my chest and closed his eyes. He was baking hot and although he would respond a little if I stroked or talked to him, it was an effort. I knew it was time. I called the vet and Darwin
slipped away, ever so gently, before the needle was withdrawn from the vein in his leg. Of course, one rails against
the injustice of a two-year-old dog being taken by cancer. But we also felt blessed by this little man for both the pleasure he gave us and for the sheer joy with which he lived his last two weeks, away from the horrors of an Irish pound and whatever life it was that had led to him landing there. I tell this story because it is
easy to forget that crossbreeds can suffer from horrible diseases like lymphoma too, and not all cancer in purebreds is down to the inheritance of breed-specific cancer genes. But purebred dogs as a whole, according to one recent Italian study, do suffer twice as much cancer as their randomly bred cousins and some of these cancers are breed- specific - as are other canine health issues that we now think are the result of immune systems that have been compromised by inbreeding.
On the defensive Our immune system is why we
don’t die of a cold or the tiniest of scratches. It is probably the case that all living beings get cancer every second of every day; it’s just that our immune system stamps on it. It is our own personal army of sentinel soldiers who are on the lookout for any breach of our defences. Once spotted, a counter-attack is launched to repel the invader - be it bacteria, virus, parasite or cancer. An optimum immune system
has a large armoury of diverse weapons - different genes - primed to take on the enemy. Inbreeding, however, reduces the number of different weapons at the immune system’s disposal because related individuals are likely to be genetically very similar. It’s a bit like nature’s version of scissors-paper-stone. A mating between close relatives could easily result in a double dose of scissors - making the progeny invincible against paper, but pretty damn useless against stone.
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Inbreeding affects the
immune system in another way: it reduces the ability to distinguish ‘self’ from ‘enemy’. And that can be deadly. The Tasmanian Devil, for instance, is being decimated by an infectious cancer that the small marsupial’s immune system simply doesn’t see as a foreign invader. Likewise, the immune system might suddenly start attacking its own tissues, wrongly identifying them as an enemy. The result is autoimmune diseases, such as Addison’s disease, atopy, hypothyroidism and different forms of inflammatory disorders. There is some good news,
though. Finnish and UK university scientists in collaboration with a private company, Genoscoper, have worked out how to test a key part of the genome involved in coding our immune systems - an area that scientists call the ‘major histocompatibility complex’. (A bit of a mouthful even for them, though, so it’s shortened to ‘MHC’.) For £150, you can send off a mouth swab from your dog to the Genoscoper lab in Helsinki and back will come a list of the ‘haplotypes’ that make up a part of your dog’s MHC. What’s a haplotype? It’s
simply a bunch of linked genes that are inherited as a group. Just like with single genes, you have pairs of them - one inherited from each parent. It’s been found, for instance, that Salukis have at least 24 different haplotypes across the breed as a whole. Nova Scotia Duck Tolling Retrievers, however, have only five different haplotypes at their disposal in the part of the MHC that Genoscoper tests. Some haplotypes are
associated with specific diseases, but, in general, the more haplotypes there are in the breed, the better. In other words, you’d expect Salukis
to be healthier than Tollers. And, indeed, that’s the case. Tollers suffer from a number of serious immune-mediated problems, notably systemic lupus erythematosus (SLE) and a rheumatic condition named after the breed - Toller disease. In Bearded Collies, only
seven haplotypes have been found and they too suffer a lot of autoimmune problems, including symmetrical lupoid onychodystrophy (SLO), which affects the development of the dog’s claws.
Numbers game Whippets, meanwhile, have been
found to have 13 haplotypes and are, generally, considered a rather healthier breed. There are two ways in which
the Genoscoper test could be a real help. First, it can be used to get an overall measure of the MHC diversity of a breed. Fifteen forward-thinking breed clubs have already done this, and, as word spreads, many more are considering it. It’s not cheap because Genoscoper needs 50-100 DNA samples for each breed at a cost of £150 per swab (although Genoscoper will discount for larger numbers). But the result is a genuinely useful benchmark that breed clubs - and perhaps kennel clubs too - can use to help guide them in planning overall breeding strategies for a breed. It’s already known, for instance, that some haplotypes are much more common than others. Identifying and breeding from dogs blessed with rare haplotypes could bring in some much-needed diversity to a breed without the need to outcross to a totally different breed. The second way the
Genoscoper test can help is by giving individual breeders a way to produce puppies with the strongest possible immune systems. How? Well, let’s say a breeder has narrowed the choice
of stud dog for her bitch down to three great possibles. The Genoscoper test will allow her to choose the one that has the most different MHC haplotypes - and also allow her to avoid doubling up on haplotypes that are associated with particular health issues (such as SLE in Tollers and SLO in Beardies) in much the same way as a standard DNA test. In fact, studies show that dogs that inherit identical haplotypes from each parent - even if those haplotypes are not associated with a particular problem - are at an increased risk of autoimmune disorders. Ironically, the Genoscoper
test will never help randomly bred dogs like sweet Darwin, the victim of an unlucky throw of the dice. And there is much more to understand about how our dogs’ immune systems work - and particularly how it interacts with other genes. Undoubtedly, the MHC plays a big role in how dogs deal with various disorders, but it is not the whole story. Even the strongest immune systems may not be able to cope if the genetic dice are really loaded, or if the environmental onslaught is just too great. But I love the idea of the Genoscoper test and the hope it offers. Geneticists warn us that
it will be impossible - and indeed not always desirable - to eradicate all dodgy genes from our dogs, even if it was possible to identify them all. So what a wonderful idea it is to approach it from a different angle: to boost our dogs’ immune systems so that they are better able to deal with the various onslaughts that life and genetics throw at them - including those diseases for which, at present, there are no DNA tests.
Visit
www.genoscoper.com for more information on Genoscoper’s DLA Diversity Test
Jemima Harrison is a journalist/TV producer best known for making Pedigree Dogs Exposed, the BBC1 film that highlighted health and welfare problems in pedigree dogs. Jemima owns a working Flat Coated Retriever and several crossbreeds. Passionate about dogs, she also runs a small independent rescue specialising in finding homes for retriever crosses
Dogs Today August 2010 BLACK & TAN | FALL 2010
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