Information about DNA testing for Hereditary Necrotising Myelopathy (ENM)   The DNA test for ENM.
Since many years the VHNK was aware of Hereditary Necrotising Myelopathy in our kooiker breed. In the beginning this terrible disease was also named kooikerparalysis.  The manifestation of ENM symptoms with affected dogs starts at an early age, mostly before the first birthday. Symptoms of paralysation are most likely painless for the dogs but will be getting worse rather quickly and most dogs will be euthanized before they reach the age of 2. For owner as well the dog this is a terrible experience.
Inheritance of ENM. Based on a retrospective study conducted in 1992 made by Dr. Paul Mandigers (Faculty of Veterinary Medicine, Utrecht University) the assumtion was made that in all probability ENM has an autosomal singular recessive inheritance. Dogs can only be diagnosed with ENM definitely when this is proven by autopsy after death. This research will take place at the Faculty of Veterinarian Medicine, Utrecht University. In this way a lot of DNA material was collected in the past years. In addition, all breeding dogs have to be tested for VWD since 1998. With this test, owners declare that the DNA material from the test may be stored and can be used for future scientific research. Nowadays the Nederlandse Kooikerhondje is a breed with an extensive DNA database.
The breeding rules of the VHNK are draughted to reduce hereditary diseases as much as possible. Because dogs affected by ENM will never be used for breeding, the current breeding standard only regulates the exclusion of ENM carriers for breeding. Parent dogs can only be declared a carrier when they have ENM affected offspring wich have been diagnosed by autopsy. While the DNA test was not available, the computer program Dogbase provided the possibility to calculate the probabilty of being ENM carrier. Several breeders, most often owners of stud dogs, have asked for calculations of specific combinations.
Although the 1992 research was indicative of a simple ENM inheritance, only recently a practical DNA analysis became availlable. This is partly because the analysis techniques have advanced, but also because a minimal number of affected dogs is necessary for such an analysis. In recent years, Paul Mandigers collected blood samples from all ENM affected dogs he saw for DNA isolation. This, together with the samples from ENM dogs from Germany (established thanks to the good cooperation of breeders and VHNK and DCK), provided sufficient genetic material for the analysis.
Recently the lab of Dr. Peter Leegwater (Faculty of Veterinary Medicine, Utrecht University) searched for the ENM gene with the new technology. For this research, Dr. Peter Leegwater and Dr. Paul Mandigers managed to secure a grant from the European Lupa project. The search was successful. Soon a chromosome was found with all affected dogs that was different from the control animals. The gene itself is harder to find. Eventually it was possible to identify two variants which together are always found in the immediate vicinity of the putative ENM gene. More control tests with parents (who are both carriers) and grandparents (that may be carriers and free animals) were performed, which were positive. Work will continue for the exact identification of the mutation. Meanwhile, a practical test is available. By designating these two variants it is now possible to identify a ENM carrier with a high degree of probability. The research at the Faculty of Veterinary Medicine has already shown our population contains a large number of ENM carriers, even among breeding dogs.
Measures by the VHNK During the project it appeared that a number of animals used for research, whose DNA was obtained from previous (VWD) research, are carrier of the ENM gene. The owners of these dogs do not pay for this test and are personally informed by the VHNK about the test results of their dog. A list of ENM carriers and free tested dogs will be published in the next club magazine. With the availability of the test ENM it is now possible for dogs, which in the past would have been excluded from breeding, to be tested and preserved for breeding.
Regulating ENM ENM carriers can now be identified by DNA test. From a combination of a carrier and a free tested dog, no ENM affected dogs will be born. Only when two carriers are combined, statistically ¼ affected animals are born. The presumption is that 15% to 20% of the Dutch Kooikerhondje population are carrier of the ENM gene. This is such a high number of breeding material the decision was made not to exclude ENM carriers for breeding.
Of course it is important to regulate breeding with ENM carriers. We propose to add the following regulations into the breeding standard:
All dogs used for breeding have to be tested for carriage of ENM. Allowed for breeding are the following combinations: Free x Free Free x Carrier The combination carrier x carrier is not allowed.
This adjustment is effective upon publication in the club magazine.
At the General Assembly of 2013, the Board will present a detailed proposal for adaptation of the breeding standard. Until then, Dutch breeding policy will be in accordance with above mentioned regulations. We strongly request our cooperating foreign Kooiker clubs to implement the same regimen.