Canine Multifocal Retinopathy Type 1 and Type 2 (CMR1 and CMR2)
Description:
Canine Multifocal Retinopathy Type 1 and 2 (CMR1 and CMR2) is an autosomal recessive eye disorder known to affect Great Pyrenees, English Mastiffs, Bullmastiffs, Australian Shepherds, Dogue de Bordeaux, English Bulldogs, American Bulldogs, Coton de Tulears, Perro de Presa Canario, and Cane Corsos.
The mutation causes raised lesions to form on the retina. The lesions alter the appearance of the eye but usually do not affect sight. The lesions may disappear, or may result in minor retinal folding. Symptoms of the mutation usually appear when a puppy is only a few months old, and generally do not worsen over time.
CMR is a recessive disorder. This means that a dog must inherit two copies of the mutation in order to exhibit symptoms of CMR. A dog with one copy of the mutation is known as a carrier. If two carriers are bred to one another, there is a 25% chance per puppy born that they will develop symptoms of CMR and a 50% chance per puppy born that they will also be carriers. Therefore, it is useful to test for the presence of the CMR mutation before breeding. Additionally, since retinal defects can be caused by other conditions, testing can verify that a dog actually has CMR rather than some other eye condition.
Progressive Retinal Atrophy or PRA-prcd
Description:
Progressive Rod-Cone Degeneration, or PRA-prcd, is a form of Progressive Retinal Atrophy (PRA) in which the cells in the dog’s retina degenerate and die. PRA for dogs is similar to retinitis pigmentosa in humans. Most affected dogs will not show signs of vision loss until 3-5 years of age. Complete blindness can occur in older dogs. Progressive Rod-Cone Degeneration is a form of PRA known to affect over 40 different breeds.
The retina is a membrane located in the back of the eye that contains two types of photoreceptor cells. These cells take light coming into the eyes and relay it back to the brain as electrical impulses. These impulses are interpreted by the brain to “create” images. In dogs suffering from PRA-prcd, the photoreceptors begin to degenerate, causing an inability to interpret changes in light. This results in a loss of vision. Rod cells, which normally function in low-light or nighttime conditions, begin to degenerate first. This leads to night-blindness. The cone cells, which normally function in bright-light or daytime conditions, will deteriorate next. This often leads to complete blindness over a period of time.
PRA-prcd is inherited as an autosomal recessive disorder. A dog must have two copies of the mutated gene to be affected by PRA. A dog can have one copy of the mutation and not experience any symptoms of the disease. Dogs with one copy of the mutation are known as carriers, meaning that they can pass on the mutation to their offspring. If they breed with another carrier, there is a 25% chance that the offspring can inherit one copy of the mutated gene from each parent, and be affected by the disease.
Canine Cystinuria
Description:
Canine Cystinuria is an autosomal recessive disorder that affects a dog’s ability to filter cystine out of urine. Normally, tubules in the kidney are responsible for re-absorption of cystine, filtering it out of the urine. In dogs with Canine Cystinuria, the tubules are unable to transport the cystine, allowing it to accumulate in the urine. Cystine is generally insoluble in the acidic conditions of canine urine, allowing it to crystallize and form caliculi, also known as stones.
Not every dog that has the mutation responsible for Cystinuria will exhibit symptoms. Stones causing inflammation and blockage are often more common in males, due to their long, narrow urethra. Females exhibit symptoms much less frequently and may be completely asymptomatic.
Canine Cystinuria affects over 60 breeds of dogs. Research suggests that Newfoundlands carry a more severe form of this disease than other breeds. In a variety of breeds affected by Canine Cystinuria, symptoms are often not experienced until about 4-5 years in age. However, Newfoundlands may begin experiencing problems as early as 6 months to one year of age. Newfoundlands are much more likely to experience recurring urethral blockages that could require surgical intervention.
In the Newfoundland breed, the cause of Cystinuria is a single nucleotide polymorphism that occurs in the SLC3A1 gene which causes a premature stop codon. Cystinuria is a recessive disorder, meaning that the dog must have two copies of the defective gene to suffer from the disease. Because Cystinuria is a recessive disorder, a dog can also be a carrier of this disease, meaning it carries one copy of the mutation but does not display any symptoms. If two carriers are bred together, there is a 25% chance per puppy born that it will develop symptoms of Cystinuria.
Degenerative Myelopathy (DM)
Description:
Degenerative Myelopathy (DM) is a progressive neurological disorder that affects the spinal cord of dogs. Dogs that have inherited two defective copies can 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 10-12 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 can develop Degenerative Myelopathy, the disease does not affect every dog that has the genotype.
