Part of the official UK Kennel Club testing scheme in Leonberger
Laryngeal paralysis and Polyneuropathy (LPPN) in an inherited neuropathy in dogs. Laryngeal paralysis (LP) results in loss of function of the larynx leads to breathing difficulties, reduced exercise and heat tolerance, and increased risk aspiration pneumonia. In addition, atrophy of laryngeal muscles and the decreased movement of the attendant laryngeal cartilages result in the airway remaining open during swallowing of food and water. Laryngeal paralysis is often reported as part of a more generalized length-dependent polyneuropathy (PN), which manifests with additional signs that include proprioceptive and motor abnormalities, slowly progressing pelvic limb weakness, and loss of limb muscle mass.
The disease is heterogenous, meaning the genetic variants that cause the disease vary between and within breeds. A form of LPPN in Leonberger, Labrador Retriever and Saint Bernard dogs has been associated with the CNTNAP1 gene (LPPN3). The average age of onset of this form for the disease is 3.4 years in Leonbergers, 2.1 years in Saint Bernards and 7.5 years in Labrador Retrievers. Polyneuropathy is widespread in Leonbergers, and to date two additional variants, LPN1 and LPN2, have been identified.
The single nucleotide substitution in the gene called CNTNAP1 that causes Laryngeal Paralysis and Polyneuropathy in Leonberger is autosomal recessive. This means that dogs that carry two copies of the mutation (homozygotes) will almost certainly develop Laryngeal Paralysis and Polyneuropathy during their lives. Dogs that carry a single copy of the mutation (also known as carriers or heterozygotes) will not develop Laryngeal Paralysis and Polyneuropathy as a result of the CNTNAP1 mutation, but they will pass the mutation onto about half of any offspring they have. Breeding dogs that will not develop Laryngeal Paralysis and Polyneuropathy should be the breeder’s priority, with a reduction in mutation frequency within the whole breed being the secondary, longer-term target.
Carriers can be bred from safely, provided they are mated to a dog that has also been tested and is clear of the CNTNAP1 mutation (i.e. carry no copies of the mutation). If a carrier is mated to a clear dog approximately half of the resulting puppies will also be carriers, so should be tested themselves prior to breeding. Breeding carriers to tested, clear dogs is safe, in terms of avoiding dogs affected with Laryngeal Paralysis and Polyneuropathy, and will help to maintain the genetic diversity of a breed. It is therefore encouraged, particularly in the first few generations following the availability of a new genetic test, so that other desirable characteristics and traits can be preserved before the frequency of the disease mutation within the breed is gradually reduced.