CATALOGUE OF GENETIC DISEASES/DEFECTS
COMMONLY FOUND IN
THE CHOW CHOW BREED
Compiled & edited by Judith-Ann Robertson for distribution by the Chow Chow Club of Victoria and its members.
INTRODUCTION
The information found in this catalogue has been drawn from a number of sources, with the original list of genetic defects specific to Chows found in The Canine Consumer Report(1). From this list, the names and definitions of genetically transmitted diseases associated with the Chow Chow breed were extracted, categorised and further researched to provide basic information about the condition. The list of these conditions with their definition and relevant research information, where appropriate, are listed below.
The Canine Consumer Report provides a list of 148 purebred dog breeds, each of which is accompanied by a list of the identified genetically transmitted diseases that occur in purebred dogs. The disease and defects listed herein are to provide the breeder and owner of potential problem areas. All breeds and crosses have potential problems; however, with responsible preeding programs, together with education about the breed and its potential problems,many of the conditions listed can be reduced and hopefully eliminated from the breeding pool.
Disclaimer
This catalogue is in no way intended to imply that all Chow Chows are likely to exhibit any or all of the problems identified to this breed. However, it is through awareness of these and other problems and conditions wherein successful breeding programs can be initiated to rectify and eliminate those that are known to be genetically transmitted.
This catalogue was developed to provide a listing and descriptions of the existing congenital and hereditary diseases found in Chows and to describe other common conditions that are thought to be genetic in origin because they appear with higher-than-expected frequency in the breed. The knowledge of and experience with non-human animal diseases is always changing, and new diseases are discovered each year. As a result, this catalogue cannot be fully complete. Every attempt has been made, nevertheless, to provide the latest information from published articles in scientific and popular journals, from review chapters written by veterinary and other professionals, and from breed-club literature provided by designated representatives of individual breed clubs.
The conditions listed in the Canine Consumer Report occur with varying degrees of frequency and severity from one breed to the next. Hip dysplasia, umbilical hernias, and allergies, for example, are common conditions found in many breeds, while serious malformations and life-threatening conditions are found with less frequency. The impact of a particular disorder on the health and longevity of the breed or breeds that it affects will depend on the nature and severity of that disorder. Therefore, there has been no attempt to assign priority among the diseases identified in this catalogue. This sort of information should be sought from veterinarians and other medical professionals with relevant experience and from breed-club representatives.
OCULAR(2, 5, 7)
Cataract: As in humans, a change in structure of the lens of the eye leading to cloudiness and usually to blindness. Lens opacity which may affect one or both eyes and may involve the lens partially or completely. In cases where cataracts are complete and affect both eyes, blindness results.
Breeding is not recommended for any animal demonstrating partial or complete opacity of the lens or its capsule. The prudent approach is to assume cataracts to be hereditary except in cases known to be associated with trauma (eg. toxic substance in eye); other causes of ocular inflammation; specific metabolic diseases (eg. diabetes); PPMs; persistent hyaloid or nutritional deficiencies; or senile degeneration.
Distichiasis: Eyelashes abnormally located in the eyelid margin which may cause ocular irritation. Distichiasis may occur at any time in the life of the dog.
Distichiasis is the abnormal growth of an eyelash from the meibomian glands along the eyelid margin. This positions them directly out of the lid margin and they contact the eye surface due to this. The harm this causes depends on the stiffness of the eyelash that grows, the number of them and their exact position.
Untreated, distichiasis can lead to corneal ulcers, chronic eye pain, excessive tearing, and eyelid spasms. It is almost certainly uncomfortable for the dog and permanent removal of the offending eyelashes is best when any clinical signs are present.
Surgery is done in a number of ways, depending on the number of lashes present and the preferences of the surgeon. Cryosurgery (freezing of the lid margin at the affected sites) can sometimes be done with a local anaesthetic in a cooperative dog. There are other surgical options. Almost any surgery for this condition should be done with an operating microscope or good magnification so many general practitioners refer these cases to veterinary ophthalmologists.
Post-operative care of inflammation from the surgery is usually necessary and should be planned for. There are usually two or three follow-up visits to check for regrowth of the eyelashes and removal of any that return or persist. In most cases, this can be treated with success. This makes life much more comfortable for your dog.
Although the hereditary basis has not been fully established, it is probable due to the high incidence in some breeds. Because distichiasis is felt to be a recessive trait, breeder discretion is urged and affected dogs used for breeding should only be bred to lines clean of the same traits in order to dilute the genetic problem.
Ectropion: an abnormal rolling out of the eyelids.
Ectropion is the medical term used to describe sagging and outward turning of the lower eyelid and eyelashes. The margin of the eyelid and the eyelashes evert (turn out). This rubbing can lead to excessive tearing, crusting of the eyelid, mucous discharge and irritation of the eye.
During blinking, the eyelids normally sweep across the surface of the cornea (Tearing occurs because the eyelids are not able to wipe the surface of the cornea properly to pump the tears into the tear duct.
In Chows and other heavy headed breeds, ectropion can be present at birth and become more apparent as the animal ages. Some cases of ectropion are due to relaxation of the tissues of the eyelid as a result of aging. Some cases result from scarring of the inner surface of the eyelid caused by chemical and thermal burns, inflammatory diseases such as ocular pemphigoid, or allergic reactions.
Ectropion should be repaired surgically before the rubbing damages the cornea by causing infection and scarring. Prior to surgery, the eye can be protected by taping the lower lid down and using lubricating drops and ointment. In some cases, sutures can be placed through the lower eyelid until more definitive surgery can be performed.
The surgery to repair entropion will tighten the eyelid and its attachments. An antibiotic ointment is normally used for about a week. After the eyelids heal, the eye will not longer have the risk of corneal scarring, infection, and loss of vision.
Entropion: an abnormal rolling in of the eyelid. If your Chow tears more than you feel is normal, he may have "entropion". If your Chow tears excessively, consult your veterinarian
Entropion is the medical term used to describe rolling inward of the lower eyelid and eyelashes towards the eye. The skin of the eyelid and the eyelashes rub against the cornea (the front part of the eye) and conjunctiva (the mucous membrane that protects the eye). This rubbing can lead to excessive tearing, crusting of the eyelid, mucous discharge, a feeling that something is in the eye, irritation of the cornea, and impaired vision.
In Chows and other heavy headed breeds, entropion can be present at birth and become more apparent as the animal ages. Some cases of entropion are due to relaxation of the tissues of the eyelid as a result of aging. Some cases result from scarring of the inner surface of the eyelid caused by chemical and thermal burns, inflammatory diseases such as ocular pemphigoid, or allergic reactions.
Entropion should be repaired surgically before the rubbing damages the cornea by causing infection and scarring. The surgery to repair entropion is usually performed to tighten the eyelid and its attachments. An antibiotic ointment is commonly used for about a week following surgery. After the eyelids heal, the eye will feel comfortable and there should no longer exist the risk of corneal scarring, infection, and loss of vision.
Glaucoma: abnormally high pressure in the eye. This is a condition where the pressure of the fluid in the eye increases until the sight is gone in that eye. If it strikes one eye, the other eye is likely also to be affected. Glaucoma is one of the leading causes of blindness in dogs. Any underlying problem that increases the fluid pressure inside the eye is the culprit; most of the time this is due to inadequate drainage of fluid from the eye (as opposed to overproduction of fluid). In some breeds, including the Chow, glaucoma has been found to be hereditary
Signs of glaucoma include reddened conjunctival tissue (red eye), weeping, light sensitivity, or even enlargement of the eye. As pressure increases, the pupil can become dilated and the cornea cloudy. In the earliest stages, the owner of the dog may notice that the eyes have a glassy look or seem to be dilated more than normal for the amount of light available. It is at this point that the eye must be evaluated by a veterinarian who can measure the pressure in the eye. Early diagnosis is critical to save the vision of the dog, and involves treating the underlying causes of the increased pressure if at all possible.
As the pressure in the eye, also known as the intraocular pressure or IOP, rises above normal the lens may be torn from its attachments and become loose within the eye. This can cause serious problems including damage to the cornea. Once the retina is damaged and the sight is gone the options are as follows:
Pannus, aka chronic immune mediated keratoconjunctivitis sicca (CIKS): An immunologic eye disease characterised by abnormal growth of tissue over the cornea.
The cause of this condition is not known, at present. This may be an immune response to changes brought on by ultraviolet radiation. This is based on the increased prevalence of the disease at higher altitudes. Usually immune mediated CIKS starts at the outer edges of the cornea as blood vessel infiltration and then pigmentation of the cornea.
As the disease progresses it spreads across the cornea to the nasal side of the eye and blindness can result from the condition. The third eyelid may become thickened and depigmented, which makes the eye look even worse. If the disease appears early in life (less than 2 yrs. old), it has a tendency to be very severe as it progresses. When it shows up later in life (4 to 5 yrs. or older) it usually is less severe. CIKS can be controlled with medical therapy, usually very successfully. It can not be cured, however. Medication is necessary lifelong for dogs with this condition.
In areas of low elevation, it is usually possible to treat this with corticosteroid eye drops. In severe cases, injections of corticosteroids into the tissues surrounding the eye can be necessary. In areas of higher elevation it can be necessary to go to much greater lengths to control this problem.
Irradiation of the cornea, surgical removal of the affected areas of the cornea and other measures may be necessary to provide relief from this problem. (Chronic Superficial Keratitis (inflammation)) Pannus is an eye condition in which blood vessels grow onto the cornea. It can lead to blindness if untreated. It is not curable, but is controllable with medication. Some studies suggest an autoimmune problem.
Persistent pupillary membrane: a developmental abnormality where the membrane forming the iris does not form properly. Persistent blood vessel remnants in the anterior chamber of the eye which fail to regress normally in the neonatal period. These strands may bridge from iris to iris, iris to cornea, iris to lens, or form sheets of tissue in the anterior chamber. The last 3 forms pose the greatest threat to vision and when severe, vision impairment or blindness may occur.
Usually breeder option, although there are some breeds in which the problem is so severe that affected dogs should not be bred (eg. Chow Chow, Basenji). Certain PPM conditions can lead to further disorders such as cataracts or corneal opacity; these may result in advice that the dog not be bred. Otherwise, advice is the same as for distichiasis.
Progressive retinal atrophy: (PRA): a degenerative disease of the retinal visual cells which progresses to blindness. This abnormality may be detected by electroretinogram before it is apparent clinically. In all breeds studied to date, PRA is recessively inherited.
Breeding is inadvisable where there is bilaterally symmetric retinal degeneration (considered to be PRA unless proven otherwise).
INTERNAL(1,3,8)
Bloat: a condition where a dog's stomach produces excessive gas and enlarges severely enough to cause death without immediate treatment. Usually associated with gastric torsion.
Cerebellar hypoplasia: a condition where the cerebellum, a part of the brain, is poorly formed (too small or absent) and doesn't function properly or at all. Indications: abnormal gait and loss of control starting at 12 weeks. Thought to be genetic.
Cerebellar hypoplasia is a condition resulting from lack of development of the cerebellum during gestation (development) of the puppy. The dam was infected with a virus called panleukopenia. This virus disrupts the development of the brain, specifically the cerebellum. This condition is non-progressive. The cerebellum is necessary for fine motor control of muscles and balance. Animals with mild to moderate symptoms of the problem can live a fairly long live as long as they don't develop two problems from trauma or aspiration (inhaling of food on water) leading to pneumonias. Patience and love goes a long way in maintaining the quality of life for these animals afflicted with cerebellar hypoplasin.
The cerebellum is the portion of the brain responsible for the control of motion. When a puppy or kitten is born with an underdeveloped cerebellum, the condition is known as congenital cerebellar hypoplasia. There are infectious causes of this condition in both cats (panleukopenia infection prior to birth) and dogs (herpes virus infection prior to birth). Improper development of the cerebellum may occur due to injury, poisoning or just from an accident in development in the uterus. It is generally possible to see signs of this condition almost as soon as the puppy or kitten is born. Affected animals have tremors and unusual jerky movements or may fall down when they try to move. The symptoms do not get worse as they age. As the kitten or puppy grows it will learn to compensate for its condition but there are usually lifelong signs of a decreased ability to coordinate movement. Almost all dogs and cats with congenital cerebellar hypoplasia can live happily as pets with a little special care to compensate for their disabilities. This condition can be confused with cerebellar abiotrophy, a different disorder in dogs in which the puppy has a normal cerebellum at birth but it gradually dies. Signs of disease identical to cerebellar hypoplasia occur but the timing is different. Puppies with this condition seem normal at birth but usually start to show signs of problems after they are 2 months or more of age.
Hypomyelinogenesis: failure of the nervous system to form myelin, seen at birth.
Hyposomatotropism: failure of the body growth hormones (somatomedins) to develop fully. Also known as growth hormone- responsive dermatosis. Common in Pomeranians. Hyposomatotropism may or may not have a role in the development of alopecia.
Hypothyroidism(8): a common endocrine disease where the body produces an abnormally low amount of thyroid hormones. An autoimmune destruction of the thyroid gland which affects more than 50 dog breeds. The term hypothyroidism has been loosely applied to describe all stages of this disease process whereas strictly speaking it should be reserved for the end-stages when the animal's thyroid gland is no longer capable of producing sufficient hormone(s) to sustain clinical health. At this point, the dog can express any number of the non-specific multi-system signs of thyroid dysfunction. .(See lympocytic thyroiditis and thyroiditis below)
Clinical Signs of Canine Hypothyroidism
A concerted effort needs to be made by dog breeders and owners to screen breeding stock for evidence of thyroid dysfunction prior to their use as stud dogs and brood bitches. This is important because their legacy carries the genetic material for the current and future decades. Therefore, breeding from animals diagnosed with thyroid disease of any type is not recommended.
Intestinal malabsorption: a disease where the intestinal tract does not absorb nutrients properly. Also known as protein- losing enteropathy as a consequence of inflamatory bowel disease. In Chows, there can also be a wheat-sensitive and/or soy-sensitive and/or corn-sensitive enteropathy.
Lymphocytic thyroiditis(8): an autoimmune disease causing inflammation and destruction of the thyroid gland, which becomes infiltrated with lymphocytes (white blood cells) and leads to hypothyroidism. This is the most common endocrine disease of the dog and has an inherited predisposition (see hypothyroidism above and thyroiditis below).
Thyroiditis(8): an autoimmune inflammatory disease of the thyroid gland. The most common cause of canine thyroid disease is autoimmune thyroiditis (estimated 90% of cases). Thyroiditis is an immune-mediated process that develops in genetically susceptible individuals and is characterised by the presence of antithyroid antibodies in the blood or tissues. Thyroiditis is believed to start in most cases around puberty, and gradually progress through mid-life and old age to become clinically expressed hypothyroidism once thyroid glandular reserve has been depleted. During this process, the animal or person becomes more susceptible to immune-mediated or other diseases affecting various target tissues and organs. The prerequisite genetic basis for susceptibility to this disorder has been in established in humans, dogs and several other species. (See hypothroidism and lymphocytic thyroiditis above)
MUSCULAR-SKELETAL(1,3,4,9)
Cleft palate: a condition where the roof of the mouth is not closed and the inside of the nose opens into the mouth.
Elbow dysplasia: an abnormal development of the elbow joint. Elbow dysplasia is characterised by an onset of severe lameness at between 4 and 6 months of age. It almost always affects only one of the elbows but occasionally will affect both. There are three different types of elbow dysplasia: UAP (ununited anconeal process), FCP (fractured coronoid process), and OCD (osteochondrosis). OCD more resembles arthritis in the elbow that may or may not be brought on by trauma or looseness of ligamentation at the elbow. Final diagnosis can only be made by radiograph.
Elongated soft palate: the soft palate is abnormally long and causes breathing disorders.
General Information:
The soft palate is the rear, softer portion of the roof of the mouth. Occasionally dogs are born with an abnormally long soft palate that covers the opening to the windpipe to various degrees. The elongated palate eventually becomes swollen and inflamed, and further impairs breathing. Signs of elongated soft palate include difficult and/or noisy breathing, frequent gagging or choking, difficult swallowing, and coughing after eating or drinking.
Treatment Information:
The condition can be corrected by surgical shortening of the soft palate and widening of the nostrils. If you feel that this might be an option for you and your pet, your veterinarian will be happy to discuss the surgery with you.
Hip dysplasia (HD): a developmental malformation or subluxation of the hip joints. The term hip dysplasia means malformation of the hip and describes a developmental disease of the hip joints in young dogs of many different breeds. Unsound hip joints are a common problem in working and sporting breeds, and hip dysplasia is a serious problem in any dog that is to be trained for a demanding activity.
SIGNS: Signs of hip dysplasia cannot be detected in the newborn puppy, but may appear in the rapid growth period between four and nine months of age. Signs of the disease can vary widely from slight irregularities of gait to crippling hip disease. Improvement or even apparent disappearance of lameness can occur as the dog matures but arthritis of the hip joints is usually present in the older dog with dysplasia.
DIAGNOSIS: The best way to determine the condition of the hip joints of a dog is by good X-ray examination. Sedation or a short acting anaesthetic may be necessary to restrain the dog so that a diagnostic film can be taken.
TREATMENT: Your veterinarian may suggest rest and supportive care as a medical treatment during the acute phase of the disease. Surgical treatment for the relief of pain may be of value if discomfort persists. Moderate and regular exercise, control of excessive weight and anti - inflammatory drugs are helpful in the management of arthritis associated with hip dysplasia in the older dog.
GENETICS: Hip dysplasia is an inherited defect with a polygenetic mode of inheritance. The degree of inheritability is moderate in nature and the condition of the hip joints can be modified by environmental factors such as over nutrition and excessively rapid growth. As with any quantitative trait, hip joint conformation can range from good to bad with any all shades in between.
CONTROL: In as much as faulty hip joints are not readily observable, dogs intended for breeding should be x-rayed when mature to select for sound hips. Eighteen months of age is considered to be the minimum age for radiographic certification of desirable conformation with respect to canine hip dysplasia.
Ideally, dogs with hip dysplasia should not be used for breeding.
Multiple epiphysial dysplasia: most common osteochondro-dysplasia: a condition where many of the long bones develop abnormally due to changes in the growth plates. It is characterised by disturbance of normal ossification w/ in epiphysis. It is inherited as an autosome dominant trait with variable expressivity. This disorder is manifested as multiple areas of abnormal growth ossification of the epiphysis. It tends to be bilaterally symmetrical and to affect predominantly joints of the long bones. Resulting irregularities of joint surfaces often lead to degenerative arthritis, with significant disability by maturity. Some diminution in stature is present although not severe, but is often not apparent until later stages of puppyhood.
Breeding is inadvisable with animals diagnosed with multiple epiphysial dysplasia.
Muscular dystrophy: a congenital and often inherited form of generalised muscle dysfunction which causes signs such as poor growth, weakness, abnormal gait, difficulty eating and swallowing, and muscle atrophy. Affected animals have serious health problems and may die or be euthanized. Animals diagnosed with muscular dystrophy should not be used for breeding purposes.
Osteochondritis dissecans (OCD): a specific form of inflammation of the cartilage of certain joints which causes arthritis. (See Osteochondrosis below.)
Osteochondrosis: a group of developmental diseases resulting in abnormal formulation of joint cartilage. Commonly involves the shoulder, stifle, hock or elbow. Osteochondrosis manifests as a disturbance of the normal growth of bone underneath the cartilage of joints. It is a disease primarily of young, large boned, rapidly growing dogs, with both environmental and genetic factors believed to be involved in the development of the disease. In affected joints, the cartilage becomes thickened, and portions of the cartilage may die. Treatment may consist of limiting activity, analgesic agents, and possibly surgery to remove portions of loose cartilage or bone from the joint.
Short tail: a tail that is abnormally short for the breed in question.
DERMAL(1,3,4)
Colour mutant alopecia: a condition where certain colored areas of a dog's skin grows less or no fur.
This disease affects many animals with BLUE coats. It can also affect those with FAWN coats as well. Simply put it is hair loss, dandruff, and excessively dry skin. Dogs with blue or fawn coats must be maintained by proper diet and bathing when necessary . However, too much bathing can dry out the skin and must only be done
when absolutely necessary.
Demodicosis: a kind of skin disease (mange) caused by microscopic Demodex canis mites living within the skin layers and producing an immunodeficiency syndrome. This refers to infestation with species specific Demodex mites. It is uncommon in most domestic species with exception of the dog. Most animals (including human beings) have a resident population of Demodex mites that reside within hair follicles and/or sebaceous glands. Transmission from dam to offspring can occur during nursing. Canine demodicosis is more common in young dogs or immunocompromised older dogs, and occurs in localised or generalised forms.
Grossly, the localised form consists of one to several scaled, erythematous, alopecic macular foci on the face or forelimbs. Histologically, there is lymphoplasmacytic perifollicular inflammation, with hyperkeratosis, sebaceous adenitis, pigmentary incontinence, and intrafollicular mites. There may be secondary bacterial infection, rupture of hair follicles and resultant furunculosis.
Generalised demodicosis consist of larger coalescing patches of lesions that are grossly and histologically similar to the above.
Pemphigus foliaceous: another skin disease caused by autoimmune destruction of tissues; it is a component of the pemphigus/pemphigoid complex
This includes pemphigus foliaceus (gross, microscopic), pemphigus vulgaris (gross 1, gross 2, microscopic), pemphigus vegetans, pemphigus erythematosus and bullous pemphigoid. All have been reported in the dog. All except pemphigus vegetans and bullous pemphigoid in the cat. Pemphigus foliaceus has been reported in the horse(gross 1, gross 2). All the pemphigus diseases have in common the formation of antibody against proteins bound to phakoglobin, a component of both desmosomes and adherans junctions between epithelial cells. The binding of these antibodies causes breakdown of desmosomes, causing loss of cohesion between keratinocytes. This results in rounding up and separation (acantholysis), and vesicle formation. From a clinical standpoint, there will be vesicle or pustule formation. Due to thinness of canine and feline epidermis, vesicles or pustules are usually extremely transient, resulting the in the more common presentation of crusting. The loss of cohesion can be demonstrated by the Nikolsky test. This is done by putting lateral, shearing pressure on the skin. Erosions can be induced by this shearing force.
More specific diagnosis can be made by immunohistochemical staining for antibodies bound to tissue components. Because of the characteristic autoimmune reaction in these diseases, antibodies will usually be detected between keratinocytes.
Important and by far more common differential diagnoses include any cause of pustular to crusting lesions of the skin. Some of the more important are bacterial (Staphylococcal) or parasitic (demodectic) dermatitides.
In bullous pemphigoid, the antibody is directed against elements of the basement membrane (BP antigen). Deposition of antibody results in separation of the dermoepidermal junction (beneath the basal epithelium), and vesicle formation. Acantholytic cells are not found. Generally, these conditions present clinically as transient blister formation accompanied by widespread, often symmetric erosions, ulceration, crusting, scaling and depigmentation.
OTHER
Behavioral abnormalities: a whole range of abnormal behavior patterns, such as aggression, panic disorders, etc. The key to overcoming these is a proper and positive training regime.
REFERENCES