WHAT IS NEBL3 (AG or GG gene)?
The ” NEBL3 or AG” gene in Cavalier King Charles Spaniels serves as a genetic marker within the NEBL gene, offering possible protection against early-onset Myxomatous Mitral Valve Disease (MMVD), a leading cause of death in the breed. Understanding this genetic variation can assist breeders in making informed decisions and help owners manage their pet’s health effectively.
Why is this important for the Cavalier breed.
Its early days and we wont really know for about 10 years the full impact on our lovely breed, BUT, it is looking very positive, This gene may help prevent the heart from enlarging due, NEBL3 does not work directly on the mitral valve but influences the integrity of the papillary muscle, which supports the valve. Google search NELB3
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Gene Expression:The NEBL3 gene provides instructions for making a protein called nebulette.Structural Support:The nebulette protein is important for the integrity of the papillary muscle, a crucial structure that supports the heart’s mitral valve.Preventing Cardiac Enlargement:In individuals with the wild-type NEBL3 variant, the nebulette protein maintains the papillary muscle’s health, preventing the heart from dilating in response to valve insufficiency, which is a key aspect of MMVD.MMVD Progression:When the papillary muscle degenerates, the valve leaflets are pulled apart, increasing the leak and worsening the condition. The NEBL3 variant helps to slow this process.
NEBL3 and MMVD in Dogs:
Genetic Testing: Genetic tests for the NEBL3 variant can identify dogs at lower risk for MMVD.
Breed-Specific: This research has primarily focused on CKCS and Dachshunds.
Breeding Strategy: Understanding the NEBL3 gene allows breeders to make informed decisions to potentially reduce the prevalence of early-onset MMVD in these breeds.
Key Takeaways:
- NEBL3 plays a role in maintaining the health of the heart’s support structures, not the valve itself.
- The wild-type NEBL3 variant is protective against early MMVD and helps to slow its progression.
- Genetic testing for NEBL3 can be a valuable tool for breeders in creating healthier Cavalier King Charles Spaniels and Dachshunds
What is a heart murmur?
A heart murmur is a type of abnormal sound that can be detected when listening to the heart with a stethoscope (a procedure called auscultation).
Normally, we hear two distinct sounds. Medically these are called S1 and S2 but most of us know them as lub and dub. Listening to a normal heart beating sounds like lub-dub … lub-dub … lub-dub.
The lub sound represents the closing of the top two valves (the mitral and tricuspid) and the dub sound represents the closing of the bottom valves (aortic and pulmonary). See below
A murmur is an extra sound, often heard between the lub and the dub. So we hear lub-whoosh-dub … lub-whoosh-dub … lub-whoosh-dub. Some murmurs are loud enough to drown out the other heart sounds so we only hear whoosh … whoosh … whoosh.
The murmur sound comes from turbulent blood flow. Before we look at the causes of turbulence, we need a quick refresher of heart anatomy and function.
This is a diagram of a human heart but it’s pretty much the same in dogs.
What causes a heart murmur?
The most common cause of a heart murmur (ie turbulent blood flow in the heart) is a valve problem. We have two main types of problem:
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a leaky valve – that allows back flow through it when it’s closed
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a stiff valve – that doesn’t open up properly and blood has to ‘squeeze’ through it
Other causes of turbulence include:
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a ‘hole in the heart’ (eg a patent ductus arteriosus, ventral septal defect)
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a narrowing of a chamber (eg when the heart muscle thickens due to hyperthyroid disease in cats)
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anaemia (ie too few red cells in the blood)
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a very rapid heart rate (and breathing rate) in an excited or anxious dog
All of these cause the blood to ‘churn’ rather than flow and we then hear a murmur – but note that not all of them are caused by heart disease. There’s nothing wrong with the heart in the bottom two examples.
We can get clues to the cause of a murmur from the dog’s age and breed and from where the murmur is the loudest, when it occurs (ie during systole or diastole) and how it sounds. For example, a murmur due to a patent ductus arteriosus is heard continuously in the left armpit and sounds like a sneaker in a washing machine.
By far, the most common cause of a murmur in dogs is a leaky mitral valve. These are the whooshy murmurs, loudest on the lower left side of the chest (and usually in older dogs).
What does the grade of the murmur mean?
If your dog has been diagnosed with a heart murmur, you’ve probably been told that it’s a certain grade (1 to 6).
This simply refers to how loud the murmur is – it doesn’t always relate to the severity of the disease causing the murmur.
A grade 1 murmur is very soft and can only be heard in a quiet room with careful listening. A grade 6 murmur is so loud that you really don’t need a stethoscope, you can hear/feel the vibrations through the chest. Note that these grades are subjective – what sounds like a 2 to one person may sound like a 3 to another.
How is the cause of the murmur diagnosed?
As mentioned, in many cases, looking at the dog and listening to the murmur tells us the most likely cause.
If we’re unsure of the cause or we need to work out if the murmur is problematic, we may need to do some testing. Depending on the situation, this could involve:
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a heart ultrasound (called an echocardiogram or echo) – this allows for evaluation of the valves and the chambers of the heart (we can do very basic echoes inhouse but refer to a specialist cardiologist for comprehensive scans)
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chest X-rays – these allow us to see the size and shape of the heart and assess the lungs (but we can’t see the valves)
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blood tests – these can help us look for other conditions that can affect the heart (eg anaemia, thyroid disease) and we can check for special factors that tell us if the heart is stretched
Not all heart murmurs require investigation.
What is the treatment for a heart murmur?
When treatment is indicated, it’s aimed at:
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the underlying disease (eg surgery to open up a stiff valve)
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the consequence of heart disease (eg diuretics for congestive heart failure)
The most common underlying cause (leaky mitral valve) does not have any curative treatment as valve replacement surgery is not really available for dogs as yet.
What is Myxomatous Mitral Valve Disease (MMVD)?
Myxomatous mitral valve disease (MMVD) is a progressive cardiac condition, most common in dogs (and seems effect CKCS especially), where the mitral valve degenerates, leading to its distortion and an inability to form a complete seal. This results in blood leaking backward into the left atrium during heart contractions, causing a heart murmur. Over time, MMVD can lead to left atrial dilation and congestive heart failure (CHF). Diagnosis involves a VET listening to the heart and giving the Murmur a grading usually between 1 to 5, confirmation typically involves an echocardiogram, and treatment focuses on managing the disease with medications and lifestyle changes, such as dietary considerations.
Important links to gain a deeper understanding of why this could be the best new discovery for Cavalier hearts.
OVERVIEW Of MMVD from Dog breeding Science
View the vido to
- The AG gene marker is found within the NEBL gene.
- It’s a protective genetic variant that influences a dog’s likelihood of developing MMVD.
- A dog’s genotype can be either AA, AG, or GG.
- AG or GG:These dogs are considered to have a protective genetic makeup against MMVD, meaning they are less likely to be diagnosed with the disease at a young age.
- AA:These dogs are more likely to develop MMVD early in life and require more careful monitoring.
- Breeders can use this DNA test to screen their adult dogs and make informed breeding decisions.
- For pet owners, understanding the genetic status of their Cavalier can help with early veterinary care and monitoring.
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