CANINE GENETICS

4-part series - Dogs and humans are among the species born with this condition which may obstruct airways and prevent swallowing in which case the puppy does not survive.

CHG 1: Introduction To Canine CHG

2019 Update by Barbara J. Andrews

Congenital Hypothyroidism with Goiter is a fatal hereditary defect in these breeds wherein affected puppies die in the nest but littermates may carry the recessive gene.

In the Spring of 2019 a Toy Fox Terrier breeder notified me of a CHG case so we felt it would be helpful to re-run this informative 3-part series by John C. Fyfe, D.V.M., Ph.D. see links below.

Congenital Hypothyroidism with Goiter (CHG) is a fatal hereditary defect caused by a mutation in thyroid peroxidase gene. Congenital hypothyroidism (CH, with or without goiter) also occurs in humans, affecting about one in every 3,500 babies, with twice as many females as males affected. No sex-related studies have been done in dogs and not much as regards breeds affected by CHG.

However... the incidence of human CHG is attributed (worldwide) to a shortage of iodine in the mother's diet. Note this also explains the high incidence of thyroid disease in "northern breeds" that evolved traditionally on a diet high in seafood which contains natural iodine. This is not to suggest adding more iodine to a dog’s diet, over and above what is formulated in commercial diets, because if the dog is pregnant or lactating, the excess iodine can suppress and damage the fetus’ or puppies’ thyroid gland and cause CHG. This occurred with bad results by a miss-formulation of a canine diet in Argentina a few years ago. Unfortunately, if a little is good, more is not always better.

CHG has been diagnosed in French Bulldogs, Rat Terriers, Toy Fox Terriers, Tenterfield Terriers, Spanish Water Dogs, and some other breeds as well as cats and other domestic species. (see part 3)  Puppies affected by CHG may die in the nest so if there is any unexplained occurrence of death, sire and dam should be tested to avoid further corrupting the gene bank.

The animal breeder's bible has always been the fat brown book, The Merck Manual, which is now online. It states "Genetic defects in thyroid hormone production result in increased levels of thyroid-stimulating hormone (TSH), which in turn can cause congenital goiter. Goiter is present in about 15% of cases of congenital hypothyroidism."  Note that a dog is either a carrier or clear.  "Affected" can only mean it died... Contact Dr. Fyfe to report a confirmed occurrence of GHG in any breed.

Easily Recognized Symptoms Of CHG

A puppy with CHG may be less active than his littermates. Affected puppies fail to thrive, may be smaller, may show outward signs of dwarfism such as shorter legs than littermates but an easily recognized sign is a too-large head. You may note a difference in coat length and texture such as a "fluffy" appearance instead of flat, shiny coat in a short-coated breed. Upon confirmed diagnosis of CHG, an affected puppy should be put to sleep as there is no cure and the puppy will suffer dreadfully.

With clarity and consideration for the limitations of our layman's understanding Dr. Fyfe provided detailed information on Congenital Hypothyroidism with Goiter in the 3-part interview which follows.

For detailed information on canine CHG (Congenital Hypothyroidism with Goiter) continue to

Part 2 - About Congenital Hypothyroidism with Goiter (CHG)

Part 3 - CHG-3 Genetic Basis, by Dr. Fyfe      Part 4 - CHG-4 Testing and Cost, by Dr. Fyfe

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