Myasthenic syndrome in Jack / Parson Russell Terrier

Congenital myasthenic syndrome is an inherited disease that affects neuromuscular transmission. It is manifested by fatigable weakness of the skeletal muscles after exercise. The first symptoms can be already observed in puppies at the time of weaning, but the disease progresses rapidly, and most dogs die within 1 year of age.

In Jack Russell Terriers and Parson Russell Terriers, the disease is caused by mutation c.636_637insC in the CHRNE gene, which encodes the epsilon subunit of the acetylcholine receptor in the neuromuscular disc.

The mode of inheritance of the mutation is autosomal recessive. This means that only individuals who inherit the mutated gene from both parents will develop the disease. Carriers of the mutated gene are clinically healthy but pass the mutation on to their offspring. In the case of a mating between two heterozygous individuals, theoretically 25% of the offspring will be completely healthy, 50% of the offspring will be carriers and 25% of the offspring will inherit the mutated gene from both parents and will therefore be affected by the disease.

The genetic test can clearly reveal the genotype of the animal and is a useful tool for breeders to prevent unintentional breeding of affected puppies.

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Reference:

Rinz, C.J., Lennon, V.A., James, F., Thoreson, J.B., Tsai, K.L., Starr-Moss, A.N., Humphries, H.D., Guo, L.T., Palmer, A.C., Clark, L.A., Shelton, G.D. : A CHRNE frameshift mutation causes congenital myasthenic syndrome in young Jack Russell Terriers. Neuromuscul Disord 25:921-7, 2015. Pubmed reference: 26429099