Hemophilia B was first diagnosed in a Drahthaar in the United States in 1989. Since that time, approximately 20 affected males have been identified in the United States and Canada. The defect spans more than seven generations and can be traced back to dogs born and bred in Germany. The propagation of Hemophilia B in North America has been prevented, for the most part, by screening males to confirm they have normal coagulation Factor IX values. Carrier females, however, often have normal Factor IX values and cannot be directly diagnosed using Factor IX assays. Through research at Cornell's Comparative Coagulation Laboratory and the James A. Baker Institute, a new screening test has been developed to accurately identify Hemophilia B carrier females.

DNA Analyses for Hemophilia B Carrier Detection

Carrier detection is based on a direct DNA test. DNA is isolated from a blood sample and a specific portion of the Factor IX gene is then amplified and scored to detect the presence (or absence) of a unique Factor IX mutation. Hemophilia B carrier females have one copy of the mutant sequence and one copy of the normal Factor IX gene sequence. Clear females have two copies of the normal Factor IX gene sequence. DNA analysis can differentiate affected males from clear males, however coagulation Factor IX assays can accurately (and more rapidly) define a male's genetic status.

Summary of Research Findings

The carrier detection test is based on results of research sponsored initially by the VDD-Group North America and later funded by The Morris Animal Foundation. The cooperation and participation of more than twenty owners and breeders were crucial for the project's success. In this study, DNA was isolated from clear and Hemophilia B affected males and the Factor IX gene sequence was compared. Aberrant DNA sequence, referred to as an "insertion mutation" was found in the hemophilic males' Factor IX gene. The gene insertion appears to impair Factor IX protein production. A screening test to detect this mutation was developed, based on amplification of a specific portion of the Factor IX gene. Using this screening test, the Factor IX mutation was found exclusively in affected males and obligate carrier females, and was confirmed to segregate (or track) with Hemophilia B through a 5-generation pedigree. A complete description of this study is published in Mammalian Genome 2003;14:788-795.

Screening to Prevent Propagation of Hemophilia B

Males

Coagulation Factor IX assays are rapid and accurate screening tests for Hemophilia B in males. Males having normal Factor IX activities (> 50%) are not at risk for expressing or transmitting Hemophilia B. Males affected with Hemophilia B should not be used for breeding.

Females

All dams and daughters of hemophilic males are obligate carriers. Each daughter of a carrier dam has a 50% chance of being a carrier. The mutation detection test for Hemophilia B provides a specific means for determining whether a suspect or unknown status female is a carrier of Hemophilia B. Carrier females can be safely spayed, with no risk of abnormal bleeding due to Factor IX deficiency.

Testing Information

We now offer a direct DNA test for Hemophilia B carrier detection in German wirehaired pointers, a breed also known as Deutsch Drahthaar. This test identifies the presence (or absence) of a specific Factor IX mutation associated with Hemophilia B in this breed. This test is ONLY valid for Hemophilia B in German Wirehaired Ponters.

Sample Requirements

• Submit 3.0 to 4.0 ml of EDTA whole blood (purple top tube), shipped on cold packs for overnight delivery. Do not freeze whole blood.
• Registered name, number, and pedigree must be included with each submission.

Turnaround time for the DNA test is 1 to 2 weeks.

Frequently Asked Questions

What is Hemophilia B?

Hemophilia B is an inherited bleeding disorder caused by specific deficiency of coagulation Factor IX (Factor 9). In addition to Deutsch Drahthaar, Hemophilia B has been identified in more than 25 different breeds and in mixed breed dogs.

What are the clinical signs of hemophilia?

Severely affected dogs have recurrent and potentially fatal bleeds into chest, abdomen, joints, or muscles. Hemophilia B in Deutsch Drahthaar, however is relatively mild. Affected dogs have shown signs of lameness and swollen joints after strenuous exercise, prolonged bleeding from minor wounds, and hemorrhagic complications after surgery. Although Hemophilia B impacts on quality of life and performance, virtually all affected dogs survive to adulthood.

What is the inheritance pattern of Hemophilia B?

Hemophilia B is a sex-linked, recessive trait. The Factor IX gene is carried on the X chromosome. All males (XY) have a single X chromosome, inherited from their dam. If that X chromosome carries a mutant gene, the male is affected with hemophilia. All females (XX) inherit one X-chromosome from dam and one from sire. If a female inherits a mutant gene, from either parent, she is a carrier of hemophilia. Carrier females appear clinically normal and do NOT express a bleeding tendency.

Hemophilia can be transmitted by an affected sire or carrier dam as follows:

How is hemophilia diagnosed?

Affected dogs are accurately diagnosed by directly measuring blood levels of Factor IX. Severely affected dogs have less than 2% Factor IX. Hemophilic Drahthaars have values of approximately 5 to 15% Factor IX. Normal Factor IX is greater than 50%. Carrier females often have normal values of Factor IX.

What is the mutation detection test for Hemophilia B?

This direct DNA test defines the presence (or absence) of a specific mutation in the Factor IX gene. The test is performed by isolating DNA from a blood sample and then amplifying the region of the Factor IX gene that contains a mutation associated with Hemophilia B in Drahthaar. Carrier females have one normal Factor IX gene and one mutant gene. Clear females have two normal Factor IX genes.

What is the difference between a Factor IX assay and the mutation detection test?

Factor IX assay:

• A specific measure of the blood protein, coagulation Factor IX. The test must be performed on blood drawn in citrate anticoagulant and processed to separate plasma. Factor IX analysis is the definitive test for diagnosing Hemophilia B. Affected dogs have Factor IX values below 20%.

Mutation test:

• An analysis of a specific region of the Factor IX gene known to contain a mutation in Hemophilia B-affected and carrier Deutsch Drahthaar. The Hemophilia B mutation detection test is NOT a parentage test and will NOT define a dog's status for von Willebrand's disease.

Which dogs should be evaluated with the mutation detection test?

Females:

• The DNA test for mutation detection is the only accurate Hemophilia B carrier detection test for individual females in use or under consideration for breeding. Carrier females often have normal Factor IX values.

Males:

• Blood samples for Factor IX assay should be drawn in citrate anticoagulant and centrifuged to separate plasma from cells. The mutation detection test requires submission of 3.0 mL EDTA blood.

How do I submit samples for Hemophilia B screening?

Females:

• The mutation detection test requires submission of 3.0-mL whole blood in EDTA anticoagulant (purple top tube).

Males:

• A male's status can be directly defined with a Factor IX assay, however the mutation detection test will accurately differentiate affected from clear males if Factor IX assays are not performed.

Detailed sampling instructions are available from the Comparative Coagulation Section (607-275-0622; sample submission webpage).

What are the costs and test turnaround times for Hemophilia B screening?

Mutation detection test:

• The cost for the mutation detection (DNA) test is $121.25 per sample. The analyses will be performed biweekly (every other week) with results reported out within 1 to 2 weeks of sample receipt.

Factor IX assay:

• The cost for coagulation Factor IX analysis alone is $15.50. The Factor IX assay is performed daily, with results reported out within 24 hours of sample receipt.

Where can I learn more about canine Hemophilia B?

Please call the Comparative Coagulation Section laboratory at 607-275-0622 for information on testing, or any other questions on bleeding disorders. Additional information is available in the following journal articles:

• Dodds WJ, Moynihan AC, Fisher TM, and Trauner DB. 1981. The frequencies of inherited blood and eye diseases as determined by genetic screening programs. J Am Anim Hosp Assoc, 17:697-704.
• Brooks M. Hereditary Bleeding Disorders in Dogs and Cats. Veterinary Medicine June 1999; 94:555-564.
• Brooks M and Sargan D. Genetic Aspects of Disease in Dogs. In: Sampson J. and Ruvinsky, A. (eds). The Genetics of the Dog. Wallingford, UK, CABI Publishing, 2001;191-266.
• Brooks MB, Gu W, Barnas JL, Ray J, Ray K. A Line 1 insertion in the factor IX gene segregates with mild hemophilia B in dogs. Mammalian Genome 2003;14:788-795.