Leonberger dogs may suffer from neuromuscular disease collectively termed Leonberger Polyneuropathy (LPN). LPN affected dogs suffers from slowly worsening exercise intolerance and may develop gait abnormalities, such as an exaggerated hitched step, especially in the hind limbs. There is often wasting of the hind limb muscles as well. Additionally, these dogs may have noisy breathing, a change in their bark, or even difficulty breathing due to involvement of the larynx and laryngeal folds in the throat. Eventually the disease may progress to the point where the dog cannot support its own weight. Biopsies of nerve from affected dogs show degradation of the nerve fibers and loss of myelin, the insulating material that normally helps speed messages along nerves. Muscle biopsies show atrophy resulting from nerve loss.
Research carried out at the University of Minnesota, the University of Bern, and the University of California San Diego, indicates that polyneuropathy within the Leonberger breed is a group of several genetically distinct, but clinically similar diseases. We have mapped two major genetic risk loci and identified the causative mutations that we now term LPN1 and LPN2. Dogs homozygous for the LPN1 mutation typically develop clinical signs of disease before they reach 3 years of age. LPN2 heterozygous and homozygous dogs may begin to show signs of disease as young as age 1, but may not show signs of disease until later in life or never at all.
The identified LPN1 mutation appears to be responsible for approximately 20% of the cases of polyneuropathy in Leonbergers, and LPN2 responsible for anther 20-25%. The other cases are apparently caused by different genetic mutations.
We have also identified LPN1 homozygous mutant Saint Bernards with a biopsy confirmed polyneuropathy and clinical signs consistent with the disease. The LPN1 test can be used in the Saint Bernard breed to aid in the diagnosis of polyneuropathy and to identify carriers in the breeding population.
The tests for LPN1 and LPN2 do not account for all confirmed or suspected cases of polyneuropathy. Until additional DNA-base test(s) are developed, the only way to confirm a suspected diagnosis of LPN in dogs that test free of the LPN1 and LPN2 mutations is via a nerve and muscle biopsy. Both symptomatic "presumed affected" as well as asymptomatic "presumed normal" dogs biopsied to confirm this status would be a tremendous help to us in these studies. At this time we are no longer accepting blood samples from presumed normal dogs for research purposes.
This work is generously supported by the Leonberger Health Foundation (USA), the Schweizerischer (Swiss) Leonberger Club, and the Deutscher Club Für Leonberger Hunde e.V. (German Leonberger Club).
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