Health Topics

Degenerative Myelopathy (DM)

CREDIT: DMBerneres@yahoogroups.com / stellaflydesign.com – First published in ‘Bernese Please’ magazine of the BMDC of Canada

Degenerative Myelopathy (DM) has been around and known about for many years in many breeds but has been getting increased awareness and attention within our breed over the last few years with information coming to the fore that cases are occurring in not only more older dogs but some younger dogs as well. So, it is logical to say that DM is probably of increasing relevance in the list of things to consider when breeding Bernese Mountain Dogs. Some breeders, indeed some countries, have decided that DM is primarily a disease of the older dog so is not of great relevance to Bernese. This view may have a little validity when taken in certain contexts but try telling that to the owners of afflicted dogs.

Genetically Speaking

There is a genetic mutation involved in the incidence of DM that has been found in all affected breeds. As it is present in all dogs and is the only one identified in most cases it is sometimes just known as the DM mutation but for Bernese it is better to refer to this as SOD1A. In Bernese, and only Bernese so far, there is also a second mutation at the same location, logically referred to as SOD1B. There are other breeds with separate mutations linked to DM occurrence so we are not unique in this.

Fortunately there are genetic tests available for both of these mutations so breeders should not be taking a step into the dark. To be strictly correct the only 100% validated diagnosis is by means of cross sectional microscopic examination of the spinal cord but this can obviously only be done after death. Practically speaking, the best diagnosis of a symptomatic dog is partly by assessing the symptoms and using the DNA test to give strong supportive evidence. Many conditions will cause similar symptoms so it is about accumulating as much information as you can.

Just to be clear, these are separate tests which means two tests per dog. Each test gives three possible results, Clear, Carrier or Affected. The mode of inheritance of these mutations in breeding combinations is the straightforward autosomal recessive type known to all responsible breeders namely.

Clear to Clear can only result in clear puppies and no chance of developing the disease or any of the puppies helping to pass it on in the future. This would obviously be the ideal world option but would immediately take out around 60% of the gene pool which we can ill afford to do. We have to operate in the real world so in reality we have to work with other options as exampled below.

Clear to Carrier will result (on average) in an even mix of carriers and clears but crucially no affected or at risk dogs.

Carrier to Carrier will result (on average) in 25% clear, 50% carrier but crucially 25% affected or at risk puppies.

Carrier to Affected will result (on average) in 50% carriers and 50% affected or at risk puppies.

Affected to Affected will result in 100% of affected/at risk puppies.

Affected to Clear will result in 100% of genetic carriers but crucially no affected or at risk dogs.

Affected equals At Risk?

In the attached Bernese perspective article by the well known American BMD enthusiast and BMD health researcher Pat Long it is worth noting that in the three categories she uses the term “At Risk” for the ‘worst’ grading. This category is often quoted as “affected” which is not quite the same thing. There may be other factors which cause the DM symptoms to develop and affect a dog and we do not know them all yet. Fortunately a low percentage of Bernese actually become symptomatic. An “at risk” DNA test result would definitely indicate a much higher risk of developing the disease as an issue but it is not a certainty as the figures in Pat’s data explain. In some ways this may not be a simple “Yes/No” recessive gene situation. Whilst some believe all ‘At Risk’ dogs would become affected if they lived long enough there is also another school of thought that there may yet be another gene involved in DM actually occurring or not. Whilst research continues we have to work with SOD1A and SOD1B and accept the fact that whilst not all ‘At Risk’ dogs develop symptoms they are much more likely to.

SOD1A and SOD1B Clarification

To avoid any confusion the relationship between these two mutations and their causative effect should be made clear. A carrier of SOD1A who is clear of SOD1B mated to a clear of SOD1A and a carrier of SOD1B is a CARRIER TO CARRIER mating. As Pat Long puts it “They are two different mutations in the same gene, at different loci on that gene. Each mutation originally occurred on a normal copy of that gene, which is why we don’t see both mutations present on the same gene.

Realistically, it doesn’t matter which mutation is present, if there is one mutated gene then the dog is a carrier. If both genes have mutations then the dog is at-risk. If you breed an SOD1-A carrier to an SOD1-B carrier, it is a carrier to carrier breeding and each puppy has a 25% chance of being clear, a 50% chance of being a carrier, and a 25% chance of being at-risk”

What is the Situation in Britain?

In early 2015, despite some claims on social media, the situation in the UK BMD population was not clear with nothing other than anecdotal information to substantiate anyone’s opinion. Some claimed we had no DM issue to bother with other felt it was widespread. To help to clarify matters a little, as well as boost general awareness, the GB club decided to use some funding from it’s health fund to supply DM testing to a sample of members at certain club events in 2015. Individual results would only go to the owners but summary results would be sent to the club from the testing laboratory. In this way we planned to obtain a basic datum position of where the UK BMD population stood. We accepted it would only be a relatively small sample but we felt we needed to make a start. In the future we would be able to carry out a similar survey to assess progress, or otherwise.

In mid 2016 we were able to announce the results which are as follows.

DM (SOD1A)

Clear 30 out 61 = 49.18% Carrier 26 out 61 = 42.62% At Risk 5 out 61 = 8.20%

DM (SOD1B)

Clear 55 out of 59 = 93.22% Carrier 4 out of 59 = 6.78% At Risk 0 out 59 = 0%

Accepting any statistical limitations of the numbers involved, these figures would appear to be in line with other populations that we know about so in one sense we can say that UK Bernese do not have a particular problem with DM but in another sense we have the same problem as everyone else. This is not surprising as not only do our Bernese originate from the same sources as everyone else’s but appears clear that the original DM (SOD1A) mutation occurred a long, long way back before many of our modern breeds became independent breeds.

Adding together the SOD1A and SDO1B results it shows that about 50% of the breed should be considered as ‘carriers’. Add in the 8% of ‘At risk’ and you are looking at close on 60% of dogs that are implicated in one way or the other or to put it another way about 40% that aren’t.

Ideal World v Bigger Picture

In an ideal world we would be able to say only breed with clear dogs and bitches but of course we have to operate in the real world. Reality says that there are many other considerations for the breed and most would say that many of these are more important for the breed than DM. We should not ignore factors like hips, elbows and temperament, to do so would be to completely forget good work that has been done over many years, and continues to be done, in these areas. We should not take things for granted or we will only regress in these areas. A bigger issue for many than DM is cancer and there is now a test for our breed’s biggest issue, see elsewhere on this site for more information, and there is certainly a strong case to be considered that this is much more impactful and serious condition for OUR breed than DM.

Undermining all these issues is the big issue facing many breeds today as advised by many Kennel Clubs across the world and many veterinary institutions, namely genetic diversity within breeds. This is the single biggest problem we all have to address and it would be ridiculous to rule out 60% of our gene pool to deal with a single problem that, clinically speaking, can be avoided with a much less severe application of the test results. Lack of general genetic diversity has a negative impact on most of our existing issues. For several years now the Kennel Club has had a section on it’s web site where the Coefficient of Inbreeding, CoI, for any particular combination of dog and bitch can be calculated for you. As mentioned elsewhere on this web site the club recommends that breeders use this and it should be considered a serious health improving tool not dismissed as a gimmick.

Summary

As in many walks of life nowadays, the situation regarding DNA testing is a rapidly changing one. Not much more than couple of years or so ago in our breed we were not concerned with any DM test but now we have two to utilise. So, we must be careful not to judge yesterday’s actions with the background of today. In relatively recent times DM testing was not a feasible option for breeders so older dogs around today may well not be from tested parents but if they are to be used for breeding there is nothing stopping them being tested today.

As with all other diseases DNA testing for DM should not be used as “witch hunt data” to persecute people or dogs but should be maturely and sensibly considered by breeders to improve the breed in the long term. Dogs tested as “at risk” can, and most probably will, still have healthy lives. DM should not be become an obsession or absolute priority but neither should it be totally ignored. Like most things in life and breeding there has to be sensible middle ground and we have to find it, both as individual breeders and as a collective breed community.

In some overseas communities, breeders openly publicise the DM status of their dogs, many can be found recorded on Bernergarde and other sources.

We are extremely grateful to Pat Long for contributing her (as usual) excellent explanatory article. This article is are available below and was first printed in the December 2014 club magazine.

With the ongoing development of our breed we are where we are but we have to try and improve as we go forward. If we totally ignore all the information then it is inevitable that some of the ‘At Risk’ cases will be bred together and it would be logical to expect that incidences of DM will appear at younger ages and in more dogs as the generations pass. Remember currently, this disease does not typically become apparent until past general breeding age, especially for bitches, so it is of no value assessing the dog itself, DNA, or maybe family history, have to be the guides. Dogs of ‘At Risk’ status can have a full breeding career, maybe hundreds of puppies for a stud dog before developing any symptoms. What contribution would that make to the future of our breed?

Recommendations

In view of all the above information and looking at the situation in other countries the Bernese Mountain Dog Club of Great Britain strongly recommends that all breeding combinations have at least one completely clear (SOD1A AND SOD1B) parent involved.

With this policy the disease will not be created and there will not be another Bernese and their family suffering the trauma and distress of this condition. There is no reason to take any chances with this and no excuses for not minimising the risks not only for your puppy buyers but for the future of the breed. The club feels this is a common sense solution and note that many clubs across the world have come to the same conclusion.

Sometimes testing will not be needed as the status of puppies will be clear from their parents, this is just as valid as an individual test. The bottom line is that all breeders should know the DM status of all their breeding dogs. The tests cost a tiny fraction of the price of a puppy and there is no reason nowadays to not be able to look your puppy buyers in the eye and say their Bernese should not be developing DM.

Knowing your dog is ‘At Risk’ is better than not knowing his or her status at all so the club commends those who test over those who don’t. If you have an At Risk or even a Carrier dog with other qualities that you wish to breed from then ENSURE you only mate to a CLEAR graded dog. It is only common sense and responsible breeding on all levels.

Breeders may even wish to consider testing all puppies in a litter prior to selecting puppies to keep or move on. This could especially be the case if the litter is to produce a puppy to be used for breeding, especially if to put to a particular dog that is known not to be Clear.

Advice

So please read the articles and absorb the information and, if you are a breeder, just try to incorporate the DM factor into breeding decisions and do the best things for our breed’s future. There are many things to consider and breeding choices are always a compromise between multiple issues as there are no genetically perfect dogs, just make this condition one of the many issues considered in breeding decisions and do not produce ‘At Risk’ puppies. Just because DM is easy to test for does not mean it is the most important thing we have to deal with but it is significant and improvements for our breed can easily and reasonably be made.

If you are a prospective puppy purchaser then ask breeders about the DM status of the parents and other antecedants and relatives. The breeder may have taken a considered decision and not have the option of using a clear bitch but in that case should have used a clear stud dog. There is no longer any excuse for ‘not knowing’ the status of your breeding dogs, the cost of a test is a fraction of the sale price of a puppy. It is true that, despite the attention given in some places, DM only actually affects a small percentage of our breed but if you are in that percentage it is 100% affecting your dog and your family’s life. Producing an affected dog should be viewed as an avoidable situation and does not need to happen in the future.

Steve Green
BMD Health Co-Ordinator

FOOTNOTE: The club’s funding of testing was a one off venture to establish a picture of the situation in Britain. Whilst some took advantage of it for breeding stock it was never intended as a long term assistance for breeders, the club does not have resources for this and has other areas to address. The cost of testing is paltry compared to the price of a puppy and responsible breeders should be prepared to fund this themselves.

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