Toy Fox Terrier — Congenital hypothyroidism with goiter (hereditary; OMIA-verified breed predisposition)

--- license: permission_granted topic_id: companion_breed_health_toy_fox_terrier_congenital_hypothyroidism_with_goiter_dog category: companion-breed-health title: "Toy Fox Terrier — Congenital hypothyroidism with goiter (hereditary; OMIA-verified breed predisposition)" lang: en source: "OMIA (Online Mendelian Inheritance in Animals, University of Sydney) breed-specific hereditary-disorder record, saved verbatim to source_file; C1 substring-verified. Pulled 2026-08-02 from local OMIA database dump." source_file: pdf-raw/breed-health/toy_fox_terrier_congenital_hypothyroidism_with_goiter_904.txt date_parsed: 2026-08-02 tokens_estimated: 1058 verification: method: substring_match claims: 10 passed: 10 date: 2026-08-02 recovered: false path: companion-breed-health/companion_breed_health_toy_fox_terrier_congenital_hypothyroidism_with_goiter_dog/01_companion_breed_health_toy_fox_terrier_congenital_hypothyroidism_with_goiter_dog.md source_document: "OMIA — Online Mendelian Inheritance in Animals (University of Sydney)" citation: authority: "OMIA — Online Mendelian Inheritance in Animals (University of Sydney)" title: "Toy Fox Terrier — Congenital hypothyroidism with goiter (hereditary; OMIA-verified breed predisposition)" url: "https://omia.org/OMIA000536/9615/" retrieved: "2026-08-02" ref: "OMIA breed-specific hereditary-disorder records (omia.org), derived from local OMIA database dump; dataset: https://doi.org/10.25910/2AMR-PV70" doc_type: "academic animal-genetics database (breed-specific disorder entries)" needs_review: false

Toy Fox Terrier — Congenital hypothyroidism with goiter (hereditary; OMIA-verified breed predisposition)

Source: first-hand OMIA (University of Sydney) breed-specific hereditary-disorder record, saved verbatim to source_file; every claim below is a C1 byte-substring of it.

Claims

• Breed: Toy Fox Terrier (Dog)
• Disorder: Congenital hypothyroidism with goiter
• Mode of inheritance: Autosomal recessive
• Summary: Congenital hypothyroidism (CH) is an endocrine disorder characterized by inadequate T4 levels early in life concurrent with signs of hypothyroidism. Disease can be primary (failure to make T4), which is due to abnormal thyroid development or function. Primary hypothyroidism often presents with goiter but can be due to thyroid dysgenesis. CH can be secondary (failure to make bioactive TSH), which is caused by abnormal pituitary development or function. CH can also be tertiary (failure to make TRH) due to abnormal hypothalamic function. Signs of CH with goiter include growth retardation (dwarfism), epiphyseal dysplasia in the vertebrae and limbs, and delay in maturation changes such as dental eruption, opening of eyes and ear canals, and growth of guard hairs. Other signs include thickened subcutis, lethargy, unresponsiveness, and failure to suckle. The disorder is lethal unless diagnosed and treated early. Goiter, extremely low T4, and increased TSH are signs in Toy Fox Terriers, Rat Terriers, Tenterfield Terriers, and Spanish Water Dogs. In dogs likely causal variants have been described in at least two genes (TPO - described in this entry, and SLC5A5 - see 'OMIA002174-9615 Hypothyroidism, congenital dyshormonogenic, with goiter). Non-genetic forms of the condition are possible and may represent some of the case studies for which references are listed in this entry. The mode of inheritance is autosomal recessive for TPO-related congenital hypothyroidism in dogs. Causative mutations in 3 terrier breeds and the Spanish water dog are all in the gene that codes for thyroid peroxidase (TPO), the enzyme responsible for irreversible binding of iodide to thyroglobulin. This process is known as organification of iodide, and it is a necessary step of thyroid hormone synthesis. If thyroid peroxidase activity is not present, the animal is unable to make T4 and presents with primary hypothyroidism. Goiter develops as thyroid cells undergo hypertrophy and hyperplasia due to unrelenting TSH stimulation. DNA-based tests are available to detect the TPO mutation in all 4 breeds. Breeding of carrier animals to each other is not recommended. If a carrier animal is bred to a homozygous normal animal, testing the offspring is advised. Edited by John C. Fyfe, D.V.M., Ph.D. (edited by IT 22/5/2022)
• Clin feat: Signs include growth retardation (dwarfism), epiphyseal dysplasia in the vertebrae and limbs, delayed dental eruption, delayed opening of eyes and ear canals, delayed haircoat maturation, thickened subcutis, lethargy, unresponsiveness, failure to suckle. Goiter, extremely low T4, and increased TSH are signs in Toy Fox Terriers, Rat Terriers, Tenterfield Terriers, and Spanish Water Dogs. Onset of signs is early (less than one week of age) in primary congenital hypothyroidism Clinical signs of iodine toxicosis in fetal and early postnatal life are similar to those of congenital hypothyroidism but the two disorders are distinguished by different thyroid histology.
• Defect: yes
• Pathology: Congenital hypothyroidism caused by a mutation in TPO is a form of dyshormonogenesis. Thyroid peroxidase is the enzyme responsible for irreversible binding of iodide to thyroglobulin, a necessary step of thyroid hormone synthesis. If thyroid peroxidase activity is not present, the animal is unable to make thyroid hormones and will present with primary hypothyroidism (Fyfe et al., 2003). Goiter will develop in a few weeks due to unrelenting TSH secretion.
• Prevalence: Most hypothyroidism is not congenital – only 3.6% of hypothyroid dogs are less than one year of age (Bojanic et al., 2011). Rat Terriers are thought to have acquired the mutation fairly recently, as a result of interbreeding with Toy Fox Terriers (Pettigrew et al., 2007).
• Control: Breeding of carrier animals to each other is not recommended. If a carrier animal is bred to a homozygous normal animal, testing the offspring is advised.
• Gen test: DNA-based tests are available to detect the mutations in all 4 breeds.

Associated gene(s)

Derived from OMIA database dump (omia.xml, local); structured field, not verbatim prose. First-hand values below are verbatim substrings of the topic's pdf-raw/omia/<phene_id>.txt source file.

• Gene: Entrez Gene ID 403521 (no symbol in OMIA GeneSynonym) — OMIA Phene_Gene

Evidence (references)

Derived from OMIA database dump (omia.xml, local); structured field, not verbatim prose. First-hand values below are verbatim substrings of the topic's pdf-raw/omia/<phene_id>.txt source file.

• 1990. Cutaneous Mucinous Vesiculation in a Dog with Hypothyroidism. Journal of the American Veterinary Medical Association — PubMed:PMID2307615 — OMIA Phene_Article / Article
• 1989. Canine Hypothyroidism - Etiology, Incidence, Symptoms, Diagnosis and Treatment. Annales de Medecine Veterinaire — OMIA Phene_Article / Article
• 1991. Congenital hypothyroid dwarfism in a family of Giant Schnauzers. J Vet Intern Med — PubMed:PMID2061865 | DOI:10.1111/j.1939-1676.1991.tb00932.x — OMIA Phene_Article / Article
• 1993. Insulin Resistance in 3 Dogs with Hypothyroidism and Diabetes mellitus. Journal of the American Veterinary Medical Association — PubMed:PMID8496104 — OMIA Phene_Article / Article
• 1993. Congenital Hypothyroidism in a Boxer Dog. Journal of Small Animal Practice — OMIA Phene_Article / Article
• 1993. Plasma Cholesterol and Lipoprotein Concentrations in the Dog - The Effects of Age, Breed, Gender and Endocrine Disease. Journal of Small Animal Practice — OMIA Phene_Article / Article
• 1993. Altered platelet indices in dogs with hypothyroidism and cats with hyperthyroidism. Am J Vet Res — PubMed:PMID8116929 — OMIA Phene_Article / Article
• 1994. Hypothyroidism in Dogs - 66 Cases (1987-1992). Journal of the American Veterinary Medical Association — PubMed:PMID8175472 — OMIA Phene_Article / Article
• 1994. Neurological Signs Related to Hypothyroidism in the Dog - Review of the Literature and Case Reports. Schweizer Archiv Fur Tierheilkunde — PubMed:PMID8091179 — OMIA Phene_Article / Article
• 1994. Plasma von Willebrand factor antigen concentration in dogs with hypothyroidism. Journal of the American Veterinary Medical Association — PubMed:PMID7730121 — OMIA Phene_Article / Article
• 1995. Isolation of thyroid peroxidase and lack of autoantibodies to the enzyme in dogs with autoimmune thyroid disease. American Journal of Veterinary Research — PubMed:PMID7695146 — OMIA Phene_Article / Article
• 1995. Hypothyroidism and von Willebrand factor. Journal of the American Veterinary Medical Association — PubMed:PMID7744675 — OMIA Phene_Article / Article
• (97 additional references in OMIA)

Comparative medicine (human OMIM)

Derived from OMIA database dump (omia.xml, local); structured field, not verbatim prose. First-hand values below are verbatim substrings of the topic's pdf-raw/omia/<phene_id>.txt source file.

• OMIM:274500 (type: trait) — OMIA Group_OMIM (via OMIA_ID)
• OMIM:606765 (type: gene) — OMIA Group_OMIM (via OMIA_ID)

verification_derived: method: derived_from_dataset source: "OMIA database dump (omia.xml, local); fields Gene/Variant/Article/OMIM" note: "Structured fields (gene, variant rsID/protein change, PubMed/DOI references, OMIM cross-link) extracted from OMIA dump and presented with first-hand values; not verbatim prose."