Leonberger dogs may suffer from neuromuscular disease collectively termed Laryngeal Paralysis - Polyneuropathy (LPPN). Many LPPN affected dogs suffers from laryngeal paralysis; clinical signs include noisy breathing, a change in their bark, or even difficulty breathing due to involvement of the larynx and laryngeal folds in the throat. Additionally, dogs may show signs of slowly worsening exercise intolerance and 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. Eventually the disease may progress to the point where surgical intervention for laryngeal paralysis is required or 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. 

Dogs with LPPN may show only signs of laryngeal paralysis or only gait abnormalities at the onset of disease.

Research carried out at the University of Minnesota, the University of Bern, and the University of California, San Diego - Comparative Neuromuscular Laboratory indicates that polyneuropathy / laryngeal paralysis within the Leonberger breed is a group of several genetically distinct, but clinically similar diseases. We have mapped three major genetic risk loci and identified the causative mutations that we now term LPN1, LPN2, and LPPN3.

• We have also identified LPPN3-D/D affected mixed breed dogs, and the mutation is present in several breeds.