PRA-CRD4/cord1 is a retinal disease that causes progressive, non-painful vision loss. The retina contains cells, called photoreceptors, that collect information about light and send signals to the brain. There are two types of photoreceptors: rods, for night vision and movement, and cones, for day vision and color. This type of PRA leads to early loss of cone cells, causing day blindness before night blindness.

Before reading further, you should know how this condition affects our breed specifically.  Out of the thousands of American Bullies who have carried this variant, none have been affected by it!  Many researchers believe that CRD4 does not affect our breed.  Some researchers also believe that more than 65% of all American Bullies have this condition.  Some DNA testing companies have even decided to not even test it for our breed, proving further that many scientists do not believe it affects our breed at all.

1 variant vs 2 variants: It is important to know that there is a major difference whether your dog has 1 or 2 copies of the variant.  If you dog has 1 copy, then it is strictly a carrier... It cannot and will not affect the health of the dog what-so-ever.  If you dog has 2 copies, then they are "affected" and normally would cause your dog to be affected by the disease.  Fortunately, like we mentioned above, dogs with 2 copies have not been affected at all.  Some of these dogs are now over 12 years of age.  Again, not one case has come to show that CRD4 affects American Bullies in any way.

How 1 variant vs 2 variants affects breeding:  Below is a chart that will show you what will happen if you breed a dog with 1 variant, 2 variants or even if it is 100% clear of the condition.

What is MBK doing about this?  Great question!  MBK is always trying to be the leader when it comes to anything moral or ethical in terms of breeding and doing business in general.  There has been a lot of discussion among breeders, and many other breeders have chosen to ignore CRD4 results because it has not been shown to affect our breed.  MBK has decided to do our absolute best to clear our stock of this disease within a couple of generations.  All of our dogs have been DNA tested, and some do carry this genetic trait.  If any of our dogs is a double-carrier, they will only be bred with a dog that has been cleared.  This means that we will work to eliminate this from our stock 100% within a few generations of breeding.  We do not fault any other breeders who have decided to ignore the results, as this disease has not shown to affect any of our breed... But this is still very new, and we would rather err on the side of caution.  Could this change as scientific results and research come forward?  Yes.  But as of right now, this is the decision we have made.

DNA testing your dog is very important in this day and age.  MBK has been the leader in this department, and we will continue to be as open and transparent as possible with our customers; along with educating them about how DNA testing works and how it can affect them and their dogs.

UPDATE 04/02/2022:  MBK continues researching.  We've been in contact with the scientist/research who discovered CRD4.  With our many email communications going back and forth, it has been expressed to us that they believe CRD4 does not affect our breed.  They believe there is a modifier gene named MAP9 that needs to also be present in order for CRD4 to affect a dog, and that gene has never been seen in our breed.  We've passed this information over to Embark, who has communicated back to MBK and has now publicly stated the following quote:

  • Based on current research, the PRA crd4/cord1 is not known to affect American Bullies.

MBK will continue educating ourselves and working with the relevant scientists and researchers in case there is any further information.  If there is, we will update our website accordingly.