Congenital Hypothyroidism with Goiter in Dogs: Causes & Care

The Spanish Water Dog and several other breeds can be affected by congenital hypothyroidism with goiter (CHG), a serious inherited disorder impacting thyroid hormone production. If untreated, CHG often proves fatal in puppies, but early diagnosis and management can improve outcomes. Responsible breeders routinely perform genetic carrier testing to help reduce the risk of spreading this condition.

Understanding Congenital Hypothyroidism with Goiter

The thyroid hormone is critical for normal growth and metabolism, especially in puppies undergoing rapid development. In puppies affected by CHG, thyroid hormone deficiency results in delayed physical and neurological growth. These puppies often have unusually large heads, delayed opening of eyes and ear canals, and show reduced activity compared to littermates.

A hallmark sign is the development of a swelling under the neck—known as a goiter—which can sometimes be misdiagnosed as an infection like strangles. Distinctive features also include dwarfism due to shortened bones, abnormal coat texture, and difficulties in breathing caused by goiter pressing on the airways.

The Genetic Cause and Inheritance

CHG is caused by mutations primarily affecting the thyroid peroxidase (TPO) gene, essential for thyroid hormone synthesis. It follows an autosomal recessive inheritance pattern, meaning a puppy must inherit two copies of the mutated gene, one from each parent, to be affected.

• If both parent dogs are carriers, there is around a 50% chance their puppies will also be carriers and a 25% chance a puppy will be affected.
• Parents may appear healthy but can pass the defective gene to offspring unknowingly.

Without testing, carriers may breed continuously, propagating the disorder within the breed population. Therefore, identifying carriers through DNA testing is an essential step in responsible breeding.

Recognising the Signs and Symptoms

Signs usually become evident within the first few weeks of life and include:

• Delayed growth and diminished activity
• Disproportionately large head and dwarfism
• Persistent eye and ear canal closure beyond normal age
• Wiry or abnormal coat texture
• Neck swelling (goiter) which can obstruct breathing
• In some cases, mental dullness and poor nursing behaviours

Early veterinary consultation is crucial if these symptoms are observed to confirm diagnosis and begin treatment.

Diagnosis and DNA Carrier Testing

Diagnosis involves a combination of clinical observation, blood tests assessing thyroid hormone levels, and molecular genetic testing. The DNA test detects the mutated TPO gene from blood samples, cheek swabs, or semen. This genetic screening is vital in identifying carrier dogs, allowing breeders to make informed mating decisions and avoid producing affected puppies.

Testing is widely available via veterinary diagnostic laboratories specialising in genetics. For instance, samples can be submitted to laboratories like Laboklin or Michigan State University's Laboratory of Comparative Medical Genetics.

Managing and Treating CHG

While congenital hypothyroidism with goiter is serious, early and continuous treatment with synthetic thyroid hormone replacement can alleviate many symptoms and improve quality of life. Careful monitoring by a veterinary professional is required to manage hormone doses and watch for complications such as airway obstruction due to enlarged thyroid tissue.

Despite treatment, some physical deformities may persist, and affected dogs require lifelong support and medication.

Preventing CHG Through Responsible Breeding

The most effective strategy to reduce CHG is genetic testing of breeding dogs to avoid mating carriers together. This reduces the risk of affected puppies and limits the transmission of the mutation throughout the breed population. Prospective dog owners are encouraged to find a puppy from reputable breeders who prioritise health testing and ethical breeding practices.

Responsible ownership means being informed about potential hereditary conditions and supporting responsible breeders who test for CHG and other genetic disorders.

Conclusion

Congenital hypothyroidism with goiter is a serious inherited thyroid disorder affecting the Spanish Water Dog and other breeds. Early recognition, diagnosis, and lifelong treatment can significantly improve affected dogs’ quality of life. Most importantly, widespread DNA carrier testing and responsible breeding are key to preventing this tragic condition from continuing to affect new generations.