Background:
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 Pointers.
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.
Cost per test is $100.00.
Group members should feel free to call the Coagulation Laboratory (607-275-0622) for any questions on Hemophilia B or other hereditary bleeding disorders.
This article appeared in Drahthaar News, March/April 2003. The information was taken from the Cornell University College of Veterinary Medicine Comparative Coagulation Section website. Further information about blood disorders in the DD can be found by visiting this site at http://web.vet.cornell.edu/public/coaglab/hembgwp.htm.
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