Juvenile onset
For autosomal recessive disorders, dogs with two copies of the variant are at risk of developing the condition. Dogs with one copy of the variant are considered carriers and are usually not at risk of developing the disorder. However, carriers of some complex variants grouped in this category may be associated with a low risk of developing the disorder. Individuals with one or two copies may pass the disorder-associated variant to their puppies if bred.
At risk dogs are likely to show signs of this disease in their lifetime.
Partner with your veterinarian to make a plan regarding your dog’s well-being, including any insights provided through genetic testing. If your pet is at risk or is showing signs of this disorder, then the first step is to speak with your veterinarian.
Affected puppies appear normal at birth, with slowed growth usually observed around 3 to 8 weeks of age. Disproportionate dwarfism is typical for affected puppies: they have wide heads, short and thick necks, and short limbs. Affected puppies show mental impairment and their puppy coats are not replaced with the adult coat. Delayed opening of eyes and ear canals and delayed teething may be observed. Goiter (swelling and enlargement of the thyroid gland) is also observed. The disease may lead to death during the first weeks of life due to failure to thrive.
Most clinical signs will improve or be prevented if the condition is recognized early and thyroid replacement therapy is instituted. However, the thyroid glands may continue to expand despite treatment which could lead to airway obstruction.
There are many responsibilities to consider when breeding dogs. Regardless of test results it is important that your dog is in good general health and that you are in a position to care for the puppies if new responsible owners are not found. For first time or novice breeders, advice can be found at most kennel club websites.
This disease is autosomal recessive meaning that two copies of the mutation are needed for disease signs to be shown. A carrier dog with one copy of the Congenital Hypothyroidism mutation can be safely bred with a clear dog with no copies of the Congenital Hypothyroidism mutation. About half of the puppies will have one copy (carriers) and half will have no copies of the Congenital Hypothyroidism mutation. Puppies in a litter which is expected to contain carriers should be tested prior to breeding. Carrier to carrier matings are not advised as the resulting litter may contain affected puppies. Please note: It is possible that disease signs similar to the ones caused by the Congenital Hypothyroidism mutation could develop due to a different genetic or clinical cause.
| Gene | TPO |
|---|---|
| Variant | C>T |
| Chromosome | 17 |
| Coordinate | 799,099 |
All coordinates reference CanFam3.1
Bojanić, K., Acke, E., & Jones, B. R. (2011). Congenital hypothyroidism of dogs and cats: A review. New Zealand Veterinary Journal, 59(3), 115–122. View the article
Fyfe, J. C., Lynch, M., Olsen, J., & Louër, E. (2013). A thyroid peroxidase (TPO) mutation in dogs reveals a canid-specific gene structure. Mammalian Genome, 24(3–4), 127–133. View the article
Fyfe, J. C., Kampschmidt, K., Dang, V., Poteet, B. A., He, Q., Lowrie, C., … Fetro, V. M. (2003). Congenital Hypothyroidism with Goiter in Toy Fox Terriers. Journal of Veterinary Internal Medicine, 17(1), 50–57. View the article
Dodgson, S. E., Day, R., & Fyfe, J. C. (2012). Congenital Hypothyroidism with Goiter in Tenterfield Terriers. Journal of Veterinary Internal Medicine. View the article
Pettigrew, R., Fyfe, J. C., Gregory, B. L., Lipsitz, D., DeLahunta, A., Summers, B. A., & Shelton, G. D. (2007). CNS hypomyelination in rat terrier dogs with congenital goiter and a mutation in the thyroid peroxidase gene. Veterinary Pathology, 44(1), 50–56. View the article
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