Genetic or related disorders in Great Danes.
Dr. Carel Breytenbach (BVSc), Muldersdrift Animal Clinic, muld_vet@mweb.co.za, 011-7952025
There are around 45 recognised congenital and heritable disorders in Great Danes. Some of them much more common than others, some less important from a health perspective and other potentially life-threatening conditions that can be very debilitating for any Dane owner and breeders alike.
So how do we know if a puppy we want to acquire as a new life companion or one we are selecting to be used in an ethical breeding program has one of these disorders or not?
In this article I will try and highlight some of the more important conditions and give some guidance as to which ones we can easily test for and select against (like HD&ED), and which ones has a breed predisposition (like GDV) and is not necessarily genetically linked. Others again has a low heritable coefficient and cannot easily be selected against (like OCD).
Let’s first try and explain a bit more about the terminology……
What is a genetic disorder?
Most diseases are affected to some extent by both genes and the environment. A genetic disorder is one in which an abnormality in the genetic make-up (the genome) of the individual plays a significant role in causing the condition. Although some disorders occur because of spontaneous mutation and cannot be selected against, many other genetic disorders are inherited, and a lot can be done to select against them in an ethical breeding program. These conditions are seen quite often in dogs, mostly but not exclusively in purebreds. This causes situations that are often heart-breaking because the dog is generally a well-loved family member by the time the condition becomes apparent and has been diagnosed by a veterinarian.
The role of genes in disease
The role played by genes in disease is becoming better understood and more tests is becoming available every day, some of them unfortunately already available, especially in the overseas markets, but still not scientifically proved to be correct. Genetic factors are involved to a greater or lesser extent in congenital malformations (conditions with which an animal is born), metabolic disorders, disorders of immune function, disorders associated with aging, and cancer. These categories of disease have become relatively more important as infectious, parasitic, and nutritional diseases have become less common due to vaccination programmes and advancing knowledge about nutrition, treatments and diagnostic methods.
How to reduce inherited disorders
The frequency of inherited conditions can be reduced through good breeding practices. For this to occur, we need to know how the disease is inherited (the mode of inheritance), how to identify the condition as early as possible, and ways to recognize carriers of the disease who, except in the case of autosomal dominant traits, are not clinically affected. For many of the disorders that are believed to be inherited, the specific pattern of inheritance has not been established. Breeds that have an increased risk for a condition, relative to other dog breeds, are said to have a breed predisposition. Preferably, affected dogs and their close relatives should not be used in breeding programmes.
Now let’s discuss a few individual conditions:
How is GDV inherited?
It appears that conformation and size are what predispose a particular breed to this disorder, such that breeds with a deeper and narrower chest are most susceptible. Within such a breed, dogs with a higher thoracic depth/width ratio (i.e. the deepest, narrowest chests) are the most vulnerable to GDV. Genetic tests been done overseas are still questionable in my opinion.
Is OCD inherited?
OCD is a considered to be a common disease in large and rapidly growing breeds of dogs, with most affected breeds averaging over 30Kg. However, some medium breeds, such as the bull terrier, greyhound and border collie, also have a high incidence of this disease. Although the factors that cause OCD are not completely resolved, direct factors considered to be involved in the development of OCD are rapid growth and trauma to the joint. Indirect factors affecting rapid growth include nutrition, hormones, and genetic predisposition to rapid growth and large size. Indirect influences that may lead to increased trauma to the joint include conformation and behaviour, which are also influenced by heredity. Therefore, the genetic link for most types of OCD is considered to be indirect, that is, an inherited tendency and thus have a low heritable coefficient. Certain sites for OCD lesions, such as the elbow, appear to have a greater direct genetic contribution and a higher heritability than other sites, such as the shoulder. The most important contributing factor in OCD of the shoulder, the most common site, is thought to be trauma.
The overall increased incidence in males for this disease is thought to be due to the increased growth spurt in the male around the susceptible time period for OCD development. As well, it is tempting to speculate that behavioural factors common to males might also be involved in this increased susceptibility.
DCM or Dilated Cardiomyopathy.
Though it is easy to test for and diagnose a dog even with early signs of DCM, a dog can develop this condition at any stage of his life and a negative heart scan cannot clear that dog for the rest of his life or give any proof that he cannot still develop it or pass it on to his offspring.
Because this is a very debilitating disease with a definite death sentence irrespective of supportive treatment, it is still advisable to test all dogs every time before they are bred, because early DCM does not necessarily go accord with clinical symptoms at such an early stage.
So, let’s look at a more detailed list of some of the common or more important conditions
The disorders listed in the first 3 categories below are believed to have an inherited basis, or are known to have a predilection for this breed (‘breed predisposition’). This means the disorder occurs more commonly in this breed compared to other breeds, or to the general dog population. Common sense only suggests that these are inherited disorders, but for many disorders, the studies to determine the mode of inheritance or the frequency in the breed have not been carried out, or are inconclusive.
The disorders listed are ones for which there is a general consensus among those investigating in this field internationally, and among veterinary practitioners, that the condition is significant in this breed.
The last category lists conditions that have been reported sporadically, and may be inherited in this breed.
Most Important
These disorders are relatively common in this breed, and where possible, all efforts should be made to eradicate them in any breeding program. These disorders seriously affect the health of your pet and may require medical or surgical intervention and can cause acute death.
- Dilated cardiomyopathy
- Cervical vertebral instability (Wobbler syndrome)
- Hip dysplasia
- Elbow dysplasia
- Deafness (mostly linked to the “Double Merle” Danes)
- Microphthalmia & ocular dysgenesis
- Megaoesophagus
Other disorders which have an increased incidence in this breed
These disorders occur less commonly or are less devastating than those mentioned above.
- Subaortic stenosis
- Cataracts
- Demodicosis/ Demodectic mange
- Ectropion
- Entropion
- Glaucoma
- OCD (please see references below)
- Hypothyroidism (familial lymphocytic thyroiditis)
- Mitral valve dysplasia
- Persistent right aortic arch (vascular ring anomaly)
- Progressive retinal atrophy
- Tricuspid valve dysplasia
- Dental malocclusions (over or under shot jaw)
- zinc-responsive dermatosis
Disorders associated with conformation
These disorders are directly related to the conformation or standards for the breed. Although these conditions have in many cases become so common that they are accepted as normal for the breed, they can still cause serious physical problems and discomfort for the dog. One component of responsible breeding is to breed away from the extremes of conformation that cause these physical problems.
Other disorders which may be inherited in this breed
These disorders have been reported sporadically, and may be inherited in this breed.
Ok, let’s sum it all up;
It is my personal opinion that any Great Dane breeder should always do the following tests on both parents before the dogs are used for breeding:
Minimum requirements –
- HD & ED certification – This can easily be done with X-rays at your local vet that is then sent in to a panel of scrutineers, all specialist veterinary radiologists and they then issue a KUSA accepted certificate.
- Heart screening for DCM – This is again an easy procedure; Echocardiography that is basically a sonar done on the heart by a specialist veterinary ultra-sonographer.
- Eye examination, preferably to be done by one of the two specialist veterinary Ophthalmology clinics in Johannesburg or Cape town.
- Dental examination that can be done together with a general health check-up by your local vet, and any concerns can be referred for specialist opinion.
Further screening tests that should be done if there is a history of any specific condition in these lines –
- X-rays of the neck to screen for Wobbler syndrome and if suspected then an MRI scan
- X-rays of the shoulder, elbow and hock to screen for OCD lesions
- Barium swallow study to check for Megaoesophagus
- Thyroid blood tests
- Colour genetic tests nowadays almost a given, especially if you are breeding Harlequins
Links to References
Congenital and Heritable Disorders in Dogs
Humane Society Veterinary Medical Association
OCD
Canine Osteochondrois, Timothy M. Lenehan and Davis C. Van Sickle (76 references)
