At the beginning of this year the VHNK offered a risk assessment for polymyositis. This was meant as a temporary solution until Fit2Breed becomes available. Unfortunately, it turned out that the way Prof. Leegwater assesses the risk does not meet the expectations of our breeders at home and abroad.
Breeders get a result for one coincidentally chosen breeding pair, even if several of the given breeding pairs are assessed as low risk. It is done so as not to allow any conclusions about carriers.
As a scientist, it is important to Prof. Leegwater that the assessment does not make it possible to conclude whether dogs are carrier or free of polymyositis. If that were possible, dogs would be unnecessarily excluded from breeding.
Why are no results released from Utrecht for the other dogs? The answer lies in the following writing that we published on the website in December:
Polymyositis research (Dr. Peter Leegwater, Drs. Yvet Opmeer & Dr. Paul Mandigers)
There is some good news. We have found the mutation that can be associated with polymyositis. All the dogs with polymyositis which are examined by use have the mutation. This mutation is can be found close to two important genes involved in the functioning of the immune system. It also turns out that Kooikerhondjes suffering from polymyositis have an abnormal function of these two genes. So the mutation has no doubt a meaning.
However, not all the Kooikerhondjes with this mutation become ill. Kooikerhondjes that are homozygous for this mutation (they therefore have the two different alleles) have an increased risk, but not all of them will get sick. We see this more often with immune-mediated diseases. Environmental factors or variations in the rest of the DNA can cause a dog to become ill or not. That is why we call this mutation a risk factor. Also heterozygous Kooikerhondjes (Kooikerhondjes with only one deviating allele) are also at risk. That risk is very small (probably less than 1 percent) but present. Because there are many Kooikerhondjes with this mutation, we see that about 1 in 3 leaders of polymyositis is heterozygous (carrier) for the hereditary risk factor.
Pedigree research showed that other factors must play a role. We noticed for example that in some litters several dogs got sick, which would not make sense if the mutation is only expressed in a small proportion of the Kooikerhondjes. However, if there is a variation in the DNA that makes a dog more at risk or less at risk, this explains what we see in some litters.
In order to investigate this factor the DNA of a group of heterozygous leaders was compared to a group of homozygous leaders which have remained healthy throughout their lives. This comparison led to signals on two chromosomes that have been further investigated.
The first signal led to a DNA variant that seemed promising, but it turned out that it had a high frequency in the entire population. It was a false positive result that was a coincidental. The second signal could not yet be traced back to a variant in a gene. This investigation will be continued.
We hope that this resolves any uncertainties regarding the received results.
If you still want to request a risk assessment, you can do so via: Application polymyositis risk assessment.