SD2 Skeletal Dysplasia Type 2 in the Labrador
Short legged but healthy dogs
My SD2 Affected Yellow Lab Connie next to Monty, an unaffected Drakehead Lab
SD2 gene mutation aka Skeletal dysplasia type 2 or inherited dwarfism in Labradors is an abnormality of skeletal development that causes short-leggedness in Labrador Retrievers.
It has no clinical effects, causes no health issues and has no adverse effects on long term health or longevity.
We have all seen 'shortie Labs' those normal looking Labradors with legs like basset hounds or in my own Labradors case (pictured above) she looks like a giant Corgi.
This genetic mutation has only been observed in Labrador Retrievers of working lines (as opposed to show lines) and has been traced back to 1966 where one specific champion working dog was bred from multiple times
As the working Labrador bloodlines have been crossbred numerous times over the decades (a check on your Labradors ancestry will show how many common ancestors the Dam & Sire of your dog have), it is quite common that 2 dogs carrying the mutated gene will be mated.
SD2 is very common and It is becoming clear that some of our top Field Trial Champions in the UK were most probably carriers of SD2.
The gene has autosomal recessive inheritance (both parents have to have copies of the mutated gene), whenever 2 dogs who have inherited the SD2 gene from this common ancestor produce a litter some of the puppies will develop short legs.
From the University of Bern web site:
Skeletal dysplasia 2 (SD2) is a mild form of skeletal dysplasia that was recently discovered to affect Labrador Retrievers. The phenotype (appearance) manifests as short legs in combination with normal body length and width. Affected dogs typically have forelegs slightly more affected than hind legs, and a low shoulder height (<50 cm) compared to the international breed standard (54-57 cm).
Skeletal Dysplasia Type 2 is different from several other skeletal dysplasias which are associated with other health issues.
No deafness, eye problems or secondary joint problems have been observed in dogs affected with SD2.
Therefore, as the dogs have no health problems we are really looking at a condition that only affects their appearance and is not a disease in itself.
- Normal: The dog carries two normal copies of the gene and has no or reduced likelihood of developing SD2 during its life.
- Carrier: The dog has a normal appearance, but carries one copy of the mutation and one copy of the normal gene in its genome. A carrier transfers the disease mutation to approximately 50% of its offspring.
- Affected: The dog carries two copies of the mutation and is at high risk of developing SD2. An affected animal will pass on the mutation to all of its offspring.
All the offspring of an affected dog and a normal dog will be carriers. All offspring of two affected dogs will also be affected.
What SD2 affected means for your Labrador:
Your Labradors size and body proportions are controlled by multiple genes, not just the SD2 gene, and there will be a natural degree of size variance in the normal Labrador population.
The Kennel Clubs breed standards are:
Male Labrador Retriever: Height at withers. Ideal 56 - 57 cm. Acceptable 57- 62 cm
Female Labrador Retriever: Height at withers. Ideal 55 - 56 cm. Acceptable 55 - 60 cm
The only effect this will have is that your Labradors shorter legs will put her below the Kennel Clubs breed standard minimum height, but on a dog that otherwise might have had relatively long legs, your dog will have almost normal proportions.
Indeed many a stocky working Labrador may be SD2 affected without the owner ever realising that the slight shortness is due to the mutated gene
This has come about as over the years the simple process of mating a Labrador with shorter legs to a Labrador who is much taller than average would have helped to override the visual effect of the SD2 gene.
It has also become clear from feedback from potential owners that there is a desire for smaller shorter Labrador.
Labradors may be the worlds best loved dog, but they are large and many people want a smaller dog with the same traits.
However deliberate breeding of SD2 affected dogs to produce shorter Labradors would eventually result in extreme leg shortness, which while allowing the dog to live a normal and content life as a pet would prevent her from field work or the active sports Labradors are so fond of.
What do I do if I have a dog or bitch DNA tested as a carrier or affected with SD2?.
If all other health tests ( Hip Dysplasia, Elbow Dysplasia PRA etc...) indicate your dog is suitable for breeding. Choose a mate who is SD2 DNA tested clear.
Test the puppies in the litter at 4 weeks and advise potential owners to breed clear or carrier puppies with SD2 clear Labradors.
Reporting of SD2 gene.
Since Autumn 2014 the Kennel Club have agreed to a voluntary recording of SD2 which will appear on their mate select site and on documentation.
Owners who have had their Labradors DNA tested for the condition can send copies of their certificates to the health department as laboratories do not automatically send on certificates.
On other sites where dogs are offered for breeding, such as Champdogs.com, breeders have the opportunity to indicate if their proffered dog is SD2 clear.
US national Library of medicine Mirjam Frischknecht : Mutation in Labrador Retrievers with Mild Disproportionate Dwarfism