CAMARRRO SHETLAND SHEEPDOGS

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Genetic Testing Explanations

vWD3  von Willebrand Disease Type III

Type III von Willebrand Disease (vWD) is a very severe form of the disease in which affected animals do not produce any von Willebrand Factor protein in their blood. This condition makes them more likely to bleed abnormally and severely. This can lead to life threatening consequences in situations such as accidental injuries, spaying, or neutering. Because it is an autosomal recessive disorder, Shetland Sheepdogs, Scottish Terriers and Kooikerhondje that are "Carriers" of the disease show no signs of vWD, yet can pass the gene along and perpetuate the disease through breeding. Without testing, the potential result is more affected animals.

Although there is a significant frequency of vWD in Shelties and Scotties, no effective treatments exist. Responsible breeders have attempted to use factor assay, protein-based tests for vWD but have been unsuccessful in reducing the frequency of the disease. There are simply too many variables, such as estrus and thyroid function which produce variation in test results, making these approaches less than ideal. Therefore, breeders have heretofore been unable to combat the disease by using responsible breeding strategies to reduce the incidence of vWD in future generations of dogs.

MDR1  Multi-Drug Resistance Gene

MDR1 Multi-Drug Resistance Gene, (MDR) codes for a protein that is responsible for protecting the brain by transporting potentially harmful chemicals away from the brain. In certain breeds, a mutation occurs in the MDR1 gene that causes sensitivity to Ivermectin, Loperamide, and a number of other drugs. Dogs with this mutation have a defect in the P-glycoprotein that is normally responsible for transporting certain drugs out of the brain. The defective protein inhibits the dog's ability to remove certain drugs from the brain, leading to a buildup of these toxins. As a result of the accumulation of toxins, the dog can show neurological symptoms, such as seizures, ataxia, or even death.

Dogs that are homozygous for the MDR1 gene (meaning that they have two copies of the mutation) will display a sensitivity to Ivermectin and other similiar drugs. These dogs will also always pass one copy of the mutation to all potential offspring. Dogs that are heterozygous (meaning they have only one copy of the mutation) can still react to these drugs at higher doses. Also, there is a 50% chance that a dog with one copy of the mutation will pass it on to any offspring.

There are many different types of drugs that have been reported to cause problems. The following is a list of some of the drugs:

Ivermectin (found in heartworm medications) Loperamide (Imodium over the counter antidiarrheal agent) Doxorubicin, Vincristine, Vinblastine (anticancer agents) Cyclosporin (immunosuppressive agent) Digoxin (heart drug) Acepromazine (tranquiliser) Butorphanol ("Bute" pain control).

The following drugs may also cause problems: Ondansetron, Domperidone, Paclitaxel, Mitoxantrone, Etoposide, Rifampicin, Quinidine, Morphine.

CEA  Collie Eye Anomaly

Collie Eye Anomaly (CEA) is a inherited bilateral eye disease common in a number of breeds of dogs. The disorder causes abnormal development in layers of tissue in the eye under the retina called the choroid. These changes cause what is referred to as Choroidal Hypoplasia. The abnormal choroid appears pale and translucent. In most cases CEA is present at birth and can be detected in puppies as young as 4-8 weeks of age. There is currently no treatment for this disease.


DM  Degenerative Myelopathy

Degenerative Myelopathy (DM) is a progressive neurological disorder that affects the spinal cord of dogs. Dogs that have inherited two defective copies will experience a breakdown of the cells responsible for sending and receiving signals from the brain, resulting in neurological symptoms.

The disease often begins with an unsteady gait, and the dog may wobble when they attempt to walk. As the disease progresses, the dog's hind legs will weaken and eventually the dog will be unable to walk at all. Degenerative Myelopathy moves up the body, so if the disease is allowed to progress, the dog will eventually be unable to hold his bladder and will lose normal function in its front legs. Fortunately, there is no direct pain associated with Degenerative Myelopathy.

The onset of Degenerative Myelopathy generally occurs later in life starting at an average age of about 10 years. However, some dogs may begin experiencing symptoms much earlier. A percentage of dogs that have inherited two copies of the mutation will not experience symptoms at all. Thus, this disease is not completely penetrant, meaning that while a dog with the mutation is likely to develop Degenerative Myelopathy, the disease does not affect every dog that has the genotype.


CNGA1-PRA  Sheltie Progressive Retinal Atrophy

Sheltie Progressive Retinal Atrophy is an inherited disorder that belongs in group of eye disorders known as progressive retinal atrophy. Progressive retinal atrophy (PRA) includes autosomal recessively inherited diseases that lead to degeneration of retinal photoreceptor cells in dogs and other pets. It is a canine equivalent to retinitis pigmentosa (RP), an inherited eye disorder affecting human beings. The first case of PRA was observed in England more than hundred years ago.

In general, PRA is characterized by disturbance of vision in dark, visual field defects, and abnormalities in the electroretinogram. It appears in both eyes simultaneously. The age of onset and rate of retinal degeneration varies between the different forms of the conditions. Some forms of PRA are common to multiple dog breeds, while others are recognized in just a single breed. Until now, it has been identified in more than 100 dog breeds. Almost all forms of PRA are inherited in a recessively manner, with exceptions in some breeds such as Old English Mastiffs, Bullmastiffs, Siberian Husky and Samoyed where forms of PRA are inherited as dominant or X-linked disorders.

There are two types of photoreceptors in the eye, rods and cones. Rods have an important role for vision in dim light and also night vision. PRA causes rode degeneration and in this way leads to night blindness. Researchers estimated that PRA causes death of around 95% of the dog’s photoreceptors. Dog owners or breeders recognize PRA by ”glow” or ”increased shine” in the eyes. The disease is progessive. Initial stage is characterized by night blindness, while advanced stage of PRA can cause full blindness in the dog. After the appearance of first symptoms, it usually takes one year for the disorder to progress from initial to the advanced stange, causing severe and irreverisble damage to the dog’s eye.

Sheltie Progressive Retinal Atrophy (CNGA1-PRA) is a form of PRA with an adult onset, with average of developing first symptoms at 5 years of age.


Genetics

Sheltie Progressive Retinal Atrophy (CNGA1-PRA) is an inherited autosomal recessive disease. It is caused by a mutation in CNGA1 (cyclic nuceotide gated channel alpha 1) gene. This gene encodes for protein expressed in the outer segment of rod photoreceptors in the retina. The mutation is a 4 base pair deletion, which results in premature stop codon and expression of truncated protein.

Dog can be clear, carrier or affected. Carriers of the gene are heterozygous and do not develope the disease’s symptoms. When mating two carrier dogs, each future cub has a 25% chance of being affected, a 50% chance of being an asymptomatic carrier, and a 25% chance of being unaffected and not a carrier.


DMS  Dermatomyositis

Dermatomyositis (DMS)* is an autoimmune disease of the skin and muscle that occurs in both humans and dogs. In dogs, DMS is most often diagnosed in Shetland Sheepdogs and Collies and is caused by a combination of environmental and genetic factors. Skin lesions consist of hair loss and crusts on areas with minimal muscle overlying the bone such as the face, ear tips, legs and feet, and the tip of the tail. Muscle involvement is uncommon in Shelties. Onset of lesions may occur as early as 12 weeks of age or in mature dogs. In some affected puppies, lesions may diminish with age and may or may not return at an older age. Stress may induce worsening of lesions. Definitive diagnosis can only be made with a skin biopsy. Treatment with pentoxyphyline (Trental®), corticosteroids, and vitamin E has been helpful in some dogs.