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Congenital Hypothyroidism with Goiter (CHG)
| Acronym: | CHG |
| Gene: | TPO |
| Mutation: | c.331C>T |
| Inheritance: | Autosomal recessive |
| Sample type: | CHS (Cheek Swab), WBE (Whole Blood EDTA) |
Genetics and characteristics
Thyroid hormone is essential for normal development and metabolism in dogs, especially in the rapid growth period that puppies experience. Congenital hypothyroidism with goiter is an inherited defect of Toy Fox Terriers and Rat Terriers caused by a mutation in the thyroid peroxidase gene. Puppies with CHG show signs of disproportionate dwarfism, abnormal hair coat, lethargy, abnormal mentation, and neurological impairment. They exhibit stenotic ear canals and delayed opening of the eye, and cervical swellings evident by 1 week of age. The disease causes improper production of an enzyme that is important in thyroid hormone production. Serum thyroid hormone and thyroid-stimulating hormone concentrations are low and high, respectively. Unless oral thyroid hormone replacement therapy is instituted early in life, the disorder is severely debilitating or lethal. Puppies exhibit avid iodide uptake and normal hearing, but the failure of iodide organification may lead to goiter.
Results Reported As
Test Result |
Interpretation of test result |
CLEAR |
Tested mutation was not detected in animal with „clear“ result. Animal tested as clear has wild-type allele in homozygous state (i.e. two pairs of healthy alleles). It will not develop disease caused by tested mutation.* It will pass only wild-type allele to its offspring. |
CARRIER |
Tested mutation was detected in animal with „carrier“ result. Animal tested as carrier has one wild-type and one mutation allele, it is in heterozygous state. It will not develop disease caused by tested mutation.* It can pass wild-type or mutation allele to its offspring. |
AFFECTED |
Tested mutation was detected in animal with „affected“ result. Animal tested as affected has two copies of mutation alleles affecting the gene. It is likely the animal will experience a genetic disorder due to this mutation.** It will pass only mutation allele to its offspring. |
*Test excludes only tested mutation but not possible unknown mutations or factors that can lead to similar condition/symptoms.
** Potential unknown mutations or multiple other factors can possibly affect the likelihood of experiencing a genetic disorder.
References:
John C Fyfe, K.K. (2003). Congenital hypothyroidism with goiter in toy fox terriers. Journal of Veterinary Internal Medicine / American College of Veterinary Internal Medicine 17, 50–57.
Pettigrew, R., Fyfe, J.C., Gregory, B.L., Lipsitz, D., Delahunta, A., Summers, B.A., and Shelton, G.D. (2007). CNS hypomyelination in Rat Terrier dogs with congenital goiter and a mutation in the thyroid peroxidase gene. Vet. Pathol. 44, 50–56.