Deafness and Ridge DNA Tests...Coming Soon! 

The Rhodesian Ridgeback Club of the United States is pleased to announce that two genetic mutations affecting the Rhodesian Ridgeback have recently been found: for deafness and the ridge.

Details on the DNA tests will be posted here as soon as they are available, so please check back often.

Ridge

Ridgeback breeders have long surmised that the ridge is likely a simple dominant trait. The mutation that causes the ridge was recently found by a consortium of researchers at the Swedish University of Agricultural Sciences (Nicolette Salmon Hillbertz, Goran Andersson, et al), Uppsala University (Leif Andersson, et al) and the Broad Institute (Kerstin Lindblad-Toh, et al).

The scientists found that the ridge results from a duplication of a region in the genome that contains genes for the fibroblast growth factor (FGF), which play a crucial role in development. The ridge mutation leads to a defect in the planar cell polarity system, which is needed for both the normal orientation of hair follicles and for neural-tube closure.

The study also found that Ridgebacks with two copies of the dominant ridge mutation were at a higher risk of developing the congenital health defect dermoid sinus than those with just one copy.

Click here for an explanation of how ridge genetics works.

 

Heritable Deafness

Mark Neff and his team of researchers at the University of California at Davis have located the mutation that causes this breed-specific defect in the Ridgeback.

Here are some Frequently Asked Questions (FAQs) about this disease.

 

Q. How common is deafness in the Rhodesian Ridgeback?

While it is not widespread, deafness is also not a rarity in our breed. It seems to occur in pockets of the breed population. We will soon  have a direct marker test that, if used properly, can guarantee that breeders never produce a deaf Ridgeback. 

Q. Is deafness in Ridgebacks the same as deafness in Dalmatians?

A. No, it is very different. In Dalmatians and other breeds with white markings, deafness is connected to the presence of white. By contrast, deafness in Ridgebacks is not related to color – what geneticists call “non-syndromic.”

Q. Can deafness be diagnosed with a BAER (brainstem auditory evoked response) test at 8 weeks old?

A. Unfortunately, not always. Deafness in Ridgeback puppies is progressive, and many deaf puppies are hearing at 8 weeks. They begin to go deaf soon after, and from the information we have available, all are bilaterally deaf by nine to 12 months, if not sooner.

Q. How is deafness inherited in Ridgebacks?

A. Deafness in Ridgebacks is a simple autosomal recessive – that is, two non-deaf dogs that each carry the gene for deafness can produce deaf puppies if bred together. In such carrier-to-carrier breedings, each puppy has a 25 percent chance of becoming deaf.

Q. How can I guarantee that I never produce a deaf Ridgeback?

A. Thanks to the invaluable cooperation of some dedicated Ridgeback breeders and owners, researchers at the University of California at Davis have isolated the genetic mutation that causes deafness in the Rhodesian Ridgeback. They are now in the process of creating a simple cheek-swab test that can identify which dogs are carriers for deafness.

Q. What combinations produce deafness?

A. Breeding two dogs that are carriers (even if they themselves can hear) will eventually produce deaf puppies.

Breeding carriers to non-carriers will NOT produce deafness.

Q. So can deafness carriers be bred?

A. Yes, as long as they are bred to dogs that have a non-carrier, or clear status, confirmed by the future marker test.

The only time deafness results is if two carriers are bred together. A carrier bred to a non-carrier will produce all hearing offspring, though a percentage of the offspring will be carriers themselves.

Q. Can the offspring of carrier-to-non-carrier breedings be bred?

A. Yes, certainly, with the proper testing. Breeders will have to perform the direct-marker test on any breeding stock resulting from the carrier-to-clear breeding. If the offspring is clear, it can be bred to any other dog, including a carrier. If the offspring is a carrier, then, like its parent, it can only be bred to a clear dog.

The ultimate purpose of using genetic marker tests is for breeders to eventually replace carrier breeding stock with non-carriers. But if the best, soundest, most typey dog in the litter is a carrier, then it is certainly ethical to keep that dog and breed it, provided that any dog that it is bred to is a non-carrier, as confirmed by the direct-marker test. 

Q. What dogs should be screened with this direct-marker test?

A. Every Rhodesian Ridgeback in a breeding program should have its deafness status established with this genetic test once it is available, which should be sometime in 2007.

Q. I have never had deafness in my line. Why should I have the direct-marker test done on my dogs?

A. Because the direct-marker test is the only definitive way to know if your dog is a carrier or not. Recessive traits like deafness can snake through a pedigree for many generations before surfacing. The direct marker test is 100 percent accurate. Why allow for even a sliver of uncertainty with a disease as serious and devastating as deafness?

Q. How much does the test cost?

A. The direct-market test will be offered by VGL, the laboratory at the University of California at Davis. While details of the test are still pending, most similar tests at the lab cost in the $40 to $60 range.

Q. If both the sire and dam of a puppy test clear (i.e., are non-carriers), won’t all their offspring be clear? And if so, do I need to retest?

A. Yes, the offspring of clear-to-clear breedings will all be clear, and do not have the potential to produce deafness no matter who they are bred to.

However, for the time being, we are encouraging breeders to formally submit tests on such presumed clear offspring.

Very preliminary discussions with other breed clubs that have been using similar direct-marker tests has made us aware of issues that can compromise the “cleared status” of offspring, such as mistaken parentage (i.e. a different sire than the one that was tested). This has led to some presumed clear puppies in fact being carriers.  

At this early point in the process -- and until we thoroughly investigate the pitfalls and find reasonable solutions to these concerns -- we recommend that offspring not be presumed clear unless they have been tested themselves. We recognize that this incurs a nominal cost for the breeder, but think that the peace of mind is well worth it.

Q.  Are there any other kinds of deafness in the Rhodesian Ridgeback?

A. As far as we know, the bilateral (two-ear) deafness caused by the genetic mutation found by the UC Davis team is the only deafness in the breed. We have run across a handful of dogs with unilateral (one-ear) hearing loss in the breed, but thus far there is no evidence to suggest that it is related to the bilateral deafness caused by this genetic mutation. 

In dogs, there are many different kinds of deafness caused by various genetic mutations. But at this time, there is no indication that any other form of heritable deafness occurs in the Rhodesian Ridgeback.

Q. I test all my breeding stock with BAER testing. Is this necessary now?

A. Not once the direct-marker test is made available. Because the test can tell us the genetic makeup of the parents, it essentially renders BAER testing obsolete for those dogs whose parents have been tested.

Q. Where can I find more information on the direct-marker test’s availability, or get answers to more questions I have on deafness breeding protocols in Ridgebacks?

A. Updates will be available on the home page of the RRCUS Health & Genetics web site at www.RhodesianRidgebackHealth.org.

You can also contact Health & Genetics Chair Denise Flaim at revodana@aol.com or (516) 676-3398.

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