Another issue that continuously demands attention is the question of just what diseases are in fact genetic, and who do we determine to be credible on the subject. All involved will surely continue to grapple with this issue as not even the geneticists themselves are in agreement.
Debbie Martin: We’re having problems defining who the experts are. For example, a local vet will say "no, that’s not a genetic disease" but they won’t hear from the head of neurology of orthopedics or orthopedics at Davis that it is genetic. How should we choose the people that we’re going to believe regarding what is or isn’t genetic?
Dr. Padgett: There’s a little bit of difficulty in that obviously, because some people define themselves as experts, when in fact they are not experts. Most clinical, regular veterinarians don’t know beans about genetics. I mean, most schools do not teach genetics. They give it in pre-vet so they have some genetics in their training but they don’t really understand genetics. I would accept the head of neurology at Davis as an expert unless I had good evidence otherwise because he’s in a position where he gets a lot of cases that influence his decision.
Debbie Martin: Say we have a disease show up, should we record it, and start tracking it and looking for it?
Dr. Padgett: I would record it and track it but not necessarily call it genetic. And, I wouldn’t necessarily discriminate against it until reasonable evidence said it was genetic. Reasonable evidence as far as I’m concerned is:
Debbie Martin: So if a given disease is proven to be genetic in people, but there’s nothing in the canine literature that says that it’s genetic, can we still make the assumption that it is genetic?
Dr. Padgett: I would work on the assumption that if it’s genetic in one species, it’s likely to be genetic in another species. And that’s a criteria, again, that I use.
Genetic vs. Environment
A continuous source of healthy discussion is whether
diseases that could be caused by the environment should be tracked as
genetic in our bloodlines. Environmentally induced diseases, which
could also be genetic, can throw confusion into the efforts of a
breeder trying to identify genetic defects in a line. This greatly
emphasizes the importance of getting a good diagnosis.
Debbie Martin: What do you think the role of the environment plays in the development of cancer?
Dr. Padgett: I think a huge role. But I can’t tell you what it is for each specific cancer in dogs. I can’t think of one that we really can tie to a specific environmental cause. But I think it is like in people, it’s environmental. When we look at overall cancer in dogs it’s about like overall cancer in people, about the same frequency. So I think whatever affects people affects dogs too.
They’ve done a fair amount of cancer research on the distribution of cancer in dogs. There are some good size studies because they thought that dogs might be sentinels for cancer in people. The areas where cancer is high in people in the country, cancer is also high in dogs - in the same areas. There have been two huge California studies based on half a million dogs following cancer in the households with dogs.
Debbie Martin: Now, what about breeding them together? Say you have a family of dogs that has a lot of cancer, but some of the cancers are less harmful than others. Does that make a dog safer to breed?
Dr. Padgett: It depends on whether or not the cancer’s genetic in the first place. Breeding may not influence it at all, in many cancers. Probably in most cancers breeding is not an influence because it can’t affect anything that’s not genetic. You have that same question in those not related to cancers specifically. It’s a difficult question to answer because we don’t know for sure the role of the environment.
All genetic diseases are affected by the environment; some of them much more strikingly than others. For example, I can alter my own phenotype, which is diabetic phenotype-I’m diabetic. I alter that with insulin. But using insulin extended my own life span 15 years or 10 years anyway. And, if I quit using insulin I’d be dead in probably three weeks, or three months anyway. I’d be a goner. All genetic diseases are influenced by the environment.
You can influence Hip Dysplasia by the environment. We talk about that all the time. Some people really confuse that and think that environment is more important than genetics, and it’s not. You never get Hip Dysplasia if you don’t have the genetic disease associated with the genes associated with Hip Dysplasia. Once a dog has Hip Dysplasia we can make it better than it was by how we handle that dog. We can improve the phenotype but we can’t change the genetics of the dog. And, we will not make a dog dysplastic no matter what we do with diet if he’s doesn’t have the genes for Hip Dysplasia because it is a genetic disease. But if a dog has the genetics for grade one dysplasia, for example, we can probably turn that into a grade two by making it eat more or by how we hold the legs. We can create a mimic of the disease.
So you can cause a phenocopy, but if the dog is treated normally, no matter what we do to that dog, he will not develop genetic Hip Dysplasia, and he will not transmit the disease to his offspring.