Juvenile Addison's Disease (JADD) in Nova Scotia Duck Tolling Retrievers
Addison’s disease occurs when the adrenal glands stop secreting necessary natural steroid hormones. In the Nova Scotia Duck Tolling Retriever, a genetic form of Addison's disease can occur in puppies.
Phenotype: The clinical signs of Addison’s disease can include lethargy, lack of appetite, vomiting, and diarrhea. The average age of puppies affected by this juvenile form of Addison's disease is 5 months. Puppies can have other concurrent diseases including eye problems (corneal edema, conjunctivitis, or uveitis) that may require specialized treatment.
Mode of Inheritance: Autosomal recessive (incomplete penetrance)
Alleles: N = Normal, A = Juvenile Addison's disease (JADD)
Breeds appropriate for testing: Nova Scotia Duck Tolling Retriever
Explanation of Results:
Dogs with N/N genotype are not expected to have this form of juvenile Addison's disease and cannot transmit this JADD variant to their offspring.
Dogs with N/A genotype are not expected to have this form of juvenile Addison's disease, but are carriers. They will transmit this JADD variant to 50% of their offspring. If carriers are bred together or to an affected mate, affected offspring can be produced.
Dogs with A/A genotype have a 75% chance of developing Addison's disease by one year of age.
Addison’s disease (hypoadrenocorticism) occurs when the adrenal glands stop secreting the natural steroid hormones necessary for the regulation of glucose metabolism, immune function (glucocorticoids), sodium and potassium levels in the blood (mineralocorticoids). 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 ACTH stimulation test. The clinical signs of Addison’s disease can include lethargy, lack of appetite, vomiting, and diarrhea.
In the Nova Scotia Duck Tolling Retriever, or Toller, breed, a genetic form of this disease, called Juvenile Addison's Disease (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 mineralocorticoid and glucocorticoid replacement therapy. Puppies can have other concurrent diseases including eye problems (corneal edema, conjunctivitis, or uveitis) that may require specialized treatment.
Scientists from the Bannasch Laboratory at the University of California, Davis have developed a DNA test to identify carriers of JADD in the Toller breed. The juvenile form of Addison’s disease is genetically distinguishable from the adult onset form in that all dogs that develop the juvenile form have two identical copies of a specific region within their genome and a specific mutation within a novel gene. The mutation responsible for JADD causes a change in the amino acid sequence in a highly conserved region of this protein. This mutation is not present in any other breeds of dogs based on testing of over 250 individual animals in 80 different breeds.
JADD in Tollers is inherited as an autosomal recessive disease. Affected puppies inherit two copies of the defective gene, one 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. According to researchers, approximately 75% of puppies with two copies of the mutation will develop Addison’s disease. 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.
Breeders can use results from this test as a tool to select mating pairs to avoid producing affected dogs. At the time that the mutation was discovered, about 20% of Tollers were carriers (N/A) of JADD.
Normal. No copies of the JADD mutation are present.
Carrier. 1 copy of the JADD mutation is present. If carriers are bred together or to an affected mate, affected offspring can be produced.
Affected. 2 copies of the JADD mutation. Dog has 75% chance of developing Addison’s disease by 1 year of age.
Hughes, A.M., Jokinen, P., Bannasch, D.L., Lohi, H., & Oberbauer, A.M. (2010). Association of a dog leukocyte antigen class II haplotype with hypoadrenocorticism in Nova Scotia Duck Tolling Retrievers. Tissue Antigens, 75(6), 684-690. doi: 10.1111/j.1399-0039.2010.01440.x