Studying the genetics of how some traits are passed down in dogs is still a relatively new field. Understanding why one dog gets cancer and another doesn’t for example, is a frustratingly difficult problem to unravel, especially since we don’t even yet know why most people with cancer get the disease.
Veterinarians have long recognized that certain breeds of dogs seem to have specific problems more often than other breeds. Sometimes those problems are directly related to traits we can easily see by just looking at the dog’s body. Many times these traits turn out to be the exact reasons that certain breeds are so popular. For example, we love the English bulldog’s enormous head, but it’s genetically selecting for that trait (because people find it desirable) that has caused the vast majority of bulldog puppies to be born via caesarean section. Their heads are simply too large to come through the birth canal!
If you’re considering buying a purebred puppy, or even if you’re considering rescuing a purebred adult dog, it’s a good idea to be aware of the most commonly seen health problems that occur in purebreds, and even mixed breed dogs that are made up of those breeds.
Brachycephalic airway syndrome
People find stubby-nosed dogs adorable. But having this short head, which is known as brachycephalism, can create a number of health problems for the breeds that have it. Most of those problems have to do with the ability to breathe, which is clearly an enormously important bodily process. The syndrome is usually recognized to have three components.
The problem starts at the nose. Many of these dogs have what are called “stenotic nares”, which basically means that the openings of the nostrils are very small. This makes it difficult to draw in air through the nostrils, which can cause severe respiratory distress and the inability to adequately cool the body.
Another component of the syndrome is a long soft palate. Think of this area as the back of the roof of the mouth. The front part of the palate is bone covered by flesh, but further back in the mouth the bone ends. In brachycephalic breeds this flesh is often abnormally long, hanging down into the oral cavity and oftentimes over the airway, further complicating breathing.
The third component of the syndrome is a hypoplastic, or small, trachea. You can imagine why having a trachea of small diameter alone would make getting air into your lungs difficult, but combine all three of these anomalies and you’ve got real problems.
Stenotic nares and long soft palates can be corrected surgically. There’s nothing that can be done for a hypoplastic trachea, but fixing the other two problems will improve the dog’s quality of life significantly. Well-known brachycephalic breeds include bulldogs, Boston terriers, shih tzus, pugs, boxers and Pekingese.
Heart disease
Dogs sometimes get heart disease very late in life, but when very young dogs are affected it’s almost always due to an inherited condition. Dogs can have problems with specific valves in the heart either being improperly formed (cavalier king Charles spaniels, bull terriers) or from valves being too small (German shepherds, golden retrievers). Typically these dogs start showing problems as puppies, such as weakness and/or exercise intolerance. In many cases a heart murmur is heard at the first or second visit for routine vaccinations and deworming.
We still don’t have all the answers, but many times we can predict the possibility that a dog will pass along heart disease to its offspring, either by blood testing for specific genetic markers or detection of clinical problems. Conscientious breeders work to identify potential carriers of heart problems and remove those dogs from the breeding pool.
Cryptorchidism
In male puppies the testicles are still in the abdomen when they are born. Somewhere in the first month or two of life, they “drop”, which means they descend through the inguinal canal and into the scrotum. Cryptorchidism means that one or both of the testicles never made this journey, and is thus stuck somewhere in between.
Cryptorchidism is always inherited. It happens in purebred dogs about twice as much as it does in mixed breed dogs. It’s concerning because left in the abdomen, testicles are subjected to the higher temperatures there, and more prone to becoming cancerous. Cryptorchid males will almost always sire cryptorchid puppies, or puppies that carry the gene for it, if allowed to breed.
Orthopedic disease
Dogs are at risk for inheriting many orthopedic conditions. Luxating patellas are likely the most commonly inherited skeletal disease in dogs. They typically occur in toy and small breed dogs, but can occur in larger dogs too.
In this condition the groove in which the kneecap sits is not deep enough, and the kneecap tends to slide around to the right and the left, in and out of the joint. This is called “luxating”. The degree to which the animal is affected by this problem is determined by how much the kneecap moves around. A fair number of dogs are so significantly affected that they need surgery to stabilize the knee and prevent serious arthritis later.
Hip dysplasia is another common orthopedic disease that can be inherited, although other factors play a role as well. Large breed dogs are commonly affected, and mixed breeds can have hip dysplasia too. In hip dysplasia the “socket” of the hip joint, known as the acetabulum, is very shallow. It should have a nice “C” shape to it so that it holds the head of the femur, the “ball”, snugly in place. The shallow acetabulum allows the head of the femur to roam around in the joint, destroying the cartilage and ultimately leading to debilitating arthritis.
The website of the Orthopedic Foundation for Animals (www.offa.org) can help you research inherited conditions in purebred animals. The OFFA is an independent organization that uses accepted testing mechanisms to certify that breeding animals are free of certain inherited conditions.
Intervertebral disk disease
Dogs with long backs and short legs are called “chondrodystrophic” breeds. While dachshunds and Bassett hounds are adorable, their bizarre anatomy ties in with an increased risk for what’s called Hansen Type I disk disease.
For reasons we don’t yet understand, these breeds seem to have intervertebral disks that are weak and thin at the top. There’s an intervertebral disk between each and every pair of vertebrae in their long backs, and the weakness in them makes them prone to bulging and extruding upwards, where they exert extreme and sudden pressure on the spinal cord itself. The result is that the dog is acutely paralyzed, and usually surgery holds the only hope for restoring function.
Gastric Dilatation and Volvulus
Deep-chested breeds, like Dobermans, Great Danes, and standard Poodles are at risk for an extremely serious condition called gastric dilatation and volvulus, or GDV. These breeds (and again, this can happen in deep-chested mixed breed dogs too) are prone to a bizarre set of circumstances in which the stomach fills with a large amount of air – this is the gastric dilatation, or “bloat” part. The subsequent heaviness of the air-filled stomach causes it to flip on its axis, blocking the entrance and exit to the stomach and occluding the large blood vessels that supply it.
GDV is a life-threatening condition that leads to death if not treated. Because of this many veterinarians recommend a surgical procedure for deep-chested dogs in which the stomach is sewn to the body wall. This won’t prevent the bloating, but it will prevent the twisting.