|Why it’s Important for Pet Owners to Understand Genetic Testing
Cynthia O’Connor, DVM, DACT
Animal Reproduction Specialist
Slade Veterinary Hospital
This is an exciting time with amazing advances in veterinary medicine. The area of molecular genetics
has become one of the hottest areas of research bringing the development of genetic testing to dog
breeders. So why as a pet owner is this information important? Many pet owners are looking for a
happy, healthy pet to add to their family. Because they are not interested in breeding, many mistakenly
feel that they do not need to learn about genetic testing. Many of these people also fall into the trap of
impulse buying, by purchasing a dog in a pet store or via an internet puppy broker. Many impulse
purchases lack research into the health and temperament of the pedigree and these new owners can
only hope that the dice will roll in their favor with a happy, healthy pet. Genetic testing offers the
opportunity for many people to become more informed consumers. After all, would you consider
buying a car, sight unseen, with no history? Then, why would you not put in the same, if not more
effort, into investigating a new addition to your family that you will trust to sleep in your child’s bed?
To understand the use of genetic testing and their use for breeders and pet owners, we first need to
remember some basics about genetics. The term hereditary or genetic is used to describe a disease
caused by a DNA mutation that can be passed from parent to offspring. The term congenital is used to
describe a disease that is present at birth. It is important to remember that a congenital disease can be
genetic; however, not all congenital diseases are genetic. In fact, toxins, infections, and other
environmental factors can cause congenital diseases. It is also important to remember that not all
genetic diseases are identifiable at birth. A good example of this is progressive retinal atrophy (PRA) in
Portuguese Water Dogs (PWDs). Dogs affected with PRA generally do not show signs of blindness
until much later in life.
Once a disease is recognized as genetic, knowing how it is passed from generation to generation is
the next step in preventing and managing genetic diseases. There are several inheritance patterns
recognized in dogs including autosomal recessive, autosomal dominant, X-linked recessive, X-linked
dominant, and complex (polygenetic) disease. Recessive diseases account for a majority of the
diseases for which there is a known inheritance pattern and for which a genetic defect has been
identified. However, with continued advances in molecular biology and technology, this will soon be
true for complex (polygenetic) disorders as well.
We are probably most familiar with autosomal recessive traits. An example of an autosomal recessive
trait in Portuguese Water Dogs is storage disease (GM-1 gangliosidosis). With an autosomal recessive
trait, PWDs that have two copies of the normal gene are referred to as non-carriers or normal for that
particular trait. PWDs that carry one affected gene and one normal gene are referred to as carriers and
they do not show any signs of the disease. However, PWDs that are carriers may pass the affected
gene onto their puppies. Puppies that receive two affected genes, one from each carrier parent, will
develop the disease. These are important points to keep in mind for breeders as well as pet owners.
The goal of a breeder is to create healthy puppies while maintaining breed genetic diversity. Breeders
can utilize tests such as this to prevent producing an affected puppy, while still utilizing the genes of
exceptional carrier and in some instances, affected animals. It is important for pet owners to
understand that for autosomal recessive diseases such as this example in PWDs, a carrier dog is a
very healthy pet. This does not always hold true for other modes of inheritance, so when evaluating a
disease and the use of the genetic test, it is important to understand how the disease is inherited.
Health screening tests come in several varieties and vary on what they are able to identify, therefore
how they can be used in managing genetic disease. Some tests measure the phenotype, or what can
be seen in the animal. This may not directly relate to the genotype, or the genes regulating the disease.
Eye examinations by veterinary ophthalmologists for C.E.R.F (Canine Eye Registration Foundation)
certification and x-rays of hips for certification free of hip dysplasia by the Orthopedic Foundation for
Animals (O.F.A.) are examples of health screening tests of the phenotype of the dog. Most tests of the
phenotype only identify affected individuals, and not carriers. Phenotypic tests such as these are
utilized for health screening when the disease causing gene(s) is not yet known.
Direct gene tests are a direct measurement of the genotype. These detect the exact DNA defect or
mutation that is the cause of the disease. Results are often given as Normal, Carrier, or Affected. These
can be run at any age, regardless of the age of onset of the disorder. With tests for the genotype,
breeders can identify affected, carrier, and genetically normal animals. Most tests of the genotype are
for genes that are the sole and direct cause of a disease or condition. Examples of direct gene
mutation based tests such as these available for PWDs include GM-1 testing by NYU, prcd-PRA testing
by OptiGen, and juvenile dilated cardiomyopathy testing by UPENN.
The second type of genetic test is the linked marker test. Markers are segments of DNA that have an
identifiable physical location on a chromosome whose inheritance can be followed. A marker can be a
gene or it can be some section of DNA with no known function. Because DNA segments that lie near
each other on a chromosome tend to be inherited together, markers are often used as indirect ways of
tracking the inheritance pattern of a gene that has not yet been identified, but whose approximate
location is known. The results of these tests are often given as a pattern such as A, B, or C. The closer
the marker is to the disease causing gene, the less chance of a false positive or false negative with this
test. Linked marker tests are utilized when the direct gene mutation has not yet been identified.
A newer and more complicated application of direct gene tests allows for breeders to identify dogs that
carry "susceptibility genes" for certain diseases that are inherited in a more complex manner. This
type of direct gene test gives a risk for susceptibility to a disease based on the gene(s) of that
individual. Some of these susceptibility genes are necessary for the animal to be affected, though
other yet undiscovered genetic or environmental factors are also necessary, making this more
complex. Examples of genetic tests for susceptibility of disease are the tests for degenerative
myelopathy and juvenile renal dysplasia in several dog breeds. Other susceptibility genes are found to
occur at a greater frequency in affected animals, but are not present in all affected animals. An example
of this is the susceptibility gene for perianal fistula/anal furunculosis in German Shepherd Dogs.
The obvious advantage of genetic testing is the ability to immediately reduce puppy loss from
devastating diseases such as juvenile dilated cardiomyopathy in PWDs. Genetic testing allows
breeders, based on careful breeding practices, to prevent the production of an affected puppy and a
gradual selection away from this disease over several generations. There is nothing more devastating
to a pet owner than taking home a beautiful new PWD puppy only to have this puppy die suddenly
from this disease at such a young age. The emotional toll that this tragedy takes on the entire family as
well as the breeder is immense. With genetic based tests like this, breeders can identify healthy carrier
animals so that they can make careful breeding decisions in order to avoid tragedies such as this for
pet owners. Pet owners, in turn, can use these tests to help find breeders who are working to identify
and prevent diseases like this in their dogs.
Unfortunately, breeders can not look into a crystal ball and predict that a puppy they produce will
never get sick. However, an educated breeder can discuss with a new puppy buyer the most common
inherited diseases in their breed and their line. A buyer should be concerned when during a
discussion like this, a breeder states that they have no health concerns in their dogs and so have no
need to perform genetic testing. This should hint to the buyer that the breeder is either not very
forthcoming with health information, or does not know about the health history of their lines. A puppy
buyer, in turn, needs to understand the basics of these diseases and how they are inherited. For a
puppy buyer, it is important to remember that for a simple autosomal recessive disease, such as
juvenile dilated cardiomyopathy in PWDs, a carrier of the disease is a perfectly healthy pet. Buyers
also need to understand that for a disease that is inherited in this way, a breeder who breeds a carrier
to a normal dog will not produce the disease and may be making this decision to help preserve the
long term genetic health of their line and the breed as a whole. In fact, it has been shown that by
quickly eliminating animals that are carriers or affected by a genetic disease, the genetic diversity of
the breed is reduced and the incidence of other diseases is increased. Breeders utilize genetic tests as
one factor in making well informed breeding decisions and puppy buyers can also utilize them to
become well educated consumers in their effort to find a healthy new addition to their family.
|Click on the picture above for
health information provided by
the Portuguese Water Dog Club
of America (PWDCA).
|Click on the picture above for
health testing recommendations
|Querida Portuguese Water Dogs, LLC
|* Allergy & Skin
* Eyes Diseases
1. X-ray evaluation of
hips to certify free from
hip dysplasia (OFA).
Please note that while
the PWDCA does not yet
endorse PennHip, this is
an excellent alternative
hip dysplasia evaluation.
2. Eye examination by a
yearly until 10 years of age
(CERF or OFA ECR).
3. OptiGen Progressive
Retinal Atrophy (PRA) genetic
test of both parents with one
parent tested non-carrier.
4. One parent genetically
tested non-carrier for
5. One parent genetically
tested non-carrier for juvenile
|PWD Health Conditions
Click below for link:
|Click on the picture above for
PennHip information for hip