Congenital hypothyroidism with goiter (CHG)
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 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 eye opening, and cervical swellings evident by 1 week of age. The disease causes imporer production of enzyme that is important in the 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 failure of iodide organification which leads to goiter.
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.