Juvenile Addison's Disease (JADD) in the Nova Scotia Duck Tolling Retriever (NSDTR)
Addison’s disease (hypoadrenocorticism) occurs when the adrenal glands stop secreting the natural steroid hormones (glucocorticoid) and hormones (mineralicorticoids) necessary for the regulation of sodium and potassium levels in the blood. Addison’s disease can occur in any breed of dog and it has an average age of onset of 4 years. Addison’s disease is diagnosed by a veterinarian using a blood test called an ACTH stimulation test. The clinical signs of Addison’s disease can include lethargy, inappetance, vomiting and diarrhea.
In the NSDTR, a genetic form of this disease, called JADD, occurs in much younger animals. The average age of puppies affected with JADD is 5 months; however, puppies as young as 8 weeks and as old as 12 months of age have been identified.
Treatment of puppies affected with JADD requires both mineralicorticoid and glucocorticoid replacement therapy. Puppies can have other concurrent diseases including eye problems (corneal edema, conjunctivitis or uveitis) that may require specialized treatment.
Discovery:
Scientists from the Bannasch Laboratory at the University of California, Davis have developed a DNA test to identify carriers of JADD in the Nova Scotia Duck Tolling Retriever. The juvenile form of Addison’s disease is genetically distinguishable from the adult onset form in that all dogs who develop the juvenile form have two identical copies of a specific region within their genome. Our lab has identified numerous markers within this region and we have compiled these markers into a haplotype based test in order to identify dogs that carry JADD. We believe that in addition to the markers that distinguish affected puppies from unaffected ones, the actual mutation responsible for JADD is included in this haplotype test.
The mutation responsible for JADD causes a change the amino acid sequence in a highly conserved region of a protein. This mutation is not present in any other breeds of dogs based on testing of over 250 individual animals in 80 different breeds. However, additional research is needed to demonstrate how this mutation causes JADD in Tollers. We offer the test now to help breeders avoid producing affected puppies while we continue to understand the mechanism of the mutation. Please contact researchers if you have an affected puppy and would like to participate in the project (dlbannasch@ucdavis.edu).
The mode of inheritance:
This form of the disease is inherited as an autosomal recessive disease meaning that affected puppies inherited one mutant copy of this gene from each of their parents. In addition, JADD is not completely penetrant meaning that not all puppies with two copies of the mutation will go on to develop the disease. Based upon our research, approximately 75% of puppies with two copies of the mutation and haplotype will develop Addison’s disease.
The test:
- JADD Probable N/N This dog has two normal copies of the JADD region
- JADD Probable N/A This dog has one mutant (abnormal) copy of the JADD region
- JADD Probable A/A This dog has two mutant (abnormal) copies of the JADD region and has a 75% chance of developing Addison’s disease by 1 year of age.
In order to keep the costs of this test low it will be run in batches of 48 samples which could affect the turnaround time for results.
Counseling:
JADD is inherited as an autosomal recessive disease meaning that animals have only one mutant copy of the region (N/A) are normal but they are carriers of the disease and they can produce affected puppies if bred to an affected dog (A/A) or another carrier (N/A). At the time that this test was released approximately 20% of Tollers carry JADD (N/A); however, the number of carriers can change with each generation. Dogs that are carriers (N/A) are normal themselves and can be safely bred to N/N dogs in order to maintain diversity within the breed and select for other positive attributes in carrier dogs.
