Kidney Disease and DNA Swabbing

Maud Hawkes (2010)

BSc(Hons) Animal Science

The Skye Terrier is generally a fairly healthy breed, but it is also an endangered breed due to the decline in numbers and continuously shrinking gene pool. This is a global phenomenon and if pedigrees are studied it can be seen that Skyes around the world share many common lines. Any new or existing genetic problem might hence potentially have an effect on the whole breed population. It is, therefore, of uttermost importance to monitor the health of our wonderful breed with vigilance.

A DNA collection was started 2006 as a tool to guard over the future health of the breed. DNA should be submitted from all puppies before they leave the breeder’s premises, in accordance with the Skye Terrier Club’s (STC) Code of Ethics (27). Case histories and test results are being submitted to the Skye Terrier Health Committee and held on a breed data base, with owner- and dog identity treated as strictly confidential information. A yearly Health Report is also issued listing the conditions that have been reported during the year gone by (health reports from 2007 to 2012 are available on this site, under the Breed Health menu).

The 2010 Health Report and the actions put into place following it seem to have resulted in some controversy and queries. It has, therefore, been found important to address some of those issues here.
Further sad deaths from Renal Dysplasia, together with a number of dogs diagnosed with suspected polycystic kidneys (PKD), did lead to a decision to suggest that another health screening tool in the form of ultrasound scanning of breeding stock would be beneficial in trying to keep the breed as healthy as possible. This had indeed also been suggested by a number of veterinary practitioners and is also in line with breed health strategies suggested to us by geneticists at the Kennel Club and at the Animal Health Trust (AHT). Both the KC and AHT emphasize how important it is for breed clubs to try and build up a picture of the whole health situation in their breed and to employ all available health screening tools, e.g. DNA testing, ultrasound scanning, eye examinations, blood tests etc., for this purpose. They also encourage the breeders to be as open as possible and to recognize that many conditions are more prevalent than people think.

It has to be understood that nobody is to blame for cases of inherited conditions. It also has to be noted that if 1% of the dogs in a population are affected with a condition inherited in a recessive mode, then 18 % of the dogs in that population can be expected to be carriers of the disease-causing gene. ‘Bad’ genes are present in all forms of life but we do now at last have the tools of science to deal with them in a mature way.

The requirement of compulsory scanning of breeding stock has not been brought in without taking “expert advice”. Blood tests can be useful for monitoring and treating conditions in affected dogs, i.e. in management and prognosis, but have no value in initial diagnosis, since roughly 75% of kidney tissue has to be lost, before impairment can be detected. They will be normal in a dog where the kidneys are still functioning normally and give no insight at all into any structural changes. Consideration for the optimum age of scanning has not been neglected although it must be said that it is difficult to be precise regarding optimum scanning ages when dealing with conditions where no previous research has been undertaken in the breed. PKD in Persian cats can be detected from as early as 8 weeks, but the lower age limit agreed for certified scans is 10 months of age; the lower age limit set for Bull terriers is ~12 months (although cases have been detected from as early as 6 weeks); and Renal Dysplasia in Cairn terriers has been detected by ultrasound at an early age and long before the onset of clinical or laboratory evidence of renal failure.

It was decided, for the time being, to limit the requirement for ultrasound scanning of Skye terriers to breeding stock. No Bitch must be bred from before the age of 12 months (KC regulation) and the STC’s Code of Ethics (17) recommends 24 months. There is of course no breeding age limit applied to dogs but they obviously have to be sexually mature and, therefore, no longer puppies. ‘Breeding stock’ must therefore be understood to mean dogs old enough to be bred from (puppies can only be regarded as potentials).

It has been pointed out that, for cats, there is a list of vets approved for scanning. PKD is unfortunately a very common condition in some breeds of cats. There is, however, a very large number of those cats, thereby both practically and economically facilitating research. The Bull terrier breed, which is in a much more comparable situation to ours, does not have such a list. Their owners/breeders instead rely on the fact that many veterinary surgeries now have excellent scanning equipment and skilled staff.  This has been found by the owners to be the easiest and most cost effective way to have a primary scan undertaken. Any abnormal scan is followed up by re-scanning at a referrals specialist or one of the veterinary schools to verify the initial results. This method has proved successful for them and is also the one The STC have adopted.

It was explained at the 2010 AGM that this was the sequence of action to be taken. This is the course of action followed at the present time and it will be continued until the method has been disproved or better alternatives have appeared. Strategies can never be static but must always be influenced by new findings.
It has to be understood that the demand for a ‘renal expert’ is somewhat misguided. Veterinary schools do not have the equivalent of Urological departments in Human medicine. The vets dealing with kidney related problems in dogs typically belong to the department of Small Animal Internal Medicine (although researchers from other faculties may also be involved, as can easily be substantiated if journal articles are studied).

Facts and results have to be gathered, as advised by the AHT, before a strong link can be formed with an institution or potential researcher. Work on this is however ongoing through communication with representatives from the veterinary profession. It is also, at this stage, not possible to assess any future or potential costs. Enough clinical data and DNA samples have been collected before any research can be considered and then funding applied for.

The DNA collection started as late as 2006 but we are now also receiving samples from affected dogs and their relatives from abroad. Work is being undertaken on further international co-operation and the Skye Terrier Club of Finland has recently decided to launch a DNA scheme, with the samples being added to those held here at the AHT.

A couple of ‘ring-side’ myths also seem to have been circulated and have to be dispelled.

(1)  Kidney problems are caused by bad feeding/rearing

There is certainly no scientific evidence of such a thing whatsoever and it can be presumed that millions of cat- and dog breeders around the world would be up in arms at the mere suggestion. Renal dysplasia and polycystic kidney disease are both example of structural defects that are genetically inherited. They are not caused by environmental factors (although the diseases can be exacerbated by such factors).

(2)  Renal cysts could be caused by ‘worms’

The same sentiment as expressed in relation to (1) does of course apply to this too but it can be presumed that this theory refers to hydatid cysts. These are indeed nasty cysts lodging preferably in the liver, but also elsewhere. They are caused by the tapeworm Echinococcus granulosa. The major problem with this theory is that the cysts are only present in the intermediate host, usually sheep. The dog (or other canids, e.g. fox) is, however, the definitive host and doesn’t develop cysts – they develop tapeworms that shed their ‘eggs’ on the ground. The shed eggs are then eaten by the intermediate host, the sheep, who then develops the hydatid cysts.