Within the last years, a few kennels throughout Europe reported on the sporadic birth of puppies, who suddenly developed abnormal gait and progressive muscle atrophy from an age of around 3 months on. First, breeders and owners assumed that they had to deal with singular cases, but soon it turned out to be a common new problem, a new Greyhound disease, not yet described in scientific literature.
Clinical Symptoms
Usually, first signs of the disease occur at an age of 3-4 months. Affected puppies quite suddenly show an abnormal gait with arched back and rear weakness, which may suppose an injury in loin. Within a few days or weeks, condition gets worse, the puppies visibly loose muscle and hardly can walk or run for more than 200-300 meters. Even just a few steps lead to fatigue, puppies are no more able to fully stretch the knee joints. They show a strange, "bunny-like" hopping gallop with turned-out knees, later on they collapse and cannot walk anymore. After a few minutes of recreation, they recover strength and can continue walking for another short distance.
In addition to the abnormal gait, neurologic deficits come to the fore of the pathogenesis. The spinal reflexes are highly decelerated resp. totally absent, especially the patellar tendon reflex. In contrast, sensoric and proprioreceptive functions are usually not affected.
With increasing age, muscle weakness is more and more progressive, the gait gets wobbling and unstable, up to the dogs cannot get up and walk without help any more. It differs from case to case which muscle groups are particularly affected. Usually shoulder and thigh, as well as temporal, back and in some animals also the laryngeal muscles are highly atrophic. The latter are standing out because they cannot bark and are sometimes dyspnoeic. Affected puppies don't show any sign of pain or disturbed well-being, they are alert and full of joie de vivre until the end. However, they only reach an age of 9 to 13 months until they have to be put to sleep because of their progressive muscle atrophy.
Differing from the symptoms described above, there are known cases with far earlier and heavier progress, which had to be euthanized in far younger age (6 to 8 weeks).
Autopsy Findings and Pathogenesis
Usually, autopsy doesn't show any notable macroscopic findings except of a severe general muscle atrophy. In all Neuropathy puppies who underwent autopsy a mild hydrocephalus internus could be found, but this doesn't explain the clinical symptoms in total. Only with special stainings of nerve sections the underlying defects can be detected. Affected puppies show a nearly complete degeneration of peripheral nerve axons, thus leading to an omitted neuronal stimulation of the muscle, resulting in muscle atrophy.
The supposed cause for the axon degeneration is a defect of certain transport proteins, who are responsible for the nutrition of the axon from its beginning at the nerve cell body to the end. If a genetic mutation leads to the expression of a dysfunctional protein, the axon cannot be supplied with enough nutrients and will decay.
Looking at the pedigrees of all affected puppies and their relatives gives a strong hint that we could have to do with a monogenic autosomal-recessive trait. So called "carriers" (who have one healthy and one mutated allele), are phenotypically healthy, powerful dogs - but if two of these carriers are mated and a puppy inherits a mutated allele from both, it will be affected by the disease.
Neuropathy Project
Until now, Greyhound Hereditary Neuropathy isn't described in veterinary medical literature yet, there is still a a great demand for further research. Thanks to the help from a lot of responsible breeders and owners, we could collect a large amount of samples from affected puppies and their parents, grandparents, littermates, half-siblings and other relatives. Using these samples the disease could be further characterized - and they shall also be used to develop a gene test in the future. Unfortunately, until now the number of samples from affected puppies we have is still to low to identify the defect gene definitely. We need as much genetic material from greyhounds as possible - from affected puppies, their parents and relatives, but also from greyhounds out of neuropathy-free bloodlines. They could give true negative controls, who are also very important to characterize the gene. It's just a few milliliters of blood what we need as a sample. Until now, we could collect DNA from 5 affected puppies - if we would get 5 additional ones, the chances for the development of a gene test are very, very high!
PD Dr. Cord Drögemüller at the Institute of Genetics of the University of Bern/CH is heading several research projects about genetic diseases in dogs. He kindly agreed to include the disease Greyhound Hereditary Neuropathy in his research. More information about the Neuropathy Project you also can find on the institute's webpage .
Searching for the first common ancestor, who is doubled up in the pedigrees of all affected puppies on maternal and paternal side, we had to go back to the 1970ies. At the moment we have to assume that nearly every greyhound who has scandinavian ancestors from that time could be a carrier. Some of the famous stud dogs of the last 20 years must have carried the defect and bequeath it to a part of their offspring. Outcross matings can prevent affected puppies in a litter, but the recessive defect will not disappear - the next generation will carry the risk as well. The only way to get control is to have a possibility to find out if an animal is a carrier of the defect gene or not.
August 2009 ~Breaking news from the Greyhound Hereditary Neuropathy Project! The gene mutation has been found and a gene test for identification of the asymptomous carriers is available.
Please contact the Vetsuisse Faculty of the University of Berne, Switzerland:
http://www.genetics.unibe.ch/content/e2353/e2982/index_eng.html - a form for sending in the samples will be ready within the next days.
Analysis of the first samples already showed that the defect is alarmingly widespread in the Show Greyhound population - we urgently recommend testing of each breeding animal to make sure that two carriers are never mated.
Detailed information will follow soon - for the moment I want to inform all interested breeders in advance.
Best regards, Dr. Barbara Kessler
Article credit Dr Barbara Kessler of Rumford Greyhounds http://www.houndstation.de/
