Searching for the cause of an inherited heart defect in Labrador retrievers.
Labrador retrievers are known for their loving, big-hearted personalities. But what happens if their literal heart has a congenital defect? And how can Labrador breeders choose mating pairs to decrease the chance of passing this heart defect along to future generations? The Labrador Retriever Club, Inc., the AKC Canine Health Foundation (CHF), and researchers at North Carolina State University (NCSU) have been working together to answer these questions for the condition known as tricuspid valve dysplasia (TVD).
What is TVD?
Tricuspid valve dysplasia (TVD) is the term used to describe a congenital heart defect involving malformation of the tricuspid valve. It can be seen in several dog breeds and mixed breeds, but is more commonly seen in Labrador retrievers, Irish setters, Great Danes, and German shepherd dogs.
The heart is made of four chambers; and blood flow is directed through the heart, lungs, and body via one-way valves. The tricuspid valve is one of these valves and sits between the right atrium and right ventricle. If it is malformed, blood can flow backward (known as regurgitation), preventing the normal circulation of blood throughout the body. The heart must work harder to compensate for this regurgitation, but eventually the right heart chambers become enlarged and adequate blood flow cannot be maintained. Right-sided congestive heart failure results and fluid accumulates in the abdomen and/or chest cavities.
Clinical disease in affected dogs ranges from mild valve malformation with little impact on the dog’s health to significant valve malformation resulting in severe regurgitation and eventual congestive heart failure. TVD may be suspected when the veterinarian hears a heart murmur while examining your Labrador. Definitive diagnosis requires an ultrasound of the heart (known as an echocardiogram or echo) to visualize the tricuspid valve, and to check for any other heart defects and their impact on heart size and function.
There is no readily available treatment that can alter or reshape the malformed heart valve. Therefore, medications are used to manage the resulting congestive heart failure and maintain a good quality of life for as long as possible.
Researcher Spotlight
Kathryn Meurs, DVM, PhD Diplomate ACVIM (Cardiology) is a board-certified veterinary cardiologist. She is an Interim Dean, Professor, and Associate Dean for Research and Graduate Studies at North Carolina State University College of Veterinary Medicine. In addition to her clinical duties, Dr. Meurs’ research focuses on the genetics of cardiovascular disease in animals.
What causes TVD?
Pedigree analysis and early genetic research provided evidence that TVD is an inherited disorder in Labrador retrievers – meaning that disease is caused by one or more specific genetic mutations in this breed. Dr. Kate Meurs and her team at NCSU set out to identify these mutation(s).
“Tricuspid valve dysplasia is definitely an inherited condition in the Labrador retriever,” Dr. Meurs says. “Because the heritability of this condition is so high in this breed, we thought there would be a single genetic mutation responsible for it. But that is not the case, and it appears that there could be more than one mutation causing this condition in the Labrador.”
By comparing the genetic sequences of affected and unaffected dogs, the research team found one mutation that is strongly associated with and likely the cause of TVD in Labs. However, not all affected dogs have the mutation; additionally, the mutation was found in some unaffected dogs. These results show that one genetic mutation is not the sole cause of TVD in Labrador retrievers. Additional genetic mutations and/or environmental factors must be at play.
A Complicated Puzzle
Since the genetic mutation identified by Dr. Meurs and her team is so influential in causing TVD in Labrador retrievers, it’s a critical piece of information to help decrease the incidence of this condition.
“The Labrador Retriever Club is very interested in developing some sort of screening test for TVD,” says Dr. Fran Smith, veterinarian, breeder, and vice president and health chair of the Labrador Retriever Club, Inc. “While TVD is not a common disease in Labradors, it can be devastating when your dog is affected by it.”
Dr. Meurs echoes this concern. “Studying the genetics that underly TVD in Labradors is important because some dogs can have a severe heart defect and die of heart failure even within the first year of life,” she states.
However, it’s important to know that TVD in Labrador retrievers is caused by more than a single genetic mutation. Breeders, owners, and veterinary professionals must keep in mind that other factors such as additional mutations, diet, lifestyle, and more can impact disease development.
“Genetics is complex,” Dr. Meurs says. “At this time, there is no good test to determine which mating pairs will result in puppies affected by TVD. The defect can skip generations. Even breeders who echo both parents and do everything right can still produce affected puppies.”
Additional study is needed to fully understand the genetic mutations that cause TVD in Labrador retrievers. Dr. Meurs and her team continue to search through the data to see if they can find additional mutations that influence disease development. The work is challenging, but worthwhile.
What’s a Lab Lover to Do?
If your Labrador has a heart murmur, schedule an echocardiogram with a board-certified veterinary cardiologist to get a definitive diagnosis of its cause. Work with your veterinary team to monitor and manage any signs of heart disease. Labrador retrievers with TVD should not be bred. Before breeding your Labrador or purchasing a puppy, learn about health concerns and clearances recommended by the Labrador Retriever Club, Inc. (www.thelabradorclub.com/health-issues).
It’s a complicated puzzle when you consider all the things that influence the health of your dog. Thanks to dedicated breed clubs, owners, and researchers, and the research funded through CHF, Labrador retriever lovers can take heart knowing that our collaborative efforts will help improve the health of these beloved companions.
About CHF
The AKC Canine Health Foundation (CHF) is a nonprofit organization dedicated to advancing the health of all dogs and their owners. Since its founding in 1995, CHF and its donors have invested more than $63.5 million in the highest quality canine health research grants and educational grants. The Foundation also shares information on the discoveries that help prevent, treat and cure canine diseases. CHF meets and exceeds industry standards for fiscal responsibility, as demonstrated by their highest four-star Charity Navigator rating and GuideStar Platinum Seal of Transparency. Learn more at www.akcchf.org.
