RESUMO
BACKGROUND: A cluster of cases of congenital hypothyroidism with goiter (CHG) in Tenterfield Terriers was identified and hypothesized to be dyshormonogenesis of genetic etiology with autosomal recessive inheritance. OBJECTIVES: To describe the phenotype, thyroid histopathology, biochemistry, mode of inheritance, and causal mutation of CHG in Tenterfield Terriers. ANIMALS: Thyroid tissue from 1 CHG-affected Tenterfield Terriers, 2 affected Toy Fox Terriers, and 7 normal control dogs. Genomic DNA from blood or buccal brushings of 114 additional Tenterfield Terriers. METHODS: Biochemical and genetic segregation analysis of functional gene candidates in a Tenterfield Terrier kindred. Thyroid peroxidase (TPO) iodide oxidation activity was measured, and TPO protein and SDS-resistant thyroglobulin aggregation were assessed on western blots. TPO cDNA was amplified from thyroid RNA and sequenced. Exons and flanking splice sites were amplified from genomic DNA and sequenced. Variant TPO allele segregation was assessed by restriction enzyme digestion of PCR products. RESULTS: Thyroid from an affected pup had lesions consistent with dyshormonogenesis. TPO activity was absent, but normal sized immunocrossreactive TPO protein was present. Affected dog cDNA and genomic sequences revealed a homozygous TPO missense mutation in exon 9 (R593W) that was heterozygous in all obligate carriers and in 31% of other clinically normal Tenterfield Terriers. CONCLUSIONS: The mutation underlying CHG in Tenterfield Terriers was identified, and a convenient carrier test made available for screening Tenterfield Terriers used for breeding.
