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Multifocal Retinal Dysplasia (MRD)

Background

This has only recently become evident in our breed and thus far has only occurred in one, non-accredited, bloodline. It appears to be as a result of prolific, ill-advised inbreeding/line-breeding resulting in other serious conditions also affecting the line (sadly two affixes are actually affected at present).

The British Veterinary Association (BVA) have advised that the only way to eradicate MRD is to implement annual eye tests, for studs and broods, AND litter screening as the condition can be apparent at birth then dissipate during maturity, giving an affected dog a 'clear' eye certificate. As all our Utonagan are related to each other in some way (due to the small gene pool) we feel the discovery of this latest condition further compounds the need for new blood to be injected into the breed, as agreed at the 2006 AGM. A report and voting form on New Blood has been sent out in the latest newsletter and will be available soon in the members area too.

MRD is a serious hereditary eye disease, as listed on the BVA schedule, and may lead to blindness in the affected dog; therefore TUS are not taking it lightly and neither do KC breed clubs. Some dogs may have no visual impairment and others may be severely visually impaired. There are three differing types of the disease in the following range:

1. Type 1 - The mildest form. Retinal folds or rosettes (lesions including rosette formations, linear folding of the sensory retina and vermiform linear streaks). In very mild cases the folds/rosettes may disappear with age, but may also increase. Thus, with so many of our dogs related, type one is still to be considered deleterous to our remaining gene pool.

2. Type 2 - Geographical changes, i.e. disorganisation of the retina, thinning and irregularly shaped areas of retinal dysplasia, often with an associated limited region of retinal detachment. This will cause some visual impairment or blindness throughout the dogs life

3. Type 3 - Retinal Detachment. Severe disorganisation of the retina where the retinal layers actually detach. The affected dog will be blind. This can happen very suddenly, which is obviously very distressing for dog and owner. The BVA advise all affected dogs are re-tested annually.

Retinal Dysplasia has been linked to other forms of Skeletal Dysplasia (i.e. hip/elbow) in several breeds of dog; there is circumstantial evidence that such a link could be apparent in this Utonagan line.

All types listed above are present from birth.

 

The dogs proven to be affected so far (BVA certificates received) are all related; Mother and 5 offspring out of 10 (one stillborn, 9 raised). There is another related bitch also affected, she is thought to have Total Retinal Dysplasia as she went very suddenly, completely blind. She did regain partial vision and we are awaiting a BVA certficate to confirm her condition. Most of the affected pups had folds (see description of form 3 MRD on BVA website/in BVA pamphlets) at six weeks of age. One (now a non-TUS-accredited stud dog) tested affected still at 21 months of age, wheras his sister (a non-TUS-accredited brood bitch) who also had folds at six weeks, tested clear at 12 months.

Against our advice, a second litter has been produced from the same dam and we are advised that six of the surviving seven pups (11 born) have been found to be affected with MRD; however we still await a copy of the second litters eye results.

 

Though it has not been scientifically proven - to do that the Animal Health Trust need as many DNA samples as possible of affected AND unaffected dogs, contact a committee member for further information - the litters quoted above seem to fit the pattern of Recessive Inheritance; see the following excerpt.

"The recessive inheritance pattern has the following characteristics:

  • Male and female offspring are affected equally.
  • If both parents are unaffected but heterozygous for the trait (Carriers), each of their offspring has a one in four chance of being affected.
  • If both parents are affected, all of their offspring will be affected.
  • If one parent is affected and the other is unaffected (Non-carrier). all of their offspring will be unaffected, but will carry the defective gene.

If one parent is affected and the other is a Carrier, half of their offspring will be affected."

With half the pups affected, from an affected Dam and unaffected Sire (no certificate provided), it can be fairly safely assumed that the Sire is a Carrier. Regardless, all the unaffected pups from both litters will be Carriers if the trait is typically recessive, as that would make their mother homozygous for MRD.

Causes

See the links below. In most cases of MRD it is determined to be hereditary, but in lines shown to be unaffected it may also be caused by pre-natal exposure to: the Herpes, or possibly Parvo, Virus'; radiation during scans/x-rays or a Vitamin A deficiency. None of these were reported or evident in either of the afore-mentioned litters.

Because the Utonagan so far known to be affected are all closely related and/or line-bred with past instances of inbreeding, we are of the opinion that MRD is hereditary in the affected Utonagan lines.

Diagnosis and Tests

This disease can be missed on a routine veterinary eye test, therefore all dogs should have a full BVA eye screen, whereby one of the BVA' qualified Ophthalmologist panellists will thoroughly examine your dogs eyes. The dog is also tested for all other known hereditary and congenital eye defects. making it all the more relevant. Moreover it is the least expensive test (£32 per test/year), is completely painless to the dog and will only take about 40mins all in.

Treatment

Unfortunately there is no known treatment or cure for this disease at present. Obviously an affected dog will be extremely distressed if it suddenly becomes blind, however this should not be the prevailing outcome. Sadly we will just have to wait for reports to come back as the affected dogs get older as to how severe their visual impairments are/become.

Breeding Advice

Obviously, as with any other inherited disease, no affected dog or bitch should be bred from. TUS already stipulate that all studs and broods must achieve clear eye test certificates before mating, however - as mentioned earlier - this condition has brought to light the importance of having all Utonagan litters eye tested before they leave the breeder. It is preferable that all Utonagan are eye tested yearly anyhow, though at the very least if any pups are found to be affected with MRD their entire litter should be tested again at 12 months. This will help us enormously to create a clearer picture of the long-term prognosis of this disease.

Regardless of the results at 12 months of a pup affected with MRD at birth, she/he should NOT be used for breeding as he/she clearly carries the condition. In a perfect world their siblings should not be used either, but with our extremely limited gene pool it may be considered if the unaffected carrier is of superb type. Naturally, such a dog could only be put to a line clear of MRD and as unrelated as possible.

Occurrences within the breed

Sulin, Kaharec

Links

Below are a few links from the BVA and several different breed associations, all giving good reasonsconcerning the importance of annual eye testing for all breeding stock, and for litter screening particularly with relevance to MRD.

http://www.bva.co.uk/public/chs/chs/_eye_procedure.pdf

In this link from the BVA website please note in particular the headings 'Important Inherited Eye Diseases', 'Need I Be Worried' and 'Eye Testing Success' clearly showing why eye testing is needed.

These are some very informative links giving detailed information about the disease, it's causes and effects.

http://www.provet.co.uk/Petfacts/healthtips/retinaldysplasia.htm

http://server.vet.cam.ac.uk/FMPro

http://journals.tubitak.gov.tr/veterinary/issues/vet05-29-2-54-0402-33.pdf

http://en.wikipedia.org/wiki/Retinal_dysplasia

http://www.upei.ca/cidd/Diseases/ocular%20disorders/retinal%20dysplasia.htm

http://www.samoyedhealthfoundation.org/diseases/retinal-dysplasia-folds