Part of the official UK Kennel Club testing scheme in Leonberger
Polyneuropathy Type 1 (LPN1) in Leonbergers and Saint Bernard dogs is an inherited polyneuropathy (PN), which is characterised by generalised weakness, low muscle tone, exercise intolerance, gait abnormalities and muscle atrophy of the pelvic limbs. Degeneration of the recurrent laryngeal nerve results in laryngeal paralysis, which causes abnormal barking and breathing sounds. Age of onset ranges from less than one to 11 years of age. LPN1 accounts for approximately 11% of all PN cases in the Leonberger breed, and 2 additional variants have been identified as well, LPN2 and LPPN3.
The 10bp deletion in the gene called ARHGEF10 that causes Polyneuropathy in Leonberger is autosomal recessive. This means that dogs that carry two copies of the mutation (homozygotes) will almost certainly develop Polyneuropathy during their lives. Dogs that carry a single copy of the mutation (also known as carriers or heterozygotes) will not develop Polyneuropathy as a result of the ARHGEF10 mutation, but they will pass the mutation onto about half of any offspring they have. Breeding dogs that will not develop 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 ARHGEF10 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 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.