Why Marble Mountain Kennels Does Genetic Testing

July 01

--By Pete Morrill, along with material copied and shared with permission

Why does Marble Mountain Kennels do testing for genetic issues?

Testing for a genetic health issue is helpful for a number of reasons: First and foremost, to ensure that we are doing everything we can to avoid genetically determined diseases in our puppies. Second, to help us make better breeding decisions. Third, To aid those who are using genetic testing to determine genetic markers for diseases.

In 2017 we started working with Embark, a leading organization in dog genetics, to test our dogs for 160 known canine diseases, 15 of which are specific to Labrador Retrievers. We also work with the Canine Eye Research Foundation (CERF), the Orthopedic Foundation for Animals (OFA), and the Canine Health Information Center (CHIC), all of which have at the heart of their mission the eradication of known hereditary problems in our canine friends.

We do three tests that require trained professional to do a physical evaluation of our dogs. OFA has a process to send in x-rays of a dog’s hips and elbows for review by a group of professional examiners. Most of our dogs get a preliminary evaluation at approximately 12 months of age and a final evaluation right after their second birthday. We also work with a specially trained animal ophthalmologist, who examines our dogs' eyes for abnormalities. These tests are sent to the Canine Eye Research Foundation, where dogs are certified to be free of abnormalities.

Generally, our first step is to collect a DNA sample and send it to Embark™. Embark's canine DNA test was designed to be the most comprehensive pet genetic test on the market. Developed by leading experts in dog and consumer genetics, the Embark canine DNA test tracks over 200,000 genetic markers, giving an extensive overview of both genetic disease risk and heritable traits. It is hoped that the information will help dog owners understand their pet’s health, plan for his future, and provide the best possible personalized care.

Below are the seven most common genetic problems found in Labs today. In 2017 Marble Mountain Kennels started testing for all of these issues and will continue to add to this number as genetic advances are made.

Hip Dysplasia

Hip Dysplasia is a terrible genetic disease because of the various degrees of arthritis it can eventually produce (including degenerative joint disease, arthrosis, and osteoarthrosis). These arthritic diseases lead to pain and complete debilitation.

The very first phase in the development of arthritis is articular cartilage damage (cartilage which lines joints). This damage is 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. The proteoglycans cause 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 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 which lines the joint capsule, resulting in more degradative enzymes and inflammatory cells streaming into the joint. Full thickness loss of cartilage causes 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 to form what are called 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 change correlated to 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 change are severely lame.

*Information provided by the Orthopedic Foundation for Animals website - http://www.offa.org

Elbow Dysplasia

The Three Faces of Elbow Dysplasia

Elbow dysplasia is a general term used to identify an inherited polygenic disease in the elbows of dogs. Three specific etiologies make up this disease and they can occur independently or in conjunction with one another. These etiologies include:

1. Pathology involving the medial coronoid of the ulna (FCP)

2. Osteochondritis of the medial humeral condyle in the elbow joint (OCD)

3. Un-united anconeal process (UAP)

Studies have shown the inherited polygenic traits causing these etiologies are independent of one another. Clinical signs involve lameness which may remain subtle for long periods of time. No one can predict at what age lameness will occur in a dog due to a great number of genetic and environmental factors, such as rate of weight gain, amount of exercise, etc. Subtle changes in gait may be characterized by excessive inward deviation of the paw which raises the outside of the paw so that it receives less weight and distributes more mechanical weight on the outside (lateral) aspect of the elbow joint away from the lesions located on the inside of the joint. Range of motion in the elbow is also decreased.

*Information provided by the Orthopedic Foundation for Animals website - http://www.offa.org

OFA Canine Eye Research Foundation (CERF) Eye Certification Registry

EYE CERTIFICATION REGISTRY OVERVIEW

The purpose of the OFA Eye Certification Registry (CAER) is to provide breeders with information regarding canine eye diseases so that they may make informed breeding decisions in an effort to produce healthier dogs. CAER certifications are performed by board certified (ACVO) veterinary ophthalmologists. Regardless of whether owners submit their CAER exam forms to the OFA for “certification,” all CAER exam data is collected for aggregate statistical purposes to provide information on trends in eye disease and breed susceptibility in dogs. Clinicians and students of ophthalmology, as well as interested breed clubs and individual breeders and owners of specific breeds will find this useful.

Portions of the material above have been reprinted with permission of the American College of Veterinary Ophthalmologists from the publication “Ocular Conditions Presumed to be Inherited in Purebred Dogs”, 5th Edition, 2010, produced by the Genetics Committee of the American College of Veterinary Ophthalmologists, © American College of Veterinary Ophthalmologists.

GENETICS OF INHERITED EYE DISEASE

Genetic diseases are those that are passed on from parent to offspring through genes that carry the codes for each specific trait. Many of the diseases and disorders that affect the eyes have genetic factors.

IDENTIFICATION OF INHERITED EYE DISEASES

Although there are noteworthy exceptions, most of the ocular diseases of dogs, which are presumed to be hereditary, have not been adequately documented. Genetic studies require examination of large numbers of related animals in order to characterize the disorder (age of onset, characteristic appearance, rate of progression, etc.) and to define the mode of inheritance (recessive vs. dominant). In a clinical situation, related animals are frequently not available for examination once a disorder suspected as inherited is identified in an individual dog. Maintaining a number of dogs for controlled breeding trials through several generations is a long and costly process. Both of these obstacles are compounded by the fact that many ocular conditions do not develop until later in life. Until the genetic basis of an ocular disorder is defined in a peer-reviewed published report, we rely on what statistical information is available from registry organizations, informed opinions, and consensus from ACVO diplomates. We must satisfy ourselves with terms like “presumed inherited” and “suspected to be inherited.” Several companies provide information on genetic testing and greatly assist in providing more information and data to aid in defining the canine genetics of ocular diseases.

There are eye diseases in the dog for which there is evidence of a genetic or heritable cause. The American College of Veterinary Ophthalmologists has listed ten of these diseases as automatic “fails." This means the affected dog is ineligible to receive an eye certification because of the significance of the condition to vision and/or the very strong evidence of heritability.

Portions of the material above have been reprinted with permission of the American College of Veterinary Ophthalmologists from the publication “Ocular Conditions Presumed to be Inherited in Purebred Dogs”, 5th Edition, 2010, produced by the Genetics Committee of the American College of Veterinary Ophthalmologists, © American College of Veterinary Ophthalmologists.

*Information provided by the Orthopedic Foundation for Animals website - http://www.offa.org

Exercise-Induced Collapse (EIC)

Exercise-induced collapse (EIC) is a genetic syndrome predominantly occurring in mixed breed dogs related to several retriever breeds, including purebred Labrador Retrievers. EIC also seen in Chesapeake Bay Retrievers and Curly Coated Retrievers, Boykin Spaniels, Cocker Spaniels, German wire-haired Pointers, Old English Sheepdogs, Bouvier des Flanders, Pembroke Welsh Corgis, and Clumber Spaniels (Verified 2015 by Laboklin in the UK). (Text from wikipedia.org) The EIC syndrome was first positively identified by DNA in Boykin Spaniels in 2010. Before that time, many owners misdiagnosed EIC episodes as heat stroke.

Dogs affected by EIC show signs of muscle weakness, loss of coordination, severe marked increase in body temperature, and life-threatening collapse when participating in strenuous exercise or activity. Affected dogs can tolerate mild to moderate exercise, but just 5 to 20 minutes of strenuous activity or even extreme excitement, such as that seen in field trials or hunt tests, can induce weakness or collapse. Dogs affected with EIC usually cannot continue with intense retriever training, but can live normal lives as house pets. As noted by the UMN, a few affected dogs have died during exercise or while resting immediately after an episode of EIC, so an affected dog's exercise should ALWAYS be stopped at the first hint of incoordination or wobbliness.

EIC is being observed with increasing frequency, either from the genetics becoming more widespread or from previously misdiagnosed cases being correctly identified now that there is evidence in the form of a DNA test. Dogs that have EIC are prone to mild to severe collapse that can range from dragging of the hind legs to complete collapse. Most affected dogs have been from field-trial breedings. Signs become apparent in young dogs as they enter heavy training, which is usually between 5 months and 7 years of age as stated in the initial UMN study in 2007. Dogs of either sex can be affected. Dogs with this condition are always normal at rest and are usually described as being extremely fit, prime athletic specimens of their breed.

NOTE: Nervous system, cardiovascular and musculoskeletal examinations are unremarkable as is routine blood analysis both at rest and during an episode of collapse.[1]

Centronuclear Myopathy (CNM or CM)

Centronuclear Myopathy (CNM), previously known as HMLR or Hereditary Myopathy, is an autosomal recessive mutation that causes insufficient muscle function in the Labrador Retriever breed. This is due to the centralization of the nuclei in muscle fibers caused by a missense insertion in the PTPLA gene.

Puppies with CNM are born apparently normal; however, it quickly becomes evident that there is a problem. The puppy will often not gain weight adequately due to decreased muscle tone in the esophagus. Within 2 to 5 months, the disease has usually progressed to display the full range of symptoms, including a loss of muscle tone and control, an awkward gait, and extreme exercise intolerance. This condition is exacerbated in cold conditions.

Unfortunately, there is no cure for CNM, as the dog will never develop properly functioning muscle tissue. The dog usually has a normal life span but he will always be plagued with the symptoms of CNM.

*This information was gathered from the Animal Genetics web-site http://www.animalgenetics.us/Canine/Genetic_Disease/CNM.asp

Progressive Retinal Atrophy (PRA)

Progressive retinal atrophy (PRA), also known as progressive rod and cone degeneration (PRCD), refers to a group of degenerative eye disorders that cause blindness in both eyes. The retina is a delicate membrane lining the back of the eyes. It is responsible for absorbing, reflecting and perceiving light, and is essential to vision. PRA isn’t well understood, although it probably is a genetic disorder. The first symptom of PRA is night blindness. Affected dogs are reluctant to go down stairs, go outside, navigate unfamiliar areas or jump on or off furniture in darkness or dim light. The surface of their eyes becomes cloudy and gray and may take on a greenish sheen. As the disease progresses, dogs bump into furniture and walls and stumble over familiar objects. Fortunately, retinal atrophy rarely is painful, and most dogs adjust to the progressive loss of vision. Owners should consult with their veterinarian to accurately diagnose and manage this condition.

SYMPTOMS OF PRA IN DOGS

  • Reluctance to jump on or off furniture during darkness
  • Night blindness (nyctalopia) or reduced vision in dim light
  • Sluggish pupilary light responses
  • Decreased menace response
  • Cloudy or opaque eye surface; grayish discoloration of the surface of the eye
  • Greenish sheen to the eye
  • Cataracts
  • Bumping into furniture or walls
  • Tripping or stumbling over objects
  • Pawing at the air when going down stairs
  • Reluctance to navigate stairs

*This information is taken from http://www.petwave.com.

Hereditary Nasal Parakeratosis (HNPK)

Hereditary nasal parakeratosis (HNPK) is an inherited autosomal recessive disorder found in Labrador Retrievers. A mutation T>G in the SUV39H2 gene causes the nose to dry out leading to chronic irritation and inflammation of the nose skin.

Symptoms of the disorder generally appear around 6 to 12 months of age. Affected dogs develop dry, rough, gray to brown crusts on the surface and edge of the nose. In some cases, painful cracks around and on the tip of the nose develop and, if not treated, develop superficial bacterial infections. Over time, the nose often begins to depigment, changing skin color from dark to light in color. Although the disorder is non-life-threatening, continuous care to reduce the recurrence of excessive nasal crusting is required throughout the life of the dog.

Because HNPK is a recessive disorder, a dog must have two copies of the mutation in order for the disease to manifest. This means that a dog can have one copy of the mutation and not experience any signs or symptoms of HNPK; this dog would be known as a carrier. The carrier can then pass on either the normal gene or the mutated gene to any offspring. If two carriers are bred, there is a 25% chance of having a dog that receives two mutated copies of the gene and would be affected by HNPK.

*This information was gathered from the Animal Genetics web-site http://www.animalgenetics.us/Canine/Genetic_Disease/CNM.asp


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