FADD gene pathogenic variants causing recurrent febrile infection‐related epilepsy syndrome: Case report and literature review

Abstract FIRES and NORSE are clinical presentations of disease processes that, to date, remain unexplained without an established etiology in many cases. Neuroinflammation is thought to have paramount importance in the genesis of these conditions. We hereby report the clinical, EEG, brain MRI, and genetic findings of a nuclear family with recurrent febrile‐related encephalopathy with refractory de novo Status Epilepticus. Whole‐exome sequencing (WES) revealed a homozygous p.C105W pathogenic variant of FADD gene (FAS‐associated protein with death domain, FADD), known to cause ultrarare forms of autosomal recessive immunodeficiency that could be associated with variable degrees of lymphoproliferation, cerebral atrophy, and cardiac abnormalities. The FADD‐related conditions disrupt FAS‐mediated apoptosis and can cause a clinical picture with the characteristics of FIRES. This observation is important because, on one hand, it increases the number of reported patients with FADD deficiency, showing that this disorder may present variable expressivity, and on the other hand, it demonstrates a genetic cause of FIRES involving a cell‐mediated inflammation regulatory pathway. This finding supports early treatment with immunomodulatory therapy and could represent a new avenue of research in the field of new onset refractory status epilepticus and related conditions.