Breeds Affected: Rhodesian Ridgeback
Samples Accepted: Blood, Buccal Swabs
Disease Information: JME is a form of epilepsy characterized by sudden, electric shock-like muscle spasms or jerks. The spasms often take place when a dog is resting or beginning to sleep, and may also be triggered by sudden exposure to bright light. Most dogs have seizures daily, and some dogs may have up to 150 short seizures per day. Although normally diagnosed by 6 months of age, pups have been diagnosed as early as 6 weeks or as old as 18 months. Up to 15% of Rhodesian Ridgebacks tested are carriers for the gene mutation responsible for JME.
Inheritance Information: Juvenile Myoclonic Epilepsy is autosomal recessive, meaning that animals with two copies of this allele will be affected. Animals with one copy of the gene will be clinically-normal carriers.
The possible genotypes are:
N/N The dog is normal, and cannot produce affected offspring.
N/jme The dog is a carrier, and can pass the allele on to approximately 50% of any offspring. If bred to another N/jme carrier, approximately 25% of the offspring will be normal, 50% will be carriers, and 25% will be affected.
jme/jme The dog is affected, and if bred to a normal animal, 100% of the offspring will be carriers. If bred to an N/jme carrier, 50% of the offspring will be carriers and 50% will be affected.
– Carriers may be bred to normal animals (N/jme x N/N) without any risk of producing affected offspring. The offspring should be tested before breeding to determine if they are carriers or normal.
– Breeding two carriers (N/jme x N/jme) is not recommended due to the possibility of 25% of the offspring being affected.
– Affected animals (jme/jme) should not be used for breeding.
Test Information: This mutation test identifies a 4 base pair deletion in the exon 2 of the DIRAS1 gene.
Wielaender, F., Sarviaho, R., James, F., Hytönen, M.K., Cortez, M.A., Kluger, G., Koskinen, L.L., Arumilli, M., Kornberg, M., Bathen-Noethen, A., Tipold, A., Rentmeister, K., Bhatti, S.F., Hülsmeyer, V., Boettcher, I.C., Tästensen, C., Flegel, T., Dietschi, E., Leeb, T., Matiasek, K., Fischer, A., Lohi, H. : Generalized myoclonic epilepsy with photosensitivity in juvenile dogs caused by a defective DIRAS family GTPase 1. Proc Natl Acad Sci U S A :114(10), 2017. Pubmed reference: 28223533. Doi:10.1073/pnas.1614478114.
To see examples of how JME seizures can look, Wielaender et al. (2017) have made videos available on the PNAS website. (CAG is not responsible for the content of linked sites).
Further information is available at the Online Mendelian Inheritance in Animals website.