Consistent with case reports of tonic-clonic seizures occurring during mefloquine chemoprophylaxis among those with family histories of epilepsy [7], out of an abundance of caution and based on biological plausibility, consideration should be given to a contraindication to mefloquine use among those with EPM1 mutation; or absent formal genetic diagnosis, among those with a personal or family history of seizure, myoclonus, ataxia, or degenerative neurologic disorder consistent with EPM1. The gene discussed is CSTB; the disease is cerebellar ataxia.