Understanding genetic disorders

Incidences of genetic disorders can be reduced. Here are useful insights to reduce disorders practice.
Dr Onkar Pawaskar
Majority of diseases in dogs are influenced due to genes and/or environment. Genetic disorders involve the abnormality of a genome of the individual seen as in congenital malformations, immune or metabolic disorders and also cancer. Although complete prevention is difficult, the frequency of genetic disorders can be reduced by good breeding practices. For this, we basically need to know which diseases are inherited, how to identify the condition as early as possible and ways to find out carriers of these conditions.
So far, over 500 genetic diseases have been identified in purebred dogs, and over 100 in mixed breeds. They can affect conformation and temperament of your pet.
 
Purebred vs mixed breeds
Purebred dogs are generally more susceptible to inherited disorders than mixed breed ones because of their limited gene pool. Other health problems among purebreds are the product of both inbreeding and bad genetic luck.
Here are a few commonly found breeds in India and the genetic/inherited disorders commonly seen.
 
Labrador Retriever
Hip dysplasia: Loose fit between the ball and socket joint (femur and pelvis) mainly due to polygenic factors. Further causes that can make this worse are over-weight, fast growth rate and high calorie diet.
Diabetes mellitus: This is basically a disruption in body’s ability to use simple sugars. There is a genetic predisposition in some dogs to the destruction by the immune system of the insulin producing cells.
 
Atopy: Dogs with this condition become sensitised to allergens in the environment which is seen in form of excessive itching.
 
Pug
Dry eye (keratoconjunctivitis): Caused generally due to abnormal tear production. Deficiency of lacrimal glands to produce the watery secretions or tears due to predisposed genetic conditions is the main cause.
Fold dermatitis (pyoderma): Inflamation of the skin at areas of excessive wrinkling like tail, lip and facial folds due to wrinkling trait by mainly autosomal reasons.
 
Great Dane
Dilated Cardiomyopathy: Disease of the heart muscle tissue which is transmitted genetically from parent to child as found out in certain giant breeds.
This is very difficult to diagnose and is mostly untreated due to the same reason until it reaches last stage.
 
Gastric dilatation (Volvulus): Here the stomach gets distended with air and then twists on itself. Generally found in breeds with deep and narrow chest who are more often predisposed, it is one of the rare conditions wherein the pet can go from healthy to critical within a few hours with fatality found in 30 percent incidences.
 
Siberian Husky
Corneal dystrophy: An inherited abnormality resulting in painful chronic ulcers mainly due to autosomal recessive trait.
 
Beagle
Glaucoma: Blindness due to increased fluid pressure in the eye. Inherited open angles glaucoma is an autosomal dominant trait generally found in this breed.
 
Neurological and behavioural problems…
Neurological and behavioural problems affect many pure breeds. Bull Terriers, for example, often compulsively chase their tails. Pugs are predisposed to Pug Dog encephalitis, a fatal brain disease. Scottish Terriers are affected by Scottie Cramp, a disorder that causes the dogs to lose muscle control when they get excited. German Shepherds may inherit degenerative myelopathy, a crippling spinal cord disease that causes weakness and eventually paralysis. Basset Hounds are prone to an inherited abnormality which affects the ability of the platelets in the blood to clump together after an injury. The blood doesn’t clot properly, leading to haemorrhage and bruising.
 
Immune diseases…
A number of inherited diseases, compromising the immune system have been noted in dogs, including primary severe combined immunodeficiency (a dog version of the ‘bubble boy’ disease) among Basset Hounds, Cardigan Welsh Corgis, and Dachshunds. Addison’s Disease, an autoimmune disease that affects the hormone-producing adrenal glands, occurs more frequently among several particular breeds, including the Bearded Collie and Standard Poodles. Diabetes mellitus, an autoimmune disorder affecting the body’s response to sugars, shows up more frequently among Samoyeds and Australian Terrier dogs.
 
Skin problems…
Dog breeds prone to atopic dermatitis include Dalmatians, Vizslas, and several Terriers, such as the Boston Terrier, Bull Terrier and West Highland White Terrier.
The numerous skin folds of a Chinese Shar-Pei, so valued by some breeders, can become breeding grounds for staphylococcus and other bacteria, which cause frequent skin infections. Also, excess wrinkles of skin on the face can rub on the eye, causing lesions and, potentially, blindness.
 
Tips for preventing genetic disorders…

• Since genetic diseases are passed on to the next generation by parents who contribute to the causative factor with their own genes, the elimination can happen successfully by selective breeding.
• How to identify the diseases and causative factors is the first step in implementing the selective breeding programmes.
• When not to breed is also a very important decision which needs to be taken.
• Educating the masses or mainly the breeders about this problem is another important step.
• Breeders should only breed those dogs which will minimise the unwanted traits.
• One important factor is that future pet parents should be made aware of genetic disorders and  that they should ask breeders whether the dogs they breed have been selected accordingly or not.
• Veterinarians play a vital role in guiding the breeders, pet parents and everybody concerned with this activity.
• DNA-based tests should be made compulsory as part of breeding programmes.

(Dr Onkar Pawaskar runs Pet Clinic at Thane (W), Mumbai).