Patients with Dravet syndrome (DS), tuberous sclerosis complex (TSC), or Rett syndrome/MECP2 duplication syndrome may have a satisfactory response to VNS, but it is unclear whether patients with rare variants of epilepsy-related genes can benefit from the treatment. This evidence concerns the gene MECP2 and encephalopathy, progressive, early-onset, with brain edema and/or leukoencephalopathy.