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 Test Results (PRA-PRCD) (PLL) (DM)

Progressive Rod-Cone Degeneration (PRA-PRCD)
Primary Lens Luxation (PLL)
Canine Degenerative Myelopathy (DM) 

Chinese Crested Progressive Rod Cone Degeneration (PRA-PRCD)

Progressive retinal atrophy (PRA) is a category of different progressive conditions related to ­retinal atrophy that can eventually lead to blindness.  Progressive rod-cone degeneration (PRA-PRCD) is one specific type of PRA that affects many dog breeds.  It is an inherited eye disease with late onset of symptoms that are due to degeneration of both rod and cone cells of the retina.  These cells are important for vision in dim and bright light.  Most dogs begin to show symptoms of the disease at approximately 3-5 years of age that manifests as difficulty seeing at night (night blindness) and loss of peripheral vision.  Although rate of onset and disease progression can vary by breed, PRA-PRCD typically results in eventual loss of sight and complete blindness in affected dogs.  It is important to note that other inherited eye disorders can display similar symptoms to PRA-PRCD.
RESULTS
 CLEAR/NORMAL: These dogs have two copies of the normal gene and will neither develop PRA-PRCD nor pass this mutation to their offspring.

CARRIER/NOT AFFECTED: These dogs have one copy of the normal gene and one copy of the mutation associated with this disease. They will not develop PRA-PRCD and will, if bred, pass the mutation to 50% of its offspring, on average.

AT RISK/AFFECTED: These dogs have two copies of the mutation associated with PRA-PRCD which typically results in complete blindness for most breeds.


Chinese Crested Primary Lens Luxation (PLL)

The lens of the eye normally lies immediately behind the iris and the pupil, and is suspended in place by a series of fibers.  It functions to focus light rays on the retina, in the back of the eye. When partial or complete breakdown of these fibers occur, the lens may become partially or fully dislocated from its normal position.   Lens luxation can occur for several different reasons.  Primary lens luxation is a heritable disease in many breeds and spontaneous luxation of the lens occurs in early adulthood (most commonly 3-6 years of age) and often affects both eyes, although not necessarily at the same time.  Lens luxation can lead to inflammation and glaucoma that can result in painful, teary, red eyes that may look hazy or cloudy. If detected early, surgical removal of the lens can be beneficial. Medical treatment of inflammation and glaucoma in the form of topical and oral medications can relieve much of the discomfort associated with this disease.

RESULTS

CLEAR/NORMAL: These dogs have two normal copies of DNA. Research has demonstrated clear dogs will not develop PLL as a result of the mutation, although it is possible they might develop PLL due to other causes, such as trauma or the effects of other, unidentified mutations.

CARRIER/NOT AFFECTED: These dogs have one copy of the mutation and one normal copy of DNA. Research has demonstrated that carriers have a very low risk of developing PLL. The majority of carriers do not develop PLL during their lives but a small percentage do. Current estimates are that between 2% – 20% of carriers will develop the condition.

AT RISK/AFFECTED: These dogs have two copies of the mutation and will almost certainly develop PLL during their lifetime. It is advised that all genetically affected dogs have their eyes examined by a veterinary ophthalmologist every 6 months, from the age of 18 months, so the clinical signs of PLL are detected as early as possible.


There are six different kinds of mating that could take place ignoring the sex of parents. These are shown below with expected proportions of progeny.​ 

For EXAMPLE if you were going to breed your Crested you would want 1. A x A =  both parents scoring an (A) if you were to breed 2. A x B you would only part with puppies as pet only unless you choose to test all puppies in the litter, because remember that 50% could be carriers and your puppies new owner decided to breed a carrier to another 25%of those puppy will be affected so be responsible if you choose to ever breed.    

As for purchasing a pet #4.5.6. could bring you heartache in many cases. And if purchasing a #3. there is that 2% chance that your puppy could be effected.  

Mating
 Normal (A)
 carrier (B)
 AFFECTED (C)
1. A x A
  100
  0
 0
2. A x B
  50
  50
  0
3. A x C
 0
 100
 0
4. B x B
 25
 50
 25
5. B x C
 0
 50
 50
6. C x C
 0
 0
 100

Canine Degenerative Myelopathy (DM)

Degenerative Myelopathy (DM) is a progressive disease of the spinal cord in older dogs. The disease has an insidious onset typically between 8 and 14 years of age. It begins with a loss of coordination (ataxia) in the hind limbs. The affected dog will wobble when walking, knuckle over or drag the feet. This can first occur in one hind limb and then affect the other. As the disease progresses, the limbs become weak and the dog begins to buckle and has difficulty standing. The weakness gets progressively worse until the dog is unable to walk. The clinical course can range from 6 months to 1 year before dogs become paraplegic. If signs progress for a longer period of time, loss of urinary and fecal continence may occur and eventually weakness will develop in the front limbs. Another key feature of DM is that it is not a painful disease.  Although any dog can be tested for DM, it is possible that the genetic background that predominates in some breeds prevents the development of symptoms even in dogs testing affected (at risk).  At this time the required evidence of association between the genetic mutation and actual spinal cord evaluations has only been proven in the breeds listed.

Genetic testing of the SOD1 gene in Chinese crested dogs will reliably determine whether a dog is a genetic Carrier of degenerative myelopathy. Degenerative Myelopathy is inherited in an Autosomal Recessivemanner in dogs meaning that they must receive two copies of the mutated gene (one from each parent) to develop the disease. In general, carrier dogs do not have features of the disease but when bred with another carrier of the same Mutation, there is a risk of having affected pups. Each pup that is born to this pairing has a 25% chance of inheriting the disease and a 50% chance of inheriting one copy and being a carrier of the SOD1 gene mutation. Reliable genetic testing is important for determining breeding practices. Because symptoms may not appear until adulthood and some at-risk/affected dogs do not develop the disease, genetic testing should be performed before breeding. Until the exact modifying environmental or genetic factor is determined, genetic testing remains the only reliable way to detect neurological disease associated with this mutation prior to death. In order to eliminate this mutation from breeding lines and to avoid the potential of producing affected pups, breeding of known carriers to each other is not recommended. Chinese crested dogs that are not carriers of the mutation have no increased risk of having affected pups.

Breed-Specific Information for the Chinese Crested

The Mutation of the SOD1 gene associated with degenerative myelopathy has been identified in the Chinese crested. The overall frequency of this disease in the breed and approximate age of disease onset are currently unreported for the Chinese crested. However, in one study of 53 Chinese crested dogs tested, 24.5% were carriers of the mutation.