ATTENTION RR and TR Owners/breeders

Below is a statement from Swedish academics on Dermoid Sinus. This has been produced for clarification and is in response to the various queries forthcoming recently and in the light of recent publicity. Permission to cross-post. Searching on authors' names will reveal the research behind the statement.

Uppsala September 24, 2008





To whom it may concern



A statement concerning the genetic basis for the hair ridge and the congenital
malformation dermoid sinus in Rhodesian Ridgeback dogs



It has come to our attention that the recent World Congress of the Rhodesian
Ridgeback Association has left some uncertainty concerning the genetic basis for
the hair ridge and the dermoid sinus in Rhodesian Ridgeback dogs. We would
therefore like to clarify our views on this subject and its implications for
breeding.



1. The inheritance of the Ridge

All our data and all data we are aware of indicate that the ridge is inherited
as a fully dominant trait. The dominant allele causing the ridge is denoted R
whereas the recessive wild type-allele is denoted r. This means that a ridged
dog may either be homozygous (R/R) or heterozygous (R/r) for the Ridge allele
whereas all ridgeless dogs should be homozygous r/r for the normal allele. The
result presented in our Nature Genetics paper from 2007 (Hillbertz et al. Nature
Genetics 39:1318-1320) provided conclusive evidence that the mutation causing
the ridge in Rhodesian Ridgeback as well as in Thai Ridgeback dogs is a 133 kb
duplication on dog chromosome 18. [A duplication means that each Ridge
chromosome has two copies of this 133 kb fragment whereas a normal chromosome
has only a single copy. It is this doubling or duplication of the chromosome
region that constitutes the Ridge mutation.] So far all tested dogs with the
characteristic dorsal hair ridge have been heterozygous or homozygous for this
mutation whereas all ridgeless dogs we have tested lacked the duplication. The
duplication contains four complete genes (FGF3, FGF4, FGF19 and ORAOV1) and we
assume that it is the higher than normal expression of one or more of these
genes, attributable to their greater number, that leads to the development of
the hair ridge.



2. The genetic basis for dermoid sinus (DS)

DS does not have such a simple inheritance as the Ridge but our data clearly
showed that the Ridge mutation (i.e. the duplication described above) is the
major risk factor for the DS malformation in Rhodesian Ridgeback dogs. Most DS
dogs in our study were homozygous R/R (10 of 12) for the Ridge mutation but two
were classified as heterozygous R/r. However, DS or DS-like malformations also
occur in humans so it is possible that this type of malformation may occur in
dogs in the absence of the Ridge mutation. But its frequency in unridged
Ridgebacks should be as rare as it is in non-ridged breeds.



3. DNA tests

In our Nature Genetics paper we described a simple DNA test that can be used to
identify the presence of the Ridge mutation (the duplication). Any DNA
laboratory skilled in the art of DNA testing can perform this test and there is
no patent protecting its use. It is therefore easy to distinguish a ridged dog
(R/R or R/r) from a ridgeless dog (r/r) by the DNA test but we have not yet
established a diagnostic test that on a routine basis can distinguish animals
that are heterozygous carriers (R/r) from homozygous ridged (R/R) with 100%
certainty. The establishment of this test will require some further research.



4. Recommendations for breeding

The most straightforward way of reducing the incidence of DS in Rhodesian
Ridgeback dogs is to reduce the frequency of homozygotes for the Ridge mutation.
This can be accomplished by allowing the use of ridgeless dogs for breeding.
While we are aware that dogs with a DS are not usually kept for breeding,
matings between homozygous (R/R) ridged dogs (presumably without DS) and
ridgeless dogs (r/r) would give progeny all of which would be heterozygous
ridged (R/r) and therefore show ridging, and the incidence of DS would be low.
In matings between a heterozygous ridged dog (R/r) and a ridgeless dog (r/r),
50% are expected to be heterozygous ridged (R/r) and 50% are expected to be
ridgeless (r/r). In these matings no homozygous ridged progeny, which are the
major problem as regards the incidence of dermoid sinus, would occur. It should
therefore be possible to retain the ridge while keeping the incidence of DS to
its absolute minimum. It would be useful to develop a diagnostic test to
distinguish carriers (R/r) from homozygotes (R/R) because this would allow
breeders to avoid matings such as R/R x R/r that will produce homozygous ridged
(R/R) progeny.

It will of course be up to the individual breeders and to Ridgeback
breeding organizations to decide whether they prefer to keep the Ridge and
minimize the incidence of DS using the approach described above or whether they
would like to completely eliminate the problem with DS by allowing the Ridge
mutation to disappear from the population over time. If one decides to eliminate
the Ridge mutation it should not be done too quickly (during a few generations)
since that will lead to increased inbreeding in the breed as too many potential
breeding animals are eliminated.



Acknowledgement: We would like to thank Bruce Cattanach for valuable discussions
on this subject.



Leif Andersson1, Kerstin Lindblad-Toh1,2 and Göran Andersson3



1Department of Medical Biochemistry and Microbiology, Uppsala University, Box
597, SE-751 24 Uppsala, Sweden.

2Broad Institute of Harvard and MIT, 7 Cambridge Center, Cambridge,
Massachusetts 02142, USA.

3Department of Animal Breeding and Genetics, Swedish University of Agricultural
Sciences (SLU), Biomedical centre, Box 597, SE-751 24 Uppsala, Sweden.

I personally do not have any problem with ridgeless dogs being used to reduce the incidence of DS. I would have liked them to state the research being done with Folic acid and its effect on reducing the prevelence of DS.
I would not like to see the ridge being bred out of the breed.

Well looks like the culling of ridgeless pups is still possible, in spite of KC statements and protestations:

http://www.rhodesianridgebacks.org/

So the price of having a rr with a ridge is the death of those without...yet it is possible to breed away from it to a heterozygote...its a no-brainer...

Another example of weird and warped human 'thinking'

Yes, I had seen this and was so disappointed that they haven't stepped up and changed it, instead they would rather play with words.
I can only find one breeders website who has publically stated that they are not a member of the GB RR Club because of this - also disappointing.
Out of the other 3 clubs only one publically states they are against culling.
I agree, it is a no brainer