Congenital hypothyroidism with goiter (CHG) is an inherited disease affecting dogs. Affected dogs lack an Enzyme that is important in the production of thyroid hormone which is necessary for the normal development and metabolism of dogs. At 3-8 weeks of age, dogs with CHG are generally noted to have reduced movement and to be small when compared to their littermates. Enlarged thyroid glands (goiter) are often noticeable as a swelling on the neck. Affected puppies exhibit dwarfism with short legs, large heads, and fluffy hair coats absent of guard hairs. In addition, affected dogs 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 with thyroid hormone medication. However, the thyroid glands may continue to enlarge over time despite treatment and can eventually obstruct the dog’s airway.
Breed-Specific Information for the Miniature Fox Terrier
Miniature fox terrier is included as a breed susceptible to congenital hypothyroidism with goiter (terrier type) because of its close relatedness to the toy fox terrier breed, which is known to develop this disease due to Mutation of the TPO gene. The frequency of the causal mutation in the general miniature fox terrier population is unknown.
Genetic testing of the TPO gene in miniature fox terrier will reliably determine whether a dog is a genetic Carrier of congenital hypothyroidism with goiter (terrier type). Congenital hypothyroidism with goiter (terrier type) is inherited in an Autosomal Recessive manner in dogs meaning that they 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 that is 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. In order to eliminate this mutation from breeding lines and to avoid the potential of producing affected pups, breeding of known carriers to each other is not recommended. Miniature fox terriers 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.
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