Tollers are generally healthy. However, like almost all dog breeds, they have specific potential genetic disorders. Breeding stock should be tested for the following:
- Hip Dysplasia – an abnormal formation of the hip socket that can lead to severe arthritis and lameness.
- Collie Eye Anomaly (CEA) – an inherited disease causing defects in the formation of the eye.
- Progressive Retinal Atrophy (PRA) – a group of diseases that cause the retina of the eye to degenerate slowly over time.
- Juvenile Addison’s Disease (JADD) – a rare, early onset, chronic endocrine disorder in which the adrenal glands do not produce sufficient steroid hormones.
- Cleft Palate (CP1) – a birth defect whereby a hole in the roof of the mouth develops while the puppy is in utero.
THE DYSPLASTIC HIP JOINT
Hip Dysplasia is a terrible genetic disease because of the various degrees of arthritis (also called degenerative joint disease, arthrosis, osteoarthrosis) it can eventually produce, leading to pain and debilitation.
The very first step in the development of arthritis is articular cartilage (the type of cartilage lining the joint) damage due to the inherited bad biomechanics of an abnormally developed hip joint. Traumatic articular fracture through the joint surface is another way cartilage is damaged. With cartilage damage, lots of degradative enzymes are released into the joint. These enzymes degrade and decrease the synthesis of important constituent molecules that form hyaline cartilage called proteoglycans. This causes the cartilage to lose its thickness and elasticity, which are important in absorbing mechanical loads placed across the joint during movement. Eventually, more debris and enzymes spill into the joint fluid and destroy molecules called glycosaminoglycan and hyaluronate which are important precursors that form the cartilage proteoglycans. The joint’s lubrication and ability to block inflammatory cells are lost and the debris-tainted joint fluid loses its ability to properly nourish the cartilage through impairment of nutrient-waste exchange across the joint cartilage cells. The damage then spreads to the synovial membrane lining the joint capsule and more degradative enzymes and inflammatory cells stream into the joint. Full thickness loss of cartilage allows the synovial fluid to contact nerve endings in the subchondral bone, resulting in pain. In an attempt to stabilize the joint to decrease the pain, the animal’s body produces new bone at the edges of the joint surface, joint capsule, ligament and muscle attachments (bone spurs). The joint capsule also eventually thickens and the joint’s range of motion decreases.
No one can predict when or even if a dysplastic dog will start showing clinical signs of lameness due to pain. There are multiple environmental factors such as caloric intake, level of exercise, and weather that can affect the severity of clinical signs and phenotypic expression (radiographic changes). There is no rhyme or reason to the severity of radiographic changes correlated with the clinical findings. There are a number of dysplastic dogs with severe arthritis that run, jump, and play as if nothing is wrong and some dogs with barely any arthritic radiographic changes that are severely lame.
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JUVENILE ADDISON’S DISEASE (JADD) IN THE NOVA SCOTIA DUCK TOLLING RETRIEVER
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.
Scientists from the Bannasch Laboratory at the University of California, Davis have developed a DNA test to identify carriers ofJADD 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.
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.
- 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.
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.
CLEFT PALATE (CP1) IN THE NOVA SCOTIA DUCK TOLLING RETRIEVER
A cleft palate is a birth defect whereby a hole (cleft) in the roof of the mouth (palate) develops in a puppy during gestation. Puppies born with cleft palate can experience difficulty nursing which will greatly increase their risk of developing aspiration pneumonia – a serious life threatening condition. There are multiple genetic causes of cleft palate within the NSDTR breed; however, the most common form has been identified as CP1.
The mutation test we have developed identifies carriers of CP1 within the NSDTR breed. It does not apply to any breed other than the NSDTR. If you have a puppy of a different breed with cleft palate and you wish to participate in the identification of the gene(s) responsible please contact the Bannasch Laboratory at the University of California at Davis (firstname.lastname@example.org).
Scientists from the Bannasch Laboratory at the University of California, Davis have discovered the genetic cause of ONE FORM of cleft palate in the Nova Scotia Duck Tolling Retriever. Dogs with this form of cleft palate have a large insertion into a gene known to affect the proper development of the palate. This mutation is not present in any other breed based on testing conducted on over 300 individual animals of over 80 different dog breeds.
THE MODE OF INHERITANCE
Cleft palate caused by CP1 is a simple autosomal recessive disease meaning that an affected puppy has inherited one mutant copy of the gene from each parent.
- CP1 N/N This dog has two normal copies of CP1
- CP1 N/A This dog has one mutant (abnormal) copy of CP1
- CP1 A/A This dog has two mutant (abnormal) copies of CP1
In order to keep the cost of this test low the test will be run in batches of 48 which could affect the turnaround time for results.
CP1 is an inherited autosomal recessive disease. Animals that have only one mutant copy of CP1 (N/A) are normal but they are carriers of the disease. When two carriers are bred to each other the resulting puppies can be affected. At the time that this test was released, approximately 15% of Tollers were carriers of CP1 (N/A); however, the number of carriers can change with each generation.