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Hypothyroidism Article |
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OFA Thyroid Registry |
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Purpose
The purposes of the OFA thyroid registry are: |
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Background on Thyroid Imbalances
Autoimmune thyroiditis is the most common cause of primary hypothyroidism in dogs, causing over 50% of the cases. It is the inherited form of hypothyroidism and is thought to be polygenetic. Primary refers to those cases of hypothyroidism associated with only the thryoid gland, not the pituitary or hypothalamus. (see Table 1.)The disease has variable onset, but tends to clinically manifest itself by 2 to 5 years of age. Hence, dogs may be clinically normal for years, only to become hypothyroid at a later date. Symptoms will not appear until about 75% of the thyroid gland is already destroyed. The incidence of hypothyroidism in Samoyeds is approximately 6%. Symptoms are wide ranging, and may be confused with a lot of other disease entities. Table 2. lists symptoms which can be attributed to an inadequate level of circulating thyroxin (T4). The markers for autoimmune thyroiditis, autoantibody formation (autoantibodies to thyroglobulin, T4 or T3), occur prior to the occurrence of clinical signs. The majority of dogs that develop autoantibodies have them by 3 to 4 years of age. Development of autoantibodies at any time in the dog's life is an indication that the dog, most likely, has the genetic form of the disease. As a result of the variable onset of the presence of autoantibodies, periodic testing will be necessary. Dogs that are negative at 1 year of age may become positive at 6 years of age. Hence, dogs should be tested every year or two in order to be certain that they have not developed the condition. Since the majority of affected dogs will have autoantibodies by 5 years of age, annual testing for the first 5 years is recommended. After that, testing every other year should suffice. Unfortunately, a negative at any one time will not guarantee that the dog does not have autoimmune thyroiditis. The registry data can be used by breeders in determining which dogs are best for their breeding program. Knowing the status of the dog and the status of the dog's lineage, breeders and genetic counselors can decide which matings are most appropriate for reducing the incidence of automimmune thyroiditis in the offspring. [TOP] Examination Certification All data, whether normal or abnormal, is to be submitted for purposes of completeness. There is no OFA fee for entering an abnormal evaluation of the thyroid into the data bank. Information on dogs determined to be abnormal (positive or equivocal) will not be made public without the explicit permission of the owner or agent. Those dogs with laboratory results that are questionable and therefore not definitive, will be considered as equivocal. It is recommended that the test be repeated in 3 to 6 months. [TOP] Preliminary Evaluation Thyroid Abnormalities |
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Classification The method for classifying the thyroid status will be accomplished using state of the art assay methodology. Indices of thyroiditis: |
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Table 1. Diagnosis and Certification | |
Normal | FT4D = 9-40pmol/L |
cTSH = 0-30 mU/L | |
a | TgAA = negative |
Positive autoimmune thyroiditis | FT4D < 9 pmol/L |
a | cTSH > 30 mU/L |
a | TgAA = positive |
Positive compensative autoimmune thyroiditis | FT4D = 9-40 pmol/L |
a | cTSH = or > normal range |
a | TgAA = Positive |
Idiopathically reduced thyroid function | FT4D < 9 pmol/L |
a | cTSH > 30 mU/L |
a | TgAA = Negative |
All other results are considered equivocal. |
[TOP]
OFA-Approved Laboratories Laboratories may apply and if successful, will be approved to perform analyses for OFA thyroid certification. A site visit by a qualified veterinary endocrinologist chosen by OFA will be required and continued quality assurance and quality control will be necessary to maintain certification. Fully certified status can be obtained by passing the site visit and passing the results of the first OFA quality assurance assay result test. The approved laboratory must be contacted for the appropriate submission forms, sample handling procedures, and laboratory service fee before collecting the sample. The OFA thyroid application and check to OFA must accompany the serum sample to the laboratory of choice. Upon completion of test, the laboratory then forwards all appropriate paperwork to OFA. Currently, samples may be submitted to one of the following OFA-approved laboratories:
For more information, visit OFA's official website. [TOP] Contact OFA directly for specific information on the OFA registries:
Dr. R.A. Weitkamp ~ President
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Primary |
Those associated with the thyroid gland, i.e., a deficiency of Thyroxin-T4. |
Secondary |
Those associated with the pituitary gland, i.e., a deficiency of Thyroid Stimulating Hormone-TSH. |
Tertiary |
Those associated with the hypothalamus, i.e., a deficiency of Thyrotrophin-TRH. |
Table 2. Symptoms of Thyroxin (T4) Deficiency |
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Common |
Uncommon |
Unknown |
Skin changes Lethargy Weight gain Mental dullness Exercise intolernance |
Female infertility Neuromuscular signs Ocular changes Cretinism Myxedema |
Male infertility Clotting disorders cardiovascular changes Behavioral changes Gastrointestinal signs |
[Back to Background information] [TOP] I'd like to thank the Orthopedic Foundation For Animals for their permission to reproduce the Thyroid Registry brochure. [TOP]
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Last updated: Saturday, February 06, 2010 |
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