Laryngeal Paralysis in the Miniature Bull Terrier

Background.

Laryngeal paralysis is a serious and sometimes deadly disease in some dog breeds that prevents proper opening of the larynx for breathing. It is a disease which is scientifically not well understood. Itleads to difficulties in breathing, especially during physical activity. In severe cases the dog may suffocate and die.

Symptoms you may see.

Dogs with laryngeal paralysis are noisy when breathing, in particularly, when panting.

As the disease progresses the dog may get tired more easily, develop a barkchangeand cough or gag when eating and drinking.

If severe upper airway obstruction occurs during strenuous exercise or when exercising in heat and humidityit can result in respiratory distress and collapse.

In some cases, dogs may present with difficulty swallowing or may regurgitate their food.

Signs may progress for months to years before becoming a clinical problem for the dog.

Scientific Progress is being made.

Due to the striking breed predisposition of Miniature Bull Terriers for a clinically homogenous early onset form of LP, German specialistshypothesised that a new genetic variant might be involved in causing LP in our breed.

In a study published 24th October 2019 in PLOS Genetics, a team of German specialists in canine head and neck surgery and geneticists from the University of Bern identified a mutation responsible for laryngeal paralysis in Miniature Bull Terriers, enabling the development of a genetic test for the disease.

To identify a genetic cause, researchers performed a genome-wide association study and analysed genome sequences of several hundred dogs to find mutations that occur in Miniature Bull Terriers with the disease. In the genome of affected dogs, they discovered an extra piece of DNA inserted into a particular gene (RAPGEF6 gene) that results in production of an incomplete, non-functional RAPGEF6 protein.

The researchers did not detect a perfect correlation between the mutation and the laryngeal paralysis, which suggests that other genetic and environmental factors also may contribute to the development of the disease. Additionally, this mutation only occurred in Miniature and standard Bull Terriers and thus cannot explain laryngeal paralysis in other dog breeds. However, the study identifies an important role for the gene RAPGEF6 in laryngeal nerve function.

Results and subsequent Pre – Breeding Testing

The results were not a prefect correlation. Not all dogs with the genotype LP/LP showed symptoms. However, complex risk calculations proved that these dogs do have an elevated risk of developing LP symptoms in the future. In addition some dogs with the genotype N/LP (carriers) did present with symptoms.

If as responsible breeders we wish to minimise and hopefully eliminate this condition from our breed the following guidelines should be adopted.

Dogs should be tested.

Genetic testing is now available and offered by Laboklin. The test requires a buccal (cheek or mouth ) swab and results can be obtained in around 2 weeks. Cost is £ 48.00 (including VAT).*

  • Dogs with genotype N/N are clear dogs.
  • Dogs with genotype N/LP are carriers. NOTE: Some of these dogs may develop LP symptoms. There is a 50% chance of passing the RAPGEF6 gene to their offspring.If two carriers are mated there is a 25% risk for each offspring to have an elevated risk of developing LP symptoms. Carriers should only be mated with clear dogs so that no puppies with elevated risk will be born.
  • Dogs with genotype LP/LP have an elevated risk of developing LP symptoms in the early years of their life and should not be used for breeding.

Treatment for dogs showing symptoms.

Treatment options can vary widely depending on the severity of signs and quality of life. Dogs that are not severely affected may be managed without a surgical intervention.

Management involves moderation in exercise, weight loss and possibly anti-inflammatory medications to reduce laryngeal swelling. Walking on harnesses and not collars around the throat.

Larynx paralysis may require surgery to relieve the difficulties in breathing.

Dogs that have severe difficulty breathing may be candidates for surgery. The most common performed procedure is a “laryngeal tie back” where one or both sides of the larynx is sutured into a permanently open position to relieve upper airway obstruction.

Tie back surgical procedures carry the risk of leaving the airway unprotected and increase the risk for aspiration pneumonia.

As a last resort, a tracheostomy can be performed. GNOSIS

Prognosis for improvement of clinical signs and quality of life is generally good. Unilateral (one sided) laryngeal tie back surgery usually results in less respiratory distress, less respiratory noise, and improved exercise tolerance, but leaves dogs at risk for developing aspiration pneumonia.

Some dogs with a more degenerative version of the disease can unfortunately progress to develop additional neurologic signs around one year following diagnosis, for these dogsthe prognosis is not as good.

 

(Correct at the time of writing (April 2020)

 

As many of you will have seen there has been significant debate about the reliability of the current LP test from Laboklin.
We have consulted with the Kennel Club for their guidance. Their geneticist has given us the following advice.
“This is not a definitive test; the original research says that homozygotes (‘affected’) have 10-17x the risk of this than other dogs (and that there is no statistically significant increased risk to heterozygotes/’carriers’). So perfectly possible to get an ‘affected’ dog that never gets the condition. It depends what the prevalence is in the wider population. If 5%, then a 10-17-fold increase gives a risk of 50-85% risk; if it is 1% (still quite high), then there is an 83-90% chance that the ‘affected’ dog won’t get it. And these risk factors depend on the population the research sample was taken from.
This is a risk-based test and not a pure single gene mutation test and therefore is of limited value. Risk based tests tend to be more help where a problem is very widespread.”
We will be continuing this conversation with the Kennel Club, as we believe further clarity on the use of this test would be helpful.
As a club we are always looking to improve the health of our breed and generally support testing, where it is proven to be reliable (such as PLL testing) and are prepared to mandate them as part of member’s breeding programmes.
Given the outcomes of the research and the reliability of the results of the current LP test we would like to make clear our current guidance. You may wish to undertake the testwith your dog as a means of obtaining some information.Blood tests currently appear more reliable than swab testing, however, any result may not be 100% conclusive and therefore not proven to establish the dog’s current status for the condition.
Given the reliability challenges of the test, the committee feels it is inappropriate to mandate the current LP test at this time and leaves the choice of using the Laboklin LP test for members to decide.
Mandy Bennett
Dr Mandy Bennett
Breed Health Co-ordinator
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