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Congenital Hypothyroidism French Bulldog Type (CHG)
| Acronym: | CHG |
| Gene: | TPO |
| Mutation: | c.2242+2T>C |
| Inheritance: | Autosomal recessive |
| Sample type: | CHS (Cheek Swab), WBE (Whole Blood EDTA) |
Genetics and characteristics
Congenital Hypothyroidism French Bulldog Type (CHG) is a congenital disorder of the thyroid gland. In general, congenital goiter is an enlargement of the thyroid gland. This enlargement may cause decreased, increased, or normal thyroid hormone secretion. In hypothyroidism, the secretion of the thyroid hormone is decreased, which causes many consequential symptoms. Generally, hypothyroidism occurs most commonly in dogs but can develop also in other species, such as cats or horses. The thyroid gland is one of the most prominent endocrine glands in the dog’s body. It is responsible for controlling the metabolism in general: rate of use of energy sources, protein synthesis, and regulations regarding other hormones. These all processes are regulated by the production of thyroid hormones, which regulate the growth and rate of function of many other body systems. For proper thyroid function iodine is essential.
Usually, hypothyroidism develops in the adult age of a dog, but sometimes it can also occur in the neonatal period. As well as in humans, the early occurrence of goiter signals hypothyroidism caused by dyshormonogenesis. Congenital Hypothyroidism French Bulldog Type (CHG) causes slow physical and mental development and other symptoms collectively known as cretinism, and other metabolic abnormalities. Common symptoms shown by CHG-affected puppies are delayed opening of eyes and ear canals, poor nursing, inactivity, unresponsiveness to environmental stimuli, hypomyelination of the central nervous system, and disproportionate dwarfism caused by epiphyseal dysplasia and macroglossia. Congenital Hypothyroidism in dogs is mostly a hereditary disorder of metabolism but there can be also other causes of its occurrence, such as late fetal or neonatal iodine excess or deficiency or also consumption of a variety of drugs in the neonate or pregnant dam.
Congenital Hypothyroidism with goiter (CHG) has been identified also in several other breeds, such as toy fox, rat, and Tenterfield terriers, and in Spanish water dogs. Although the symptoms appear to be similar, in each of these breeds has been detected a breed-specific mutation in the TPO (thyroid peroxidase) gene causes CHG. Mutations in the same gene are also the most common cause of CHG in human patients. Thyroid peroxidase protein is necessary for the synthesis of thyroid hormone. When there is a lack of TPO in the organism, iodide is not able to incorporate into thyroglobulin, and consequently, failure of thyroid hormone synthesis occurs. Congenital Hypothyroidism (CHG) French Bulldog Type is inherited in an autosomal recessive pattern. Heterozygotes have no symptoms. Dogs homozygous for the mutation will display the CHG symptoms. At conception, each cub has a 25% chance of being affected, a 50% chance of being an asymptomatic carrier, and a 25% chance of being unaffected and not a carrier.
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:
Major et al. (2015.): Molecular Genetic Characterization of Thyroid Dyshormonogenesis in a French Bulldog. J Vet Intern Med 29: 1534-1540.