The Greyhound Show

23.9.2012

Neuropathy FAQ

Filed under: Gesundheit — BKM @ 19:07

Da es anscheinend immer noch Unklarheiten über diese eigentlich inzwischen allseits bekannte Krankheit gibt, noch mal eine Zusammenfassung – verbunden mit dem dringenden Appell an zukünftige Welpeninteressenten, ausschließlich Welpen aus getesteten Elterntieren zu kaufen!
Vorerst nur auf Englisch, bei Nachfrage wird die deutsche Übersetzung gerne nachgeliefert.

How is the disease transmitted?
Greyhound Neuropathy is a recessive hereditary disease, which only can occur if both parents are carriers and a puppy got one defect allele from each of the parents. Matings between one carrier (heterozygous for the mutation) and one clear (homozygous free) parent will produce a litter of carriers and clear puppies, but never a neuropathy puppy. In contrary to diseases caused by infectious agents (viruses, bacteria or parasites) a vertical transmission from one animal to another is impossible – a clear dog can never turn into a carrier.

Are carriers less healthy than clear puppies?
One intact copy of the NDRG-1 gene is sufficient to maintain the function of the gene, therefore carriers will never develop symptoms of neuropathy. They are as healthy as their clear littermates and do have the same life exspectancy (assumed that they don’t suffer from any other disease of course – here we talk only about Neuropathy).

Isn’t the risk higher for a carrier that he develops another mutation of his intact NDRG-1 allele and therefore could get sick?
It’s extremely unlikely that a new mutation could affect the same gene. Even if mutations are a biologic principle, occuring on a regular base in cell divisions, the chance is close to zero, that exactly the same genetic region out of the approxinately 20.000 genes in the dog’s genome is affected by a new mutation.

But why is stated in the lab test result of a heterozygous carrier then, that he has “an extremely low risk to develop the disease”?
This statement is not based on medical-genetic facts, but on judicial consideration. The lab doesn’t want to be liable for any cases of the disease, no matter how unlikely they might be. From a medical point of view, it is absolutely impossible that a dog who is heterozygous for the mutation (a carrier) will develop this disease later on.

Why should carriers still be used for breeding?
On a first view, it sounds more than reasonable to get rid of the mutation as soon as possible. Neuropathy is a fatal disease with a life exspectancy of mostly less than one year for affected puppies.
But we shouldn’t forget that the gene pool of show bred Greyhounds is already quite limited – a further reduction would probably create new problems. We also shouldn’t forget that even carriers could also have some other, very valuable genes, which shouldn’t get lost from the gene pool. Considering the whole population, it is the better method to breed out the mutation step-by-step. As long as carriers are only bred to clear dogs, no neuropathy puppies will be born. That’s the most important for the moment! If clear puppies from such combinations are preferrentially chosen for continuing the bloodline, the mutation will be lost in a few generations – but without reducing the gene pool!
Neuropathy is a terrible disease, but it’s the only one we can control so far. I’m worried far more by all the other problems which are popping up here and there: several autoimmune diseases, heart diseases, liver shunt, bloat… luckily they are not very frequent yet, but they are impossible to predict for a future litter.

Which Greyhounds should be tested?
Any Greyhound who has Show Greyhounds in his pedigree should be tested before breeding, no matter how far they are behind, and no matter if he has a “pure” show pedigree or is a mix between show and racing lines. The mutation must have occurred somewhere in the 1970ies or even earlier, and it is extremely widespread within the population. Carriers still appear even from bloodlines which were considered as unsuspicious before, and we had to learn that the defect is far more prevalent than we ever suspected.
An exemption are offspring of two clear parents: they cannot have inherited the mutation, therefore they haven’t to be tested again. A frequent objection to that is that a new mutation could have occurred meanwhile – the answer is no, it’s extremely unlikely that the same gene could have mutated again – and even if, it would definitely not be the same deletion which can be detected by the gene test. The likelihood that a new mutation could happen is as low as of the mutation of any other gene.

How can we prevent that new genetic diseases appear and will spread over the population again?
We cannot prevent the occurrence of new mutations, but we can take care as much as possible, that they are not spread over the population as fast again. As Show Greyhounds are a numerically quite small breed, every breeder is bearing a big responsibility for the whole population. If we continue using a few top stud dogs only, we will produce another genetic bottleneck where some more parts of the gene pool get lost and some few alleles are enriched. We must be well aware, that EVERY organism is burdened with a certain amount of defective genes! As long as they are heterozygous, they might not have any detrimental effect (in most cases), but if they are doubled up one day, they might cause another, severe disease. Increased homozygosity in a more and more inbred population increases the risk of doubling up unwanted genes considerably.
Breeders should not only concentrate on the actual topwinning lines only – for the moment it is far more important not to loose another bloodlines, just because they’re not winning so much in the show rings today. But they can be very important in the future, to maintain as much heterozygosity in the gene pool as possible. Another appeal goes to the owners of stud dogs: even if it’s always a great pleasure for his owner when a stud has a lot of inquiries, the consequences for the whole breed should not be forgotten. In big populations, 20 mating or more are not a problem, but for small breeds like our Show Greyhounds, even 5 litters per stud are rather too many!

Dr. Barbara Keßler
Institute for Molecular Animal Breeding and Biotechnology
Ludwig-Maximilians-University Munich

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