Hypomyelination in Weimaraners (HYM)

Quick Summary

Hypomyelination in Weimaraners leads to tremors during puppyhood that often resolve by 3-4 months of age.

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Phenotype: Hypomyelination leads to tremors during puppyhood. Affected puppies have tremors when awake as early as 2 weeks of age. Clinical signs resolve in most cases by 3-4 months of age, though some of the dogs may have a mild persistent tremor of the hind legs.

Mode of Inheritance: Autosomal recessive

Alleles: N = Normal, HYM = Hypomyelination

Breeds appropriate for testing: Weimaraner

Explanation of Results:

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

Researchers from the University of Wisconsin, Madison, lead by Dr. Ian Duncan, in collaboration with researchers from Dr. Patel’s Laboratory at University of Southern California and Dr. Bannasch’s Laboratory at University of California, Davis have identified the genetic basis for hypomyelination (HYM) in the Weimaraner. This condition leads to tremors during puppyhood. The disease is inherited as a simple autosomal recessive disorder and the carrier frequency has been estimated to be 4.29% within the breed. Hypomyelination is also called "tremors" and "shaking puppies" by dog breeders based on the fact that affected puppies have tremors when awake as early as 2 weeks of age. Clinical signs resolve in most cases by 3-4 months of age. Some of the dogs may have a mild persistent tremor of the hind legs.

Testing for hypomyelination assists 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.

Dogs that have only one mutant copy of HYM (N/HYM genotype) are normal but they are carriers of the disease. When two carriers are bred to each other the resulting puppies can be affected. At the time that this test was released, approximately 4.3% of Weimaraners were carriers of HYM; however, the number of carriers can change with each generation. Dogs that are carriers of HYM are completely normal and they can be safely bred to dogs that are non-carriers of HYM (N/N) in order to maintain diversity within the breed and to select for other positive attributes in carrier dogs.