Molecular Analysis of Giant Schnauzer-Type Congenital Hypothyroidism

Isolated congenital hypothyroidism (CH) is a condition occurring at or near birth characterized by insufficient thyroid hormone production. The disorder in purebred dogs is usually inherited and leads to dwarfism and mental dullness.

CH in giant schnauzers (GS) was first described in 1991 (Greco, et al) as a likely autosomal recessive disorder due to failed activity of the hypothalamus or pituitary gland. Since then the investigators have studied GS CH in three widely separated families and found pituitary failure of thyroid stimulating hormone (TSH) production beginning at birth in most affected dogs, but not until several months of age in a few. They mapped the genetic locus to a region of dog chromosome 28.

The researchers will now perform DNA sequencing experiments of affected dogs and their parents and candidate variants will be assessed further by Sanger sequencing in all available members of the three families, as well as a large number of GS DNA samples available in the OFA CHIC repository. A successful outcome will lead to a reliable genetic test for GS CH, increased understanding of an essential pituitary function, and illumination of a highly similar condition reported in miniature schnauzers.

Co-sponsored with the AKC Canine Health Foundation, Grant Number: 02342

RESEARCHERS

John C Fyfe, DVM PhD
Michigan State University
Amount: $2,000

Recombinant Thyrotropin (TSH)

Standard for the Next Generation of Canine TSH Immunoassays With Improved Sensitivity

Overall, this research project completed the genetic phase of the project and are reproducibly producing reasonable quantities of recombinant canine TSH in vitro and purifying it with high recovery to high purity. In the future, this standard can serve as a reproducible standard for all available canine TSH assays. Although the researchers did not succeed with the development of a permanent cell line expression canine TSH, the transient expressions in PEAK cells and purification procedures have resulted in hundreds of micrograms of pure canine TSH devoid of contaminating LH and FSH. The data support the importance of the lack of standard cross-contamination with these more abundant but structurally related pituitary glyoprotein hormones. The research also pursued the promising development of antibody titers against TSH in 2 immunized mice. Unfortunately, neither of the animals resulted in a successful result: the positive hybridomas from one mouse were contaminated in the UGA monoclonal antibody facility, and the positive clones from the other mouse did not result in permanently positive clones.

Results

In summary, using the currently available pairing of the 14H9 monoclonal antibody with a limited quantity of anti-cTSH polyclonal antibody, the researchers have developed a canine TSH immunoassay with an IRMA format, but the assay in this format does not appear to be more sensitive than the current commercial canine TSH assay. However, the use of highly purified recombinant canine TSH does provide an improvement over the use of pituitary source TSH inevitably contaminated by LH and FSH. Such contamination provided by pituitary source glycohormones could theoretically be more problematic for accurate measurement of TSH in the cycling bitch.

Co-sponsored with the AKC Canine Health Foundation, Grant Number: 0002434

RESEARCHERS

Duncan Ferguson, DVM, PhD
University of Georgia