Genetic variants associated with rare seizures triggered in some children who are administered the measles, mumps, and rubella (MMR) vaccination are reported in a study published online this week in Nature Genetics. The results represent an important first step toward understanding what causes these seizures in children of European ancestry who receive MMR vaccination.
Fever is a common reaction to vaccines created from live viruses that have been altered to be much less virulent, such as the MMR vaccine. In rare cases these vaccines can lead to fever-related seizures, known as febrile seizures, which are generally 1-2 minutes long and currently are not believed to pose long-term neurological risks. In the case of the MMR vaccine, seizures occur in the second week after vaccination in a small proportion of young children. The reason why vaccine-induced fever can lead to seizures is unknown.
Bjarke Feenstra and colleagues compared genetic variants between approximately 1300 children who experienced MMR-induced febrile seizures, 2000 children with febrile seizures unrelated to the MMR vaccine and 5800 children with no history of seizures. They identified variants in two genes that associated specifically with MMR-related febrile seizures. The two implicated genes, IFI44L and CD46, are both involved in the innate immune response, which is responsible for the initial immune response to infection. IFI44L was previously shown to increase its expression after measles infection, and CD46 was previously linked to the immune response to the MMR vaccine.