Immune-Mediated Polyarthritis

So we have a possible culprit for the mystery Shikoku limp. Up until now panosteitis has been the suspect, and in at least 1 case a diagnosis was made based on x-rays. However, some things about the Shikoku mystery leg pain do not add up to pano. Panosteitis is supposedly self resolving in that dogs grow out of it at around 18 months. However, the symptoms in Shikoku are often lifelong.

I have been working to try and track the issue in the breed, since it seems to almost certainly be hereditary, and my veterinarians have been supportive in trying to help diagnose the issue. And (drumroll please) we have a new prime suspect: Immune-Mediated Polyarthritis aka IMPA.

Immune-mediated (aka autoimmune) conditions occur when the immune system is overactive and attacks the body in various ways. Hyperactive may be a more appropriate term because one part of the immune system is revved up and working in overdrive.  Immune-mediated disorders have an underlying genetic predisposition, like they do in humans; this genotype association in affected dogs has recently been located on the DLA-79 allele (Dog Leukocyte Antigen) of the major histocompatibility complex (MHC) system. Other factors predisposing to overactive immune system responses include environmental factors like vaccines, drugs, food, chemicals or drugs as well as stress situations that act as “triggers” of this immune response.
Polyarthritis is an inflammation of multiple joints.
In the case of IMPA, white blood cells (aka neutrophils) invade the joints of the body. They are not supposed to be there. They are supposed to be fighting bacteria and pathogens in the surrounding tissues. This causes swelling of the joints, pain, and difficulty walking or standing. Other symptoms may crop up, too, such as weight loss, anorexia, fever, fatigue and can affect the lymph nodes draining the inflamed areas.



The fact that it is an immune system related issue comes as no shock to me. We know the Japanese breeds are very inbred off a very small number of breed founders. Since there are a number of other immune related issues seen in the Japanese breeds such as VKH in the Akita, severe allergy/skin issues in the Kishu etc, a diagnosis of IMPA in the Shikoku makes a lot of sense. It has also already been found in the Akita. The one promising line in the above text I pasted is this genotype association in affected dogs has recently been located on the DLA-79 allele (Dog Leukocyte Antigen) of the major histocompatibility complex (MHC) system


Is it possible that we could find out if the marker for this issue in the Shikoku can be found and tested for? C'mon my genetic geek friends, show me your skills :)

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