Hypomyelination (HYM) in Weimaraner Dogs


Researchers from the University of Wisconsin Madison lead by Dr. Ian Duncan in collaboration with researchers from Dr. Patel’s Laboratory at The University of Southern California and Dr. Bannasch’s Laboratory here at University of California Davis have identified the genetic basis for hypomyelination in the Weimaraner. The manuscript detailing this discovery is in press in the journal GLIA. 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.

Hypomyelination test information:

DNA tests for Hypomyelination can be done to assist owners and breeders in identifying affected and carrier dogs. The test uses DNA collected from buccal swabs thus avoiding blood collection. Breeders can use results from the test as a tool for selection of mating pairs to avoid producing affected dogs.

The following chart details the expected outcomes of matings for all possible combinations of Hypomyelination genotypes.


N/N100% N/N50% N/N, 50% N/HYM100% N/HYM
N/HYM50% N/N, 50% N/HYM25% N/N, 50% N/HYM, 25% HYM/HYM50% N/HYM, 50% HYM/HYM

Results reported as:

N/N: no copies of hypomyelination mutation; dog is normal
N/HYM: 1 copy of hypomyelination mutation; dog is normal but is a carrier
HYM/HYM: 2 copies of hypomyelination mutation; dog is affected.

Dogs that have only one mutant copy of HYM (N/HYM) 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 (N/HYM); however, the number of carriers can change with each generation. Dogs that are carriers of HYM (N/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.


Pemberton TJ, Choi S, Mayer JA, Li FY, Gokey N, Svaren J, Safra N, Bannasch DL, Sullivan K, Breuhaus B, Patel PI, Duncan ID. (2013) A mutation in the canine gene encoding folliculin-interacting protein 2 (FNIP2) associated with a unique disruption in spinal cord myelination. Glia 62:39-51.

Source : Weimaraner Club of America

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