Editor’s note: In the first of this two-part article, Dr Theresa Garton answers the following question, which was posed by one of the members of the SB-L email list:

"So what might be some of our options if the marker for any of the diseases [ARVC, DM, RD] turns out not to be a simple recessive? I understand how a recessive gene works but what if we are faced with autosomal dominant as Dr. Meurs suspects for BCM (ARVC)? Does anyone know how we would breed away from it using the marker?"

Once again, it will all depend on how common the gene is in the breed.

If it is uncommon, and it is an autosomal dominant, then you just don't breed those who have the gene, and the gene goes away.  End of problem. 

But, what if, as I suspect is possible (probable!) in Boxers, you find that you have large numbers of dogs who are at least heterozygous for the gene, and at least mildly affected?  Say, you have 25% homozygous for the ARVC gene, 50 % heterozygous, and only 25% clear?  Are you going to eliminate 75% of the gene pool?  I hope not!

In this case, we will have to breed dogs with the gene, knowing we are producing more affected puppies each time we do.  If we breed affected to clear, we will have 50% affected, and 50% clear.  If we end up breeding heterozygotes together, again, we will maintain the 75 % affected, 25 % clear.  But there very well maybe scenarios where this would be a good decision for other reasons.

We then have to test the litters, and hopefully, because we are still breeding to the whole dog, not just the ARVC gene, we will find typey individuals with good temperaments, who are otherwise reasonably healthy, and also clear of the ARVC gene.  But, probably a lot of those who fit the other criteria, at least for a while, are going to be heterozygotes. 

So, there is a very large chance that, even after we have a genetic test for ARVC, we will still be breeding affected individuals, for quite some time.  *And doing so knowingly.*

I think this is what Virginia is talking about when she says our dilemmas might only increase once we have the genetic test. 

And, just think what we will have to do if we find 50% of the breed is homozygous for the ARVC gene. 

In other words, if all those other factors I mentioned above in my are true, as I suspect (dominant transmission, very common and widespread distribution of the ARVC gene), once we have a gene test, and find we have to breed affected individuals, this means we will have to knowingly produce affected puppies, if we are to save the breed.

The next dilemma is... what do you do with those puppies?

This is not an easy situation we are in, and we are fresh out of easy, black and white answers.  I think we will be for quite some time. 

Theresa Garton
tgarton@ix.netcom.com
Oklahoma City
http://www.WinmereBoxers.com

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