Common Symptoms
Congenital hypothyroidism with goiter (Spanish water dog type) (CHG) is an inherited condition known to affect dogs. Affected dogs lack an Enzyme important for proper thyroid function and the production of thyroid hormone. Thyroid hormone is necessary for a dog’s normal development and metabolism. Around 2 weeks of age, dogs with CHG are generally noted to have reduced movement and are smaller when compared to their littermates. Enlarged thyroid glands (goiter) are often noticeable as a swelling on the neck. Affected puppies may exhibit dwarfism with short legs, large heads, and fluffy hair coats absent of guard hairs. In addition, affected dogs may develop a wide variety of neurological and neuromuscular deficits. The condition progresses to failure to thrive and death. Most symptoms can be prevented or will regress if the condition is diagnosed early and affected dogs are treated. However, the thyroid glands may continue to enlarge over time, despite treatment, and may create complications such as airway obstruction.
Testing Tips
Genetic testing of the TPO gene will reliably determine whether a dog is a genetic Carrier of congenital hypothyroidism with goiter (Spanish water dog type). Congenital hypothyroidism is inherited in an Autosomal Recessive manner in dogs. This means a dog must receive two copies of the mutated gene (one from each parent) to develop the disease. In general, carrier dogs do not have features of the disease but when bred with another carrier of the same Mutation, there is a risk of having affected pups. Each pup born to this pairing has a 25% chance of inheriting the disease and a 50% chance of inheriting one copy and being a carrier of the TPO gene mutation. Reliable genetic testing is important for determining breeding practices. To eliminate this mutation from breeding lines and avoid the potential of producing affected pups, breeding known carriers to each other is not recommended. Dogs that are not carriers of the mutation have no increased risk of having affected pups.
There may be other causes of this condition in dogs and a normal result does not exclude a different mutation in this gene or any other gene that may result in a similar genetic disease or trait.
References
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Fyfe JC, Lynch M, Olsen J, Louёr E. A thyroid peroxidase (TPO) mutation in dogs reveals a canid-specific gene structure. Mamm Genome. 2013 Apr;24(3-4):127-33. Epub 2012 Dec 8. [Pubmed: 23223904].
