Disproportionate Dwarfism in Vizslas

This article by guest contributor, Emily Ansel, DVM, first appeared in the January – March 2023 issue of The Vizsla News.

Breeders have an almost unending list of considerations when breeding a litter, not the least of which is knowing, or trying to figure out, what potential health issues might be lurking in a dog’s pedigree. Disproportionate dwarfism used to be one of these “untestable” problems that weaved its way through generations of healthy Vizslas only to pop up unexpectedly. Litters with one or two affected puppies have been reported first-hand by breeders since at least the 1970s; however, the incidence has been low enough that many people are unaware of its existence in our breed.

In 2021, we were extremely fortunate that VetGen and the canine genetics laboratory of Dr. Tosso Leeb, Director of the Vetsuisse Institute of Genetics at the University of Bern, decided to begin the search for the genetic cause of disproportionate dwarfism in Vizslas. Utilizing samples provided by multiple dedicated breeders and owners, and whole genome sequencing, a causative mutation was identified. This same mutation was confirmed present in other unrelated affected dogs and parents of affected dogs. The pedigrees containing this gene are vastly different, including pedigrees that we would characterize as show, field, backyard, and puppy mill bred. This wide distribution suggests that the gene has been present in the breed for a very long time.

As 2022 comes to a close, we have ability to test dogs for carrier status to avoid producing affected puppies, and a detailed scientific article on the condition has just been published. I am so happy for our collective incredible good fortune and lasting advancement in breed health.

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To order your test for Skeletal Dysplasia 3:

https://www.vetgen.com/ordertests.aspx?id=Vizsla

Note from the VCA: Upon submission, please consider releasing the results to OFA by paying the extra small fee. Only by building the database of information can we, as breeders, continue to make informed breeding decisions for the future.

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Ok, but what does this all mean exactly?

Disproportionate dwarfism is a type of skeletal dysplasia (aka osteochondrodysplasia) – abnormal growth and development of the bones. The term disproportionate dwarfism indicates that the limbs are shorted while the head and body remain normal in size. While proportionate dwarfism indicates all parts of the body are affected, resulting in a normally-proportioned but overall smaller individual. Based on current naming schemes, and consultation with experts in the field, the research group termed our Vizsla condition “skeletal dysplasia 3.” The gene affected in Vizslas is different from the ones in other breeds; thus, you may have seen other DNA tests for dwarfism, but none of them applied to Vizslas previously.

Affected adult Vizslas in our small study ranged from 16.8 to 20 inches, which, unsurprisingly, is significantly shorter than unaffected dogs. The upper arm (humerus) and upper leg (femur) bones are the most shortened, but a thickened/knobby appearance to the wrist (carpus) is also striking, especially in puppies and young dogs. Anecdotally, affected dogs seem to be otherwise healthy and live normal life spans.

This condition is autosomal recessive, making it easy to predict the results of a breeding. To produce an affected puppy, both parents must be carriers.

Clear x Clear = 100% Clear

Carrier x Clear = 50% Carrier, 50% Clear

Carrier x Carrier = 25% Affected, 50% Carrier, 25% Clear

Skeletal Dysplasia 3 Frequently Asked Questions

–Should we stop breeding all carriers? My short answer is no, but I respect that others may differ. Carriers have been bred for decades, and I would wager that the majority of carriers never produced an affected puppy, making them very hard to identify until now. Many, many of our current dogs are the result of a carrier breeding at some point in the past. My interpretation is that carrier breeding can be done responsibly and ethically with a “breed and replace” goal. Breed the carrier to a confirmed clear mate to ensure no affected puppies. Test all puppies for clear/carrier status prior to placement, and “replace” your carrier in the breeding pool with one of its clear offspring.

–How do you test? A cheek swab is most common, but other samples may be used (ie blood, semen, etc.) Docked tails are not preferred.

–How soon after birth can I test puppies? Since DNA is the same from birth, you may take the sample as soon as you are comfortable putting the swab into the mouth. We recommend isolating the animal(s) for one hour to prevent cross-contamination of DNA. (taken directly from Vetgen website)

–Where can I check out the scientific article? The December 2022 issue of Genes: https://www.mdpi.com/2073-4425/13/12/2354 . This is an open access journal.

Key Points about Skeletal Dysplasia 3

–In this initial study, the frequency of carriers was 11.6% among 95 dogs who were NOT parents, full-siblings, or half-siblings of the affected dogs. The true frequency among all vizslas is likely lower, as demand for early testing was higher among those whose dogs have known carriers in their extended pedigrees.

–Resist the urge to place blame; this gene has been around since long before most of us owned Vizslas. When cases were few and far between (or never spoken of), it wasn’t clear whether this was genetic or a random occurrence. Although we all love a good pedigree, the fact is, we don’t need to guess or base decisions on rumors or inside knowledge. We can easily test and have definitive answers about the genes at play in any one dog. Thanks to all the breeders and owners who are willing to share and put the health of the breed first – you made this test possible!

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