What is Congenital Hypothyroidism in dogs?

Both dogs and people have a small gland in their throats called the thyroid gland. One of the functions of the thyroid is to produce two hormones called thyroxine and calcitonin that regulate the body’s metabolism. When too little of these hormones are made by the thyroid, a condition called Hypothyroidism develops. This can be due to a number of reasons from cancer to injury, but an inherited defect that results in this condition is called Congenital Hypothyroidism. Congenital Hypothyroidism affects the development of the thyroid in puppies leading to an underdeveloped thyroid gland.

Genetics of Congenital Hypothyroidism

Congenital Hypothyroidism in dogs is the result of a single point mutation on the thyroid peroxidase (TPO) gene. Congenital Hypothyroidism has a autosomal recessive pattern of inheritance meaning that both parents of an affected dog have to be either carriers or affected by the condition. A Clear DNA disease screening test for this mutation in just one parent means that the whole litter will not be affected by the disease.

What is the severity of Congenital Hypothyroidism in dogs?

Congenital Hypothyroidism in dogs has a medium to high level of severity depending on when the dog is diagnosed and treated. Puppies must be identified before the age of three weeks and begin treatment immediately if they are to survive to adulthood. Dogs treated early often live a relatively normal life while others treated in the same way my have shortened lifespans.

What are the symptoms of Congenital Hypothyroidism in dogs?

Puppies with Congenital Hypothyroidism may or may not have the presence of a goiter, seen as a large lump in the throat. Puppies with Congenital Hypothyroidism will grow slower than their siblings in the same litter. They often have physical deformities such as very short legs (similar to dwarfism in dogs), large heads and a range of other deformities in other bones in their bodies. They may also have abnormal coats such as fluffier coated breeds lacking the longer guard hairs that are usually present. Another common symptom is lethargy in the puppies as their metabolism is affected by the condition. If left untreated, the damage caused by the lack of metabolism will affect every major system of the body leading to the early death of the puppy.

Diagnosis of Congenital Hypothyroidism

Before the development of a diagnostic DNA Screening test to assess dogs as either clear, carrier or affected dogs, diagnosing Congenital Hypothyroidism in time to help the puppy (by 3 weeks of age) was very difficult. The symptoms in their early stages could be missed as almost normal differences in puppy development. DNA Disease Screening will reliably determine what status the dog is (clear, carrier or affected) in relation to Congenital Hypothyroidism.

Treatment and prognosis of dogs with Congenital Hypothyroidism

Diagnosis and treatment of dogs with Congenital Hypothyroidism must begin by the time the puppy is 3 weeks of age for any hope of a successful outcome or the puppy surviving long enough to become an adult. Puppies treated early with thyroid hormone medications such as thyroxine supplements have a good chance of the condition regressing before too much damage is done, but not all cases will have the same outcome.

References

Bojanic K, Acke E, Jones BR. Congenital hypothyroidism of dogs and cats: a review. N Z Vet J. 2011 May; 59(3):115-22
Ferguson DC. Testing for hypothyroidism in dogs. Vet Clin North Am Small Anim Pract. 2007 Jul; 37(4):647-69
Fyfe JC, Kampschmidt K, Dang V, Poteet BA, He Q, Lowrie C, Graham PA, Fetro VM. (2003) Congenital hypothyroidism with goiter in toy fox terriers. J Vet Intern Med 17(1):50-7
Pettigrew R, Fyfe JC, Gregory BL, Lipsitz D, Delahunta A, Summers BA, Shelton GD. CNS hypomyelination in Rat Terrier dogs with congenital goiter and a mutation in the thyroid peroxidase gene. Vet Pathol. 2007 Jan; 44(1):50-6