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We recommend that dog breeders take into consideration the DM test results as they
plan their breeding programs; however, they should not over-emphasize this test result.
Instead, the test result is one factor among many in a balanced breeding program.

~DM Research Team, 2008

This is a quick and brief synopsis of the breeding expectations for various combinations of Degenerative Myelopathy DNA test results. In time this page will be cleaned up, and updated with more information on DM.

The researchers at the University of Missouri and the Broad Institute have discovered a gene which is a major risk factor for Degenerative Myelopathy. There are two possible forms (or alleles) of the gene, the normal form (N) and the mutated, or abnormal, form (n). (Note that the researchers call these "N" for "Normal" and "A" for "Affected" or "At Risk", but we have chosen to follow traditional genetic conventions here.) Every Boxer has two alleles, inheriting one from each parent; the combinations can be two copies of the Normal gene (homozygous normal), two copies of the mutated gene (homozygous mutated), or one copy of each gene (heterozygous).

clear gene at risk gene
Normal (Clear) Gene
N
Mutated (At Risk) Gene
n

The number of each gene a Boxer gets determines its DM risk. The normal gene is dominant, which means that any time a dog has even one normal gene, it is very unlikely to ever develop DM. A dog with two copies of the mutated gene is more likely to develop DM; however this is not a foregone conclusion and there are other factors involved in the expression of the condition.

clear dog
Homozygous Normal Dog
(Clear - NN)

This dog has two copies of the normal gene. It will not develop DM and will not produce puppies that will be at risk for DM, regardless of the DM status of the dogs to which it is bred.

at risk dog
Homozygous Mutated Dog
(At Risk - nn)

This dog has two copies of the mutated gene. It is at risk of developing DM - though not guaranteed to do so. It may produce puppies at risk for DM, if bred to a Carrier or At Risk individual.

carrier dog
Heterozygous Dog
(Carrier - Nn)

This dog has one copy of the normal gene, and one copy of the mutated gene. It is highly unlikely that this dog will ever develop DM. It may produce puppies at risk for DM, if bred to a Carrier or At Risk individual.

Below are the different genetic combinations that can occur in Boxer breedings.

An important note: While the actual distribution of genes in an individual litter may stray from the expected (i.e., a clear x carrier breeding may produce 100% clear puppies), over a large number of litters the outcome will meet the expectations.

clear x clear
Clear x Clear
(NN x NN)
100% Clear (NN)
clear x at risk
Clear x At Risk
(NN x nn)
100% Carrier (Nn)

clear x carrier
Clear x Carrier
(NN x Nn)
50% Clear (NN)
50% Carrier (Nn)
carrier x carrier
Carrier x Carrier
(Nn x Nn)
25% Clear (NN)
50% Carrier (Nn)
25% At Risk (nn)

carrier x at risk
Carrier x At Risk
(Nn x nn)
50% Carrier (Nn)
50% At Risk (nn)
at risk x at risk
At Risk x At Risk
(nn x nn)
100% At Risk

Again, at risk dogs only have a risk of developing DM, they are not guaranteed to do so. Current test results show that about 50% of the breed is at risk, with another 35% carriers - we cannot at this point afford to eliminate all non-clear dogs, or even all at risk dogs, from our breeding programs. Our goal, instead, should be to slowly work reduce the number of at risk dogs - over several generations - and at the same time increase the number of clear dogs. This is something that will likely take decades, not years, for anything like a "nearly rid of DM" status, simply because DM is so widespread, there are so many questions about what "at risk" really means, and heart issues are so much more important and should be where our focus lies for now.




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