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Canine Genetics by & for Top Breeders

 

CANINE GENETICS

 

Dogs are one of the few species that are 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

 

CHG is a fatal hereditary defect caused by a mutation in thyroid peroxidase gene.  It has been diagnosed in French Bulldogs, Rat Terriers, Toy Fox Terriers, Tenterfield Terriers, Spanish Water Dog, some other breeds as well as cats and other domestic species. (see part 3)  Affected puppies die in the nest but CHG littermates may carry the recessive gene. If there is any unexplained occurrence of fetal death, sire and dam should be tested to avoid further corrupting the gene bank.

 

How does CHG happen? What kind of thyroid problem could affect new born animals? Is it always deadly?  These and many questions come to mind when dog breeders hear about this (thankfully) rare type of goiter. The animal breeder's bible has always been the fat brown book, the Merk Manual {1}, 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."

 

Testing for Congenital Hypothyroidism with Goiter was costly at the time this was first written (2014) because it was a new and rare genetic disease. Note that a dog is either a carrier or clear.  "Affected" can only mean it died... In 2019 a breeder notified TheDogPlace.org of a CHG case in a Toy Fox Terrier litter so the risk is still there and we felt it would be helpful to re-run this article.

 

We ask dog breeders to contact editor to report a confirmed occurrence of GHG in any breed for our privacy protected veterinary database.

 

Following a seminar on CHG at the 2014 Toy Fox Terrier National Specialty TheDogPlace.org was afforded opportunity to conduct an in-depth 3-part interview with Dr. Fyfe. See links below.

 

Easily Recognized Early Symptoms Of CHG

A puppy with CHG may be less active than his littermates. There should also be 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 before dying. In one 2019 case, the goiter restricted the  airway but mercifully it was immediately euthanized.

 

Prior to running the interview with Dr. Fyfe we contacted a group of long time TFT breeders and asked if they, or anyone they knew, had produced a litter containing congenital hypothyroidism with goiter (CHG).  Although some responses were defensive, most were cooperative, intrigued, and willing to discuss and report suspected incidents but no cases of CHG were confirmed at that time.

 

We have been unable to verify the bloodline (or existence of) the CHG-afflicted Toy Fox Terriers in New Zealand as referenced by Dr. Fyfe in the 2014 interview. The TFT was AKC recognized (registered) in 2003 but UKC began registering the breed in 1936 so the dogs he referenced may have been old or mixed bloodlines.

 

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

 

Is it too early to provide numbers on the accuracy of the test?

Does DNA testing indicate whether Congenital Hypothyroidism with Goiter is hereditary or acquired? Where does a university obtain funding for such a rare problem in a rare breed?

Is the disorder present in other breeds and if so, is research being conducted for them?

Are there numerical statistics on how many dogs are affected? Why is New Zealand mentioned?

ref 1 Merk Manual Professional

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 3 - CHG-4 Testing Cost, by Dr. Fyfe

 

Copyright TheDogPlace.org #124173r1901 http://www.thedogplace.org/GENETICS/CHG-1-Intro-to-Congenital-Hypothyroidism-With-Goiter-b19A01.asp

 

 

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