By Ray Nachreiner, DVM, PhD

Background

Autoimmune thyroiditis is the most common cause of primary hypothyroidism in dogs and is recognized as a heritable condition. Predisposed dogs are born with normal thyroid function and generally grow and develop in a normal manner. Evidence of an immune reaction in the thyroid glands begins to appear sometime in early adulthood in most affected dogs. The initiating factors remain unknown, but part of the response is the appearance of thyroid autoantibodies directed at thyroglobulin and sometimes the thyroid hormones, T4 and/or T3. Eventually the autoimmune response results in irreversible destruction of the thyroid glands, an inability to make thyroid hormones, and finally, development of clinical signs of hypothyroidism. This pathologic process may extend for several years in many affected dogs. Thus detection of positive thyroid autoantibodies early in the course of the disease serves to identify dogs at increased risk of becoming hypothyroid in the future.

Because 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 4 years of age, annual testing for the first 4 years is recommended. After that, testing every other year should suffice. Unfortunately, a negative at any one time will not guarantee that the dog will not develop thyroiditis.

The registry data can by 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 breedings are the most appropriate for reducing the incidence of autoimmune thyroiditis in the offspring.

General Procedures

Purposes -To identify those dogs that are phenotypically normal for breeding programs and to gather data on the genetic disease -autoimmune thyroiditis.

Examination and Classification -Each dog is to be examined by an attending veterinarian and have a serum sample sent to an OFA approved laboratory for testing according to the available application and general information instructions (see website http://www.offa.org) . The laboratory fee will be determined by the approved laboratory. Check with the referral laboratory for special requirements for sample handling and tests for registry purposes. Samples received within 48 hours do not have temperature requirements, but those in shipment for a longer period of time must be received at 60^oF or less.

Certification -A breed database number will be issued by OFA on all dogs found to be normal at 12 months of age or older. Ages will be used in the certification process since the classification can change as the dog ages and autoimmune disease progresses. It is recommended that reexamination occur at ages 2,3,4,6, and 8 years.

Preliminary evaluation -Evaluation of dogs under 12 months of age can be performed for private use of the owner since a few dogs are already positive at that age. However, certification will not be possible at that age.

Dogs with autoimmune thyroiditis -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 in the data bank. Information on results determined to be positive or equivocal will not be made public without the explicit written permission of the owner or agent.

Thyroid abnormalities fall into several categories -Two types will be defined by the registry.

                        Autoimmune Thyroiditis

                        Idiopathically Reduced Thyroid Function

 Autoimmune thyroiditis is known to be heritable.

Those dogs with laboratory results that are questionable -therefore, not definitive, will be considered as equivocal. It is recommended that the test be repeated in 3-6 months.