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. It leads 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 bark change and cough or gag when eating and drinking. If severe
upper airway obstruction occurs during strenuous exercise or when exercising
in heat and humidity it 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.

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

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 dogs the prognosis is not as good.


Scientific Investigation.
Due to the striking breed predisposition of Miniature Bull Terriers for a
clinically homogenous early onset form of LP, German specialists
hypothesised 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.

However the researchers did not detect a perfect correlation between the
mutation and the laryngeal paralysis. Not all dogs with the genotype LP/LP
showed symptoms. However, complex risk calculations suggested that these
dogs could 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.


On the back of this research a genetic test has been made available 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).*

Due to the lack of perfect correlation between the mutation of the genome and
laryngeal paralysis the results of this test have proved largely inconclusive.
Empirical evidence from breeders and owners support the findings from the
research that some dogs tested as LP/LP “affected dog” have had no
symptoms and some dogs tested as carriers N/LP have presented with
symptoms.

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.”

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 we 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 test with 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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