Common Symptoms
Congenital myasthenic syndrome (Jack Russell terrier type) is an inherited Neuromuscular Disease affecting dogs. Affected dogs typically present around 6-7 weeks of age with severe exercise-induced weakness leading to collapse. During episodes of weakness dogs will have decreased reflexes in all limbs and a short-strided gait that progressively worsens until they collapse. Weakness resolves after rest and dogs are clinically normal between episodes of weakness. Dogs develop resistance to treatments used for a similar, acquired form of the disease known as myasthenia gravis, and may be humanely euthanized within 3 months of age due to disease severity.
Breed-Specific Information for the Parson Russell Terrier
Parson Russell terrier is included as a breed susceptible to congenital myasthenic syndrome (Jack Russell terrier type) because of its close relatedness to the Jack Russell terrier breed which is known to develop this disease due to Mutation of the CHRNE gene. The frequency of the causal mutation in the general Parson Russell terrier population is unknown.
Testing Tips
Genetic testing of the CHRNE gene will reliably determine whether a Parson Russell terrier is a genetic Carrier of congenital myasthenic syndrome (Jack Russell terrier type). Congenital myasthenic syndrome (Jack Russell terrier type) is inherited in an Autosomal Recessive manner in dogs meaning that they must receive two copies of the mutated gene (one from each parent) to develop the disease. In general, carrier dogs do not have features of the disease but when bred with another carrier of the same Mutation, there is a risk of having affected pups. Each pup that is born to this pairing has a 25% chance of inheriting the disease and a 50% chance of inheriting one copy and being a carrier of the CHRNE gene mutation. Reliable genetic testing is important for determining breeding practices. In order to eliminate this mutation from breeding lines and to avoid the potential of producing affected pups, breeding of known carriers to each other is not recommended. Parson Russell terriers that are not carriers of the mutation have no increased risk of having affected pups.
There may be other causes of this condition in dogs and a normal result does not exclude a different mutation in this gene or any other gene that may result in a similar genetic disease or trait.
References
-
Rinz CJ, Lennon VA, James F, Thoreson JB, Tsai KL, Starr-Moss AN, Humphries HD, Guo LT, Palmer AC, Clark LA, Shelton GD. A CHRNE frameshift mutation causes congenital myasthenic syndrome in young Jack Russell Terriers. Neuromuscul Disord. 2015 Dec;25(12):921-7.
[PubMed: 26429099]
