|DOGS WITH HEART|
Collie Eye Anomaly (CEA)
Collies share Collie Eye Anomaly (CEA) with several other breeds ie the Sheltie. CEA is more technically known as Choroidal Hypoplasia (CH). It is a recessively inherited eye disorder that causes abnormal development of the choroid - an important layer of tissue under the retina of the eye.
Since the choroid layer does not develop normally from the start, the primary abnormality can be diagnosed at a very young age. Regrettably, there is no treatment or cure for CEA.
The primary problem is choroidal hypoplasia (CH). There is under-development (hypoplasia) of the eye tissue layer called the choroid. The choroid appears pale and thin, almost transparent, and the blood vessels of the choroid can easily be recognized in those “thin” areas. The ophthalmologist, looking at the back of the eye (the fundus) with an ophthalmoscope, typically will see an area of choroidal thinning that appears like a “window” to the underlying vessels and sclera.
MILD disease: Mild disease is very common in Shelties. It is easily recognizable on careful ophthalmologic examination as early as 5 to 8 weeks of age. Once the retina changes to its adult colour around 3 months of age, the normal pigment sometimes masks the changes in the choroid (so-called “go normal”). In mildly affected dogs, choroidal thinning is the only detectable abnormality and the dog retains normal vision throughout life. However, dogs with mild disease can produce severely affected offspring.
SEVERE disease: Colobomas are seen at and near the optic nerve head as outpouchings or “pits” in the eye tissue layers. Colobomas can lead to secondary complications such as partial or complete retinal detachments and/or growth of new but abnormal blood vessels with haemorrhage – bleeding inside the eye. This can affect either one or both eyes. Complications of severe disease can lead to vision loss, although this disorder only rarely threatens total blindness.
CEA/CH is not progressive in the usual sense. The essential features, choroidal hypoplasia and coloboma, are congenital – the abnormalities develop as the eye develops. These features are also stationary once ocular development is complete around 8-12 weeks. Retinal detachments and/or aberrant vessel formation can be congenital or develop later, in general only in eyes with colobomas.
BOTH the mild and severe forms of CEA/CH disease now are proven to result from the exact same gene and mutation in ALL of the affected breeds.
Multiple Drug Resistance (MDR1)
MDR1 is a mutant gene that occurs in some breeds which affects the canine's ability to pump certain systemic drugs out of the brain. Without this ability, drugs can reach toxic levels causing neurological symptoms. Sometimes these symptoms are mild and other times the symptoms are severe enough to lead to coma and death.
Your dog may start showing drooling, irritability, ataxia… things you would not immediately think of as a drug reaction.
Drugs that can cause reactions
Progressive Retinal Atrophy (PRA)
Researchers from Norwegian University of Life Sciences have identified a novel mutation in CNGA1 gene that causes early onset PRA in Shetland Sheepdogs .
PRA in Shelties is clinically indistinguishable from PRA in other breeds. As in other forms of PRA, it is characterized by visual impairment due to degeneration of the photoreceptors in the retina, eventually leading to blindness. Often the first sign of PRA apparent to an owner is night blindness however a veterinary ophthalmologist may detect the disease at an earlier stage of disease during routine clinical examination. Over time, the disease progresses to advanced PRA in which vision loss is evident even at bright light levels.
CNGA1-PRA is inherited as an autosomal recessive disease in Shelties which means that dogs will only develop this form of PRA when they inherit two copies of mutant DNA, one from each parent. Carriers of only one copy of the mutation will not develop the disease.
Degenerative Myelopathy (DM)
Degenerative Myelopathy in Shelties is an inheritable, recessive gene that can be passed on to future generations of puppies. What makes this a difficult disease to control is the fact that symptoms do not usually become evident until the dog is an older adult. This is long after a dog has been used for breeding multiple times.
The term Degenerative Myelopathy is descriptive of its effect on the dog. It wears away (degenerative) the myelin sheath (myelopathy) that surrounds the nerves of the spinal cord. As that protective covering around the nerves disintegrates, a variety of symptoms start showing.
The dog’s neurological function is slowly affected changing his ability to move normally, until he is unable to walk. He can also develop loss of control of bowel or bladder. Degenerative Myelopathy in Shelties is the dog’s version of Lou Gerig’s Disease.
There is no cure and there is no treatment other than palliative (keeping the dog comfortable). It is progressive and so the prognosis is poor. Many dogs with the disease may need to be euthanized.
Von Willebrand’s Disease Type III (VWD)
Von Willebrand's disease, an inherited bleeding disorder, usually comes in two major types, type I and type III. (There is also a rarer Type II, not relevant to Shelties). Type III is a severe bleeding disorder with a high risk of spontaneous bleeding as well as a risk of serious bleeding from trauma and surgery. It is probably best known in Scottish Terriers, Shelties & Kooikerhondjies. Type I is milder, with most of the risk coming from trauma or surgery. It is probably best known in Doberman Pinschers. The Sheltie breed has type III vWD, the severe type. There may also be a second less prevalent defect, causing some Shelties to have the less severe Type I vWD, but this is uncertain at present.
Primary Ciliary Dyskinesia (PCD)
Primary Ciliary Dyskinesia (PCD) is an inherited disorder of the cilia affecting some breeds. Cilia are microscopic, hair-like structures that line the nasal cavity, trachea, and bronchi of the respiratory system, the fluid filled cavities of the brain and portions of the reproductive tract. Normal cilia move in wave-like patterns to aid the movement of fluids in the brain and reproductive tracts and prevent large particles and pathogens from getting into the lungs. In PCD, affected dogs have cilia that are either malformed or do not move. Particles and pathogens cannot be removed from the upper respiratory tract and can lead to sinusitis, bronchitis and pneumonia. Affected dogs typically present a few days after birth with respiratory disease. Symptoms include coughing, sneezing, nasal discharge and frequent respiratory infections. This disorder also causes immobility of sperm, therefore affected male dogs are sterile. Dogs with PCD may also have a transposition of organs in the thoracic and/or abdominal cavities, resulting in a mirror image of the normal placement of the heart and lungs and sometimes other organs. This transposition is called situs inversus and does not usually cause clinical problems. Dogs with this disorder can live for years if their chronic respiratory infections are managed.
The cause…The first probable cause is genetics. It has been the thorn in the sides of breeders for decades now. Because there never seemed a simple inheritable pattern from parents to pups, it was felt to be polygenetic in nature. This means not one but several genes may play a role in whether a dog develops dysplasia. A specific gene has been found in the German Shepherd Dog, so finally there may be some objective means to determine which dogs to breed. It will take time to isolate the gene in other breeds but at least there is some progress.
It is thought that genes cause the hip to develop in a less than functional manner.
A hip that has greater laxity (stretching ability) means that the ball and joint don’t sit snugly together. That would give the two pieces the chance to bounce around and wear away bone in the wrong places whenever the joint moved. Wearing down bone causes pain and bone spurs and eventually hip dysplasia in dogs.
Depth of the socket is how deep does the ball of the femur sit in the socket. Even if it is a snug fit, a shallow socket can let the ball of the joint slosh around easier, and again wear away the socket in places it shouldn’t, like the edges.
This allows more and more movement in the wrong directions and again total wearing away of the joint.
A shallow hip joint can cause hip dysplasia in dogs as early as 4 to 6 months of age!
How a dog ages is another possibly hereditary factor. Osteoarthritis, usually develops as a dog ages. In the aging process, the cartilage loses protein and gains water making it softer and easier to wear away. Once the cartilage is gone, the bones rub against each other every time the joint is moved. This causes the bone to wear away, again causing pain and bone spurs.
In addition to the genetics, there is a big nature vs nurture aspect to this illness of hip dysplasia in dogs. A gene may be present but the right circumstances allow it to be expressed in that individual dog:
Obesity - more pressure on a joint and it will fail faster and easier than if less stress is placed on it.
Onset of Sports / Pattern of Exercise – Taking your puppy jogging long distances before they are mature and growth plates in the legs have closed (finished growing). Agility training the jumps. Repetitive jumping at a young age can cause damage to the joints.
Hip Dysplasia displays as lameness, or inability to bear weight on back legs, decreased range of motion in the back legs, loss of muscle tissue.
Elbow dysplasia in dogs is considered the leading cause of canine forelimb lameness. Elbow dysplasia is a general term meaning arthritis of the elbow, that encompasses several conditions of the elbow joint. All of these are causes of elbow dysplasia, but are different conditions with their own distinct pathophysiology:
Fragmented coronoid process – condition in which a small piece of bone on the inner side of the joint breaks off the ulna. The fragment irritates the joint and wears away the cartilage of the humerus.
Ununited anconeal process – condition in which a fragment of bone on the back side of the joint has failed to unite with the ulna during growth.
Osteochondritis dessicans – OCD is a condition in which a piece of cartilage becomes partially or fully detached from the surface of the elbow joint. This results in inflammation of the lining of the joint and causes pain.
Joint incongruity – a condition where the joint does not have the correct conformation and the cartilage of the joint wears out rapidly. This leads to progressive arthritis.