; 16.85 s ± 1.32) and activated partial thromboplastin time (32.86 s ± 3.01). The results obtained are applicable to human or veterinary biomedical research, to transfusional medicine or to pathological models for diseases such as factor V deficiency.

Investigation of pathological haemorrhage in Maine Coon cats

OBJECTIVE

Afibrinogenaemic haemorrhage was previously reported in a Maine Coon cat. Two littermates subsequently died from surgical non-haemostasis, suggesting a hereditable coagulopathy.

METHODS

We prospectively recruited cats which were: a) Maine Coons with pathological haemorrhage (group 1, n=8), b) healthy familial relatives of group 1 (group 2, n=13) and c) healthy Maine Coons unrelated to groups 1 and 2 (group 3, n=12). Coagulation tests: prothrombin time, activated partial thromboplastin time and thrombin clotting time (TCT) were performed on citrated plasma along with quantification of fibrinogen. Routine haematological examination was performed on EDTA-anticoagulated blood collected contemporaneously.

RESULTS

Thirty-three blood samples were analysed. Fibrinogen concentrations were significantly reduced in groups 1 (P<0.01) and 2 (P<0.01) compared with group 3. Similarly, TCT was found to be significantly extended in group 1 (P<0.01) and group 2 (P=0.02) with respect to group 3.

CONCLUSIONS

Dysfibrinogenaemia was identified in clinical cases and their healthy relatives, suggesting that this may represent a hereditary condition of Maine Coon cats. Clinicians should be aware of the increased potential for non-haemostasis in this cat breed and consider assessing clotting function before (elective) surgery.

Genetics of equine bleeding disorders

Genetic bleeding disorders can have a profound impact on a horse's health and athletic career. As such, it is important to understand the mechanisms of these diseases and how they are diagnosed. These diseases include haemophilia A, von Willebrand disease, prekallikrein deficiency, Glanzmann's Thrombasthenia and Atypical Equine Thrombasthenia. Exercise-induced pulmonary haemorrhage also has a proposed genetic component. Genetic mutations have been identified for haemophilia A and Glanzmann's Thrombasthenia in the horse. Mutations are known for von Willebrand disease and prekallikrein deficiency in other species. In the absence of genetic tests, bleeding disorders are typically diagnosed by measuring platelet function, von Willebrand factor, and other coagulation protein levels and activities. For autosomal recessive diseases, genetic testing can prevent the breeding of two carriers.

Spontaneous thoracolumbar hematomyelia secondary to hemophilia B in a cat

Case summary

A 10-year-old neutered male domestic shorthair cat presented for evaluation of acute onset of paraplegia with loss of nociception and thoracolumbar spine hyperesthesia and no history of trauma. Activated partial thromboplastin time (aPTT) was markedly prolonged, and specific coagulation factor testing revealed a factor IX level of 4% of normal activity, confirming the presence of mild hemophilia B. Prior abnormal bleeding had occurred at the time of castration as a kitten, as well as with laceration to a toe. Advanced imaging, including computed tomography (CT) and magnetic resonance imaging (MRI) of the thoracolumbar spine, confirmed the presence of multifocal intradural and intramedullary spinal cord hemorrhage through demonstration of focal ring enhancement on CT and multifocal areas of signal void on gradient echo T2* images on MRI. Despite factor IX supplementation through the use of fresh frozen plasma transfusions and normalization of the aPTT time, the cat’s neurological status did not improve. Owing to repeated urinary tract infections, with increasing resistance to antibiotic therapy, the cat was ultimately euthanized. Post-mortem examination showed no evidence of another underlying primary pathology for the hematomyelia.

Relevance and novel information

To our knowledge, this case demonstrates the first reported occurrence of spontaneous hematomyelia secondary to hemophilia B in a cat.

DNA mutations of the cat: the good, the bad and the ugly

PRACTICAL RELEVANCE

The health of the cat is a complex interaction between its environment (nurture) and its genetics (nature). Over 70 genetic mutations (variants) have been defined in the cat, many involving diseases, structural abnormalities and clinically relevant health concerns. As more of the cat's genome is deciphered, less commonly will the term 'idiopathic' be used regarding the diagnosis of diseases and unique health conditions. State-of-the-art health care will include DNA profiling of the individual cat, and perhaps its tumor, to establish the best treatment approaches. Genetic testing and eventually whole genome sequencing should become routine diagnostics for feline health care.

GLOBAL IMPORTANCE

Cat breeds have disseminated around the world. Thus, practitioners should be aware of the breeds common to their region and the mutations found in those regional populations. Specific random-bred populations can also have defined genetic characteristics and mutations.

AUDIENCE

This review of 'the good, the bad and the ugly' DNA variants provides the current state of knowledge for genetic testing and genetic health management for cats. It is aimed at feline and general practitioners wanting to update and review the basics of genetics, what tests are available for cats and sources for genetic testing. The tables are intended to be used as references in the clinic. Practitioners with a high proportion of cat breeder clientele will especially benefit from the review.

EVIDENCE BASE

The data presented is extracted from peer-reviewed publications pertaining to mutation identification, and relevant articles concerning the heritable trait and/or disease. The author also draws upon personal experience and expertise in feline genetics.

Genetic testing in domestic cats

Varieties of genetic tests are currently available for the domestic cat that support veterinary health care, breed management, species identification, and forensic investigations. Approximately thirty-five genes contain over fifty mutations that cause feline health problems or alterations in the cat's appearance. Specific genes, such as sweet and drug receptors, have been knocked-out of Felidae during evolution and can be used along with mtDNA markers for species identification. Both STR and SNP panels differentiate cat race, breed, and individual identity, as well as gender-specific markers to determine sex of an individual. Cat genetic tests are common offerings for commercial laboratories, allowing both the veterinary clinician and the private owner to obtain DNA test results. This article will review the genetic tests for the domestic cat, and their various applications in different fields of science. Highlighted are genetic tests specific to the individual cat, which are a part of the cat's genome.

Feline genetics: clinical applications and genetic testing

DNA testing for domestic cat diseases and appearance traits is a rapidly growing asset for veterinary medicine. Approximately 33 genes contain 50 mutations that cause feline health problems or alterations in the cat's appearance. A variety of commercial laboratories can now perform cat genetic diagnostics, allowing both the veterinary clinician and the private owner to obtain DNA test results. DNA is easily obtained from a cat via a buccal swab with a standard cotton bud or cytological brush, allowing DNA samples to be easily sent to any laboratory in the world. The DNA test results identify carriers of the traits, predict the incidence of traits from breeding programs, and influence medical prognoses and treatments. An overall goal of identifying these genetic mutations is the correction of the defect via gene therapies and designer drug therapies. Thus, genetic testing is an effective preventative medicine and a potential ultimate cure. However, genetic diagnostic tests may still be novel for many veterinary practitioners and their application in the clinical setting needs to have the same scrutiny as any other diagnostic procedure. This article will review the genetic tests for the domestic cat, potential sources of error for genetic testing, and the pros and cons of DNA results in veterinary medicine. Highlighted are genetic tests specific to the individual cat, which are a part of the cat's internal genome.

A 1.5-Mb-resolution radiation hybrid map of the cat genome and comparative analysis with the canine and human genomes

We report the construction of a 1.5-Mb-resolution radiation hybrid map of the domestic cat genome. This new map includes novel microsatellite loci and markers derived from the 2X genome sequence that target previous gaps in the feline-human comparative map. Ninety-six percent of the 1793 cat markers we mapped have identifiable orthologues in the canine and human genome sequences. The updated autosomal and X-chromosome comparative maps identify 152 cat-human and 134 cat-dog homologous synteny blocks. Comparative analysis shows the marked change in chromosomal evolution in the canid lineage relative to the felid lineage since divergence from their carnivoran ancestor. The canid lineage has a 30-fold difference in the number of interchromosomal rearrangements relative to felids, while the felid lineage has primarily undergone intrachromosomal rearrangements. We have also refined the pseudoautosomal region and boundary in the cat and show that it is markedly longer than those of human or mouse. This improved RH comparative map provides a useful tool to facilitate positional cloning studies in the feline model.