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Congenital Hypothyroidism with Goiter (CHG) – Spanish Water Dog Type
| Acronym: | CHG |
| Gene: | TPO |
| Mutation: | c.39_40insG |
| Inheritance: | Autosomal Recessive |
| Sample type: | CHS (Cheek Swab), WBE (Whole Blood EDTA) |
Genetics and characteristics
Congenital Hypothyroidism With Goiter (CHG) is a genetic endocrine disorder typically due to a defect of thyroid hormone synthesis causing a lack of thyroid hormones in the bloodstream. Thyroid disorders are common diseases that affect humans and various types of animals, including dogs, and may be caused by a late fetal or neonatal iodine excess or may have a genetic cause. The type of hypothyroidism found in Spanish Water dogs is often accompanied by a swelling in the neck resulting from an enlarged thyroid gland (goiter) and is caused by a mutation within the thyroid peroxidase gene (TPO). TPO is a multifunctional enzyme whose activity is required for normal thyroid gland function. Affected dogs often show a delay in growth, disproportionate dwarfism due to bone malformations, abnormal hair texture, lethargy, and severe mental retardation.
This type of congenital hypothyroidism specific to Spanish Water dogs is inherited as an autosomal recessive trait, requiring two copies of the mutated gene for the disease to develop. Dogs with only one copy of the mutated gene will not develop the disease but may act as carriers and pass the mutation to their offspring. Early detection by genetic testing can identify carriers and help breeders in selecting future mating pairs which can be used to avoid unintentional breeding of affected dogs.
Results Reported As
Test Result |
Interpretation of test result |
CLEAR |
Tested mutation was not detected in animal with „clear“ result. Animal tested as clear has wild-type allele in homozygous state (i.e. two pairs of healthy alleles). It will not develop disease caused by tested mutation.* It will pass only wild-type allele to its offspring. |
CARRIER |
Tested mutation was detected in animal with „carrier“ result. Animal tested as carrier has one wild-type and one mutation allele, it is in heterozygous state. It will not develop disease caused by tested mutation.* It can pass wild-type or mutation allele to its offspring. |
AFFECTED |
Tested mutation was detected in animal with „affected“ result. Animal tested as affected has two copies of mutation alleles affecting the gene. It is likely the animal will experience a genetic disorder due to this mutation.** It will pass only mutation allele to its offspring. |
*Test excludes only tested mutation but not possible unknown mutations or factors that can lead to similar condition/symptoms.
** Potential unknown mutations or multiple other factors can possibly affect the likelihood of experiencing a genetic disorder.
References:
Fyfe, J.C., Lynch, M., Olsen, J. et al. A thyroid peroxidase (TPO) mutation in dogs reveals a canid-specific gene structure. Mamm Genome 24, 127–133 (2013). https://doi.org/10.1007/s00335-012-9442-y
Kopke, M.A., Mukorera, V., Leisewitz, A.L. and Ruaux, C.G. (2019), Chronic lameness associated with congenital hypothyroidism in three dogs. Vet Rec Case Rep, 7: e000916. https://doi.org/10.1136/vetreccr-2019-000916