I first heard mention of it here: Dog Coat Colour Genetics CDA does not occur on all dilutes and its frequency varies between breeds. It is particularly common in Dobermanns, occuring in up to 80% of dilute dogs. Dilutes in other species such as mice are caused by the same gene, and yet CDA is not known in these, implying it is not an unavoidable consequence of dilution. It is thought that CDA may be caused by a specific dilution gene - labelled dl. Just as there are various different b alleles that all cause the liver colour (phenotypically the same, so only distinguishable through genetic testing), it is probable that there are a number of different d alleles as well, and only one of these causes CDA. Technically this makes CDA a recessive allele, as it is recessive to D (non-dilute, non-CDA) however dl is most likely dominant over the standard d allele.
I finally had an chance to go read these sites--thanks so much for including them--I think from what I read that the existence of a dl gene remains pretty speculative.
Which was corroborated by this article hosted on the DPCA site: https://www.dpca.org/BreedEd/article...ution-alopecia A third allele (dl) which is associated with CDA has been proposed.6 While this is a long way from being proven, it could help explain why some dilute animals are unaffected. Dogs with a genotype dd would be normal coated dilutes, ddl would be intermediates (mildly affected?) and dldl would be CDA affected. A genotype of Ddl should represent deeply pigmented dogs which were carriers of CDA.
The DPCA Breeders Education article also uses the word "proposed" and goes on to note that "this is a long way from being proven,"
I lost a bunch of reference sites when an old computer basically gagged and died--eating the contents of its hard drive in the process. As far as I remember all of them who had information about possible genetic causes for CDA in the Doberman pretty much echo'd the fact that the possibility of a multiple d allel's incuding a defective dl were speculative.
I couldn't either, but genetics has come such a long way since the original 1990 study, although I'd like to have been able to read it I'm not sure that much of its information may have been superceded by now.
There was a vet dermatologist who some years ago was sure that he had the answer to red Dobermans who had follicular dysplasia--or rather the cause of it in red Dobermans. He was certain that it occured because they carried dilution. At that time there was no way to prove or disprove his theory because there was no gene test for dilution and most of us who had been in Dobes for any length of time knew of cases where, being the recessive that it was dilutions could lie hidden for generations. But ultimately that vet had to give up his theory (of course it was a study of only one case--and you could argue that the n was too small to prove anything) when a red Doberman he had dxd with follicular dysplasia secondary to carrying a dilution gene got tested for dilution when the gene test was released and the dog turned out to NOT carry dilution.
Fair enough! Conjecture about d(l) could very well be some sort of association between d and this other gene, like with (pre-LUA) dalmatians and HUA: it's not that the gene for spots caused HUA but that all genes for spots were associated with HUA. I guess I'll have to wait and see what the science ends up being in another ten or twenty years!
Yeah, me too--but I've waited this long, so maybe I'll actually live long enough for the folks who do this stuff to figure it out.
<vbg> I'll leave you with another one to contemplate though--I've seen a very few old dilute dogs who had perfect coats right up the time they died--really very few--one blue and two fawns. And I've heard about a few more that I never saw--very few. And I know a vet, who, when she was still in vet school did a very elaborate study and produced a paper on CDA in dilute Dobermans. We talked about her paper and what she found several times and the thing I remember best was the fact that while she found some dilute dogs with good coats she said you'd never want to try to produce dilute Dobes with good coats from them. She said that they so little resembled a Doberman that if she hadn't seen the AKC registrations and pedigrees (some that went back 8 and 10 generations) she'd hardly have believed they were Dobe--but they did have great coats--the old dogs and the young dogs.