DNA Health Testing
In dogs affected with MDR1, the blood brain barrier is comprimised. This gene encodes a protein, P-glycoprotein, that is responsible for pumping many drugs and other toxins out of the brain. Dogs with the mutant gene can not pump some drugs out of the brain as a normal dog would, which may result in abnormal neurologic signs. The result may be an illness requiring an extended hospital stay--or even death. It is well known that all sizes of Australian Shepherds and related breeds can have adverse reactions to drugs such as ivermectin, loperamide (Imodium®), and others. DNA testing is now available through various laboratories in Europe.
Dogs that are affected by MDR1 will have a sensitivity to Ivermenctin and other related drugs.
Dogs that are carriers of MDR1 may experience some sensitivity to Ivermectin and other related dogs.
Dogs that test clear for MDR1 should not exhibit any drug sensitivities.
Here is a list of Medications that should be avoided if the status of an aussies MDR1 status is not known:
Acepromazine (tranquilizer and pre-anesthetic agent)
Butorphanol (analgesic and pre-anesthetic agent)
InIvermectin (antiparasitic agent)
Loperamide (ImodiumTM; antidiarrheal agent)
Selamectin, milbemycin, and moxidectin (antaparasitic agents)
Vincristine, Vinblastine, Doxorubicin (chemotherapy agents)
Drugs that are known to be pumped out of the brain by the protein that the MDR1 gene is responsible for producing but appear to be safely tolerated by dogs with the MDR1 mutation:Cyclosporin (immunosuppressive agent)Digoxin (cardiac drug)Doxycycline (antibacterial drug) Drugs that may be pumped out by the protein that the MDR1 is responsible for producing, but appear to be safely tolerated by dogs with the MDR1 mutation:Morphine, buprenorphine, fentanyl (opioid analgesics or pain medications)Inheritance:MDR1 is inherited as a recessive trait in most cases. This means a disease gene must be inherited from each parent in order to cause disease in an offspring. Parents were either clear, carrier or affected. A carrier has one disease gene and one normal gene, and is termed “heterozygous” for the disease. A normal dog has no disease gene and is termed "homozygous normal" - both copies of the gene are the same. And a dog with two disease genes is termed "homozygous affected" - both copies of the gene are abnormal.
The genetic disorder Progressive Rod-cone Degeneration-Progressive Retinal Atrophy, causes cells in the retina at the back of the eye to degenerate and die, even though the cells seem to develop normally early in life. The result is declining vision and eventual blindness. The “rod” cells operate in low light levels and are the first to lose normal function. Night blindness results. Then the “cone” cells gradually lose their normal function in full light situations. Most affected dogs will eventually go blind. It’s important to remember that not all retinal disease is PRA and not all PRA is the prcd form of PRA. DNA testing will make the diagnosis, prior to the onset of disease.
Inheritance: Prcd-PRA is inherited as a recessive trait in most cases. This means a disease gene must be inherited from each parent in order to cause disease in an offspring. Parents were either clear, carrier or affected. A carrier has one disease gene and one normal gene, and is termed “heterozygous” for the disease. A normal dog has no disease gene and is termed "homozygous normal" - both copies of the gene are the same. And a dog with two disease genes is termed "homozygous affected" - both copies of the gene are abnormal.
The typical inherited cataract in involves both eyes, and is present on the back side of the lens, these cataracts usually begin in an outer layer of the lens. Cataracts can usually be detected during a CERF eye exam on an adult, but they can appear at any age. The progression of cataracts varies in each dog diagnosed. Some progress very slowly that the dog will retain functional vision, if not full, throughout their lives. While others are so affected that they become blind in a very short period of time. Also some Aussies will develop cataracts in one eye while the other might not show any evidence for months. There is now a DNA test available for the presence of the HSF4 gene. As with prcd-PRA dogs can be clear, carriers or affected. All dogs testing as affected WILL develop cataracts and dogs tested as carriers are 17x more likely to develop cataracts.
CEA affected puppies appear normal. The defects are within the eye and cannot be detected without special instruments. Positive diagnosis can only be made by a veterinary ophthalmologist or with the DNA test. The specific defects the examiner will note are choroidal hypoplasia (chorioretinal dysplasia), optic nerve coloboma/staphloma and, rarely, retinal detachment. Both eyes will be affected but the specific defects may differ from eye to eye.
Some CEA puppies are masked affecteds. (This was once called "go normal.") They appear normal on exam because normal pigment development in the back of the eye sometimes covers the defective areas preventing observation. Masked affecteds have two copies of the mutation. Any offspring they produce will be carriers. It is important that all puppies be examined no later than 8 weeks of age to get them properly diagnosed.
CEA is present at birth and does not progress. CEA puppies behave normally. Few will be so blind that the disease noticeably affects them. CEA does not cause the puppy any pain or discomfort. Affected animals should never be bred; but if they are not blind they can live happy and productive lives.
Canine multifocal retinopathy (CMR) is a hereditary eye disease. CMR disease usually arises before 4th month of age in an affected puppy. Clinically, rose-grey coloured lesions are remarkable in retina. These lesions are of different size and shape and are occured in both eyes of affected individual. Total blindness usually comes in higher age.
Inheritance: CMR1 is inherited as a recessive trait in most cases. This means a disease gene must be inherited from each parent in order to cause disease in an offspring. Parents were either clear, carrier or affected. A carrier has one disease gene and one normal gene, and is termed “heterozygous” for the disease. A normal dog has no disease gene and is termed "homozygous normal" - both copies of the gene are the same. And a dog with two disease genes is termed "homozygous affected" - both copies of the gene are abnormal.
Cobalamin malabsorption refers to a genetic abnormality by which the vitamin B12, also known as cobalamin, fails to be absorbed from the intestine. This condition occurs secondary to the absence of a specific binding receptor in the lower intestine (the ileum) for intrinsic factor-cobalamin complex (IF-cbl). This is a rare disease.
Epilepsy in Australian Shepherds
Epilepsy is a seizure disorder. Both epilepsy and individual seizures can be caused by a variety of things: Head injury, toxic exposure, infections, fever, body chemistry imbalances and brain disease, to name a few. When a dog has a seizure, the veterinarians task is to identify and treat the cause. A detailed history will be taken to determine whether anything has happened to the dog that might cause seizures or whether it might be suffering from some other disease. Tests will be run to make sure blood counts and body chemistry are normal. An MRI might be done to see whether there is any damage or disease in the brain. If a cause is found, the dog will be treated for that problem. If permanent brain damage has not been done, treatment of the causative injury or disease will eliminate the seizures. If there is brain damage, the seizures may continue and require ongoing treatment. Such a dog would have secondary epilepsy brought about by an identified cause.
If a dog has inherited epilepsy, all tests will be negative. At this time there is no positive test for this disease. It is a diagnosis of exclusion the ruling-out of all other reasonable possibilities. Dogs with inherited epilepsy will continue to have seizures at intervals. The intervals may be as long as weeks to months or as short as once or several times in a single day.The dog cannot be cured. It will probably have seizures for the rest of its life.The seizures may cause cumulative damage to the affected area of the brain. And seizures sometimes kill.
It is important not to breed from any dogs that have produced offspring with epilepsy or are closely related to one that is affected or has produced an affected dog. Since we do not yet know how Epilepsy is inherited in Australian Shepherds it is important to research your lines to make sure no two dogs are mated together that have a history of epilepsy. Sometimes this can "jump" multiple generations (6+) and is therefore very difficult to predict. For more information please visit the dedicated homepage for health and genetics in Australian Shepherds
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