Skeletal Dysplasia 2 (SD2) in Labrador Retrievers

Quick Summary

Skeletal dysplasia 2 (SD2) is an inherited disorder that causes a mild form of disproportionate dwarfism consisting of short legs with normal body length and width.

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Phenotype: Skeletal dysplasia 2 (SD2) is an inherited disorder that causes a mild form of disproportionate dwarfism consisting of short legs with normal body length and width. The leg bones of affected dogs are shorter, thicker, and slightly curved; in most cases, the front legs are slightly more affected than the hind legs. The height of affected dogs is variable, and there is an overlap in shoulder height between small non-affected individuals and tall affected individuals. The SD2 mutation shows incomplete penetrance: not all dogs with two copies of the defective gene will show obvious physical characteristics of SD2.

Mode of Inheritance: Autosomal recessive (incomplete penetrance)

Alleles: N = Normal, SD2 = Skeletal dysplasia 2

Breeds appropriate for testing: Labrador Retriever, Labradoodle

Explanation of Results:

  • Dogs with N/N genotype will not have skeletal dysplasia 2 and cannot transmit this SD2 variant to their offspring.
  • Dogs with N/SD2 genotype will not be affected by skeletal dysplasia 2, but are carriers. They may transmit this SD2 variant to 50% of their offspring. Matings between two carriers are predicted to produce 25% skeletal dysplasia 2-affected puppies.
  • Dogs with SD2/SD2 genotype may develop skeletal dysplasia 2, and will transmit this SD2 variant to all of their offspring.

Results of this test can be submitted to the OFA (Orthopedic Foundation for Animals)

Turnaround Time
At least 15 business days; may be delayed beyond 15 business days if sample requires additional testing, or a new sample is requested.

$55 single test per animal ($5 discount on 3 or more dogs)
$25 as additional health test on same animal

Sample Collection

Dog DNA tests are carried out using cells brushed from your dog's cheeks and gums. The preferred cytology brushes are sent to you by mail, or you may provide your own brushes. For accepted alternative brushes, click here

We recommend waiting until puppies are at least three weeks old before testing.


Dog having its cheeks and gums brushed for DNA samples
Cheek and gum brushing technique for canine DNA sample collection


  1. Make sure the dog has not had anything to eat or drink for at least 1 hour prior to collecting sample.
  2. When swabbing puppies, isolate each puppy from the mother, littermates and any shared toys for 1 hour prior to swabbing. Puppies should not have nursed or eaten for 1 hour prior to collecting sample.
  3. If collecting samples from more than one dog, make sure to sample one dog at a time and wash your hands before swabbing another dog.
  4. Label brush sleeve with name or ID of dog to be sampled.
  5. Open brush sleeve by arrow and remove one brush by its handle.
  6. Place bristle head between the dog’s gums and cheek and press lightly on the outside of the cheek while rubbing or rotating the brush back and forth for 15 seconds.
  7. Wave the brush in the air for 20 seconds to air dry.
  8. Insert brush back into sleeve.
  9. Repeat steps 5 - 8 for each unused brush in sleeve on a fresh area of cheek and gums. Make sure to use and return all brushes sent by the VGL. In most cases, it will be 3 brushes per dog. If using interdental gum brushes, please note that the VGL requires 4 brushes per dog and only moderate or wide interdental gum brushes are accepted.
  10. Do not seal brushes in sleeve.
  11. Place all samples in an envelope and return to the address provided.


  • Do not collect saliva/drool – the key to obtaining a good sample is getting cheek cells on the swab
  • Do not rub swab on the dog’s tongue or teeth – this will result in poor quality sample
  • Do not collect a sample from a puppy that has recently nursed – the mother’s genetic material can rub off on the puppy’s mouth and contaminate the sample
Additional Details

Skeletal dysplasia 2 (SD2) is an inherited musculoskeletal disorder that causes a form of mild disproportionate dwarfism in affected dogs – their body length and width are normal, but their legs are shorter than normal. Radiological findings typically include shortened and sometimes slightly curved long bones with relatively wide epiphyses (rounded ends of long bones). The front legs are affected more frequently than hind legs. The disorder shows a subtle phenotype in which the height of affected dogs may overlap with that of small normal dogs; no ocular, auditory or secondary joint symptoms are associated with SD2. This disorder has been reported to occur more frequently in the “working” line of Labrador Retrievers, and less frequently in the “show” line.

SD2 in Labrador Retrievers is caused by a single nucleotide mutation (c.143G>C) on the collagen alpha-2(XI) chain (COL11A2) gene. The mode of inheritance for this disease is autosomal recessive, which means that males and females are equally affected and that two copies of the mutation are needed to cause the defect. Moreover, this mutation shows incomplete penetrance, and therefore not all affected dogs will show obvious physical characteristics of SD2. Screening of a random set of Labradors Retrievers at the VGL determined that the SD2 disease allele is rare in this breed, with frequency less than 1%.

Testing for SD2 can assist clinicians, owners, and breeders in identifying affected and carrier dogs. Breeders can use results from the test as a tool for selection of mating pairs to avoid producing affected dogs. Of special note is that, because of the incomplete penetrance, not all affected dogs with show obvious signs of SD2, thus making genetic testing for this disorder important to detect dogs carrying the mutation.