Genetic basis of Congenital Hypothyroidism with Goiter - in Tenterfield Terriers is an autosomal recessive inherited metabolic disorder caused by a mutation affecting a key enzyme involved in thyroid hormone production, most commonly thyroid peroxidase (TPO). This enzyme deficiency impairs normal synthesis of thyroid hormones, which are essential for metabolism, growth, and development. Dogs must inherit two copies of the pathogenic mutation (one from each parent) to be clinically affected. Carriers carry one copy without clinical signs but can pass the mutation to offspring. Genetic testing for this mutation is available and important for breeding programs to prevent affected puppies.
Pathophysiology - Thyroid hormone is critical for normal development, metabolism, and neurological function. Deficiency leads to widespread effects in growing puppies. The enzyme deficiency prevents adequate production of thyroid hormones, resulting in hormone deficiency despite an enlarged thyroid gland (goiter), which forms as the gland attempts unsuccessfully to compensate by growing larger. Affected puppies show signs by 3 to 8 weeks of age, including: Reduced spontaneous movement and activity. Failure to grow normally (dwarfism) with short limbs. Large head relative to body size. Fluffy, woolly hair coats that lack normal guard hairs. Delayed opening of the eyes and ear canals. Neurological and neuromuscular deficits due to inadequate hormone supply during critical developmental periods. If uncorrected, the condition causes failure to thrive and progressive neurological impairment.
Complications - Goiter enlargement may continue despite thyroid hormone treatment and may grow large enough to compress the airway, causing breathing difficulties. Affected dogs may show severe dwarfism and permanent neurological deficits if treatment is delayed or absent. Without early diagnosis and thyroid hormone supplementation, puppies fail to thrive and often die prematurely. Early intervention with hormone replacement prevents most clinical signs from progressing and can reverse many symptoms, but the goiter itself may persist or enlarge.
Why This Matters to Breeders and Vets
Breeders: Because CHG is autosomal recessive, DNA screening is essential to identify carriers and affected dogs to avoid producing puppies with this severe and potentially fatal disorder. Responsible breeding reduces disease incidence while preserving genetic diversity in the breed.
Veterinarians: Early recognition of clinical signs in young puppies combined with genetic testing facilitates prompt diagnosis. Early thyroid hormone therapy is critical to prevent irreversible developmental defects and improve survival. Vets should monitor goiter progression as it may affect airway function despite treatment.
Management: Lifelong thyroid hormone supplementation is required for affected dogs. Supportive care may be needed to manage neurological and growth-related effects, especially if treatment begins late.
Summary - Congenital Hypothyroidism with Goiter in Tenterfield Terriers is a genetically inherited autosomal recessive disorder caused by enzyme deficiency critical for thyroid hormone production. It manifests early in life (3–8 weeks) with dwarfism, neurological deficits, and characteristic goiter formation. Early diagnosis and lifelong thyroid hormone replacement therapy can prevent or reverse many symptoms, but goiter size may still enlarge and complicate breathing. Genetic testing enables breeders to identify carriers and affected dogs, supporting responsible breeding to reduce disease prevalence and improve puppy health outcomes.