It has been some time since I added a post to my canine health screening series. I thought I would continue the series with a general post about DNA testing which is one tool breeders can use to help screen for certain diseases.
DNA testing is relatively new. Within the last 10 years, researchers finished mapping the canine genome which was published by researchers from the Board Institute of MIT and Harvard in 2005. Once mapping was complete, the researchers were able to discover some of the genes that caused certain genetic diseases. Some but not all. That point is important to remember.
Eventually researchers were able to develop tests to identify some of these “bad” genes. The tests are specific to each breed based on that breed’s DNA make-up and whether the specific disease is present in that breed. These diseases may also be present in mixed breed dogs, but with pure bred dogs they have a better idea of their DNA make up so it is easier to develop the test. This series is about what puppy buyers should consider when buying a purebred dog so my focus is on the pure bred dog.
In order to understand DNA testing you have to have a basic understanding of genetic inheritance. There are different modes of genetic inheritance, but for the purposes of this series, I will only be dealing with single-gene simple recessive and polygenic inheritance.
Very simply, with single-gene simple recessive diseases, the puppy must inherit two mutated genes (one from each parent) in order to inherit the genetic disease. These genes are recessive so a puppy having just one of the “bad” genes will never express the disease. DNA tests work very well to identify which dogs carry certain recessive genes and therefore, a breeder can avoid pairings which will produce affected puppies. A couple of examples of diseases that are the product of single-gene simple recessive inheritance in dogs are PRA (Progressive Renal Atrophy) and EIC (Exercise Induced Collapse).
Polygenic inheritance is more complex. Polygenic inheritance involves many genes and factors (possibly environmental), that may cause a particular disease in a particular dog. Polygenic inheritance is more difficult to predict through DNA testing because as far as I know, the researchers are only to the point where they can identify a single gene that is present in dogs who have expressed a disease. The presence of that one gene alone cannot predict whether a dog will, or will not, develop the disease.
A couple of examples of a canine disease/conditions which are the result of polygenic inheritance are hip dysplasia and DM (Degenerative Myelopathy). Predicting hip dysplasia is not done through DNA testing but through phenotype identification or using an x-ray to examine the sire and dam to see if they are themselves dysplastic. DM, on the other hand, is predicted by a DNA test and by looking at parents and grandparents to see if they have expressed the disease. There is no definitive test to predict polygenic diseases with 100% accuracy at this time.
The next post in this series will be about some of the pitfalls of DNA testing.
That is a very interesting topic and we look forward to reading about the pitfalls. Have a terrific Tuesday.
Best wishes Molly
Thanks Molly. You too!
Can’t wait for the rest of the series. I am confused now I thought DM was a single gene like EIC as they both are noted as normals, carriers and affected and you need two of the same to make the gene. Gene stuff is way to complicated for me and to think I went to animal school. lol
Maybe the reason you thought that was because it has been sold by some breeders as a single recessive, but it is not. It is polygenic.
Interesting stuff.
Dug your comment out of spam. Silly spam filter!
I found several of yours in there too since you switched to self hosted. I have no clue how that all works.
I’m excited about this series as I am always wanting to learn more about genetics and what breed of dogs are prone to certain diseases.
I’m not sure I knew Thunder was a DM carrier. I have to think on this now, a dog is “at risk” “not at risk” or a “carrier” with DM? I think that’s right. That means that Thunder carries the gene but will not get DM? God I flunked this stuff in high school!!
With DM the results can be Normal, Carrier, At Risk/Affected. Those are the terms you are likely to see used with this disease. In my next post I will go into a this, but there have been carrier dogs to come down with the disease. Only a few, but it has happened. It is a complex disease. There is ongoing research but it is thought that there may be another form of the disease that the current test does not screen for or it could be the test is flawed. It is not uncommon that a better version of a test is substituted for an early one. DNA testing is just in its infancy.
Genetics are so fascinating! I am glad that breeders are using them as a tool to lessen the chances of certain diseases.
Looking forward to the rest of this series, it’s a great topic. It’s something I know very little about, so all of this is new to me. It’s nice to know that with the advances in screenings available breeders will have the ability to make wise decisions when it comes to breeding.
Science was my worst subject in school, but DNA and related subjects are one part of it I found much more interesting. I’m looking forward to learning more.
Good information, thanks for posting!
Love that you’re continuing with the health screening series. Definitely a topic I’m clueless about and interested to know more! 😀 I don’t know if Donna is at risk of anything since she is born to strays, but I hope she comes from a healthy family 😀 At least she doesn’t come from a pet shop, most of the pet shop/local breeder animals I know seem to have a high chance of doing badly from a young age healthwise – – … but maybe I’m just generalising…lol
When looking at puppies, do we ask the breeder for results of the hip tests or is this something that’s automatically given? Thanks.
It is not automatically given. Sometimes the breeder will give you a number. If it is an OFA number you can double check it on their site. They also may provide a copy of the certificate which will have the information and sore for that dog. If they do not supply either of those two things, you should ask.
There is also something called Penn Hip. I don’t think they have an open database so you should ask for the score and maybe a certificate.
Either OFA or Penn Hip are acceptable for hips.
So that you can see what and OFA page looks like, I am linking to Freighter’s page. You will notice he has had a lot of tests done. Not all of those tests are something every breed would test for and some breeders may choose not to test for some. But on that list is his hip score.
Freighter’s OFA Page