Test Detail

Congenital hypothyroidism with goitre in the Spanish Water Dog: a defect of thyroid hormone synthesis (dyshormonogenesis) due to absence of thyroperoxidase (TPO) activity. Affected puppies show growth retardation, sparse coat, lethargy and cold intolerance, with low thyroid hormones (T4, T3). The molecular defect is a guanosine insertion in exon 1 of TPO (poly-G tract of 8 nt, canine-specific gene structure). It is inherited in an autosomal recessive manner. The genetic test complements hormonal diagnosis; treatment is lifelong oral levothyroxine.

Affected breed: Spanish Water Dog (documented in two half-sibling puppies; Fyfe et al. 2013). Population frequency: limited data.

- Growth retardation (small skeleton)\n- Sparse, fine, dull coat\n- Severe lethargy\n- Difficulty regulating body temperature (cold intolerance)\n- Delayed neurological development\n- Muscle weakness\n- Puffy face (hypothyroid facies)\n- Bradycardia (slow heart)\n- Constipation

In 2013, Fyfe and colleagues described CHG in two half-sibling Spanish Water Dog puppies with documented absence of TPO activity and undetectable immunoreactive protein in thyroid tissue. The guanosine insertion segregated with the disease allele in the breed and was not observed in unrelated dogs of other breeds. Comparison with other mammals revealed that the poly-G tract forces an alternative translation start site, a feature specific to canids. CHG due to TPO defect has also been described in other breeds (e.g. Tenterfield Terrier, Dodgson 2012).

- Test breeding animals with the TPO insertion test before mating.\n- Do not mate two carriers: 25 %% risk of affected homozygotes.\n- A carrier can be mated with a clear animal; test the offspring intended for breeding.\n- In puppies with growth retardation, sparse coat and lethargy, request T4/T3 and confirm with a genetic test.\n- With early levothyroxine treatment the prognosis is good; record cases in the pedigree.

The diagnosis is suspected from clinical signs + low thyroid hormones (T4, T3). The genetic test confirms it.\n\nTreatment is lifelong: daily oral levothyroxine (synthetic T4). The dose is adjusted according to hormone levels and clinical response.\n\nWith adequate treatment, affected dogs can have a relatively normal life. The prognosis is good if diagnosed early and treatment is maintained.\n\nEarly detection is crucial: immediate treatment after birth significantly improves the neurological prognosis.

1. Fyfe JC et al. 2013, mutación de TPO revela estructura génica canino-específica; CHG en dos cachorros de Perro de Agua español (PMID 23223904)
2. Dodgson SE et al. 2012, hipotiroidismo congénito con bocio en Tenterfield terriers (PMID 23113744)
3. OMIA:000536 Hipotiroidismo congénito con bocio (dishormonogénesis)