IFNA1 and herpes simplex encephalitis: Further notable phenotypic clues to a monogenic deficiency, in addition to HSE recurrence, include other recurrent viral diseases and severe reactions to vaccines.132 Overall, albeit uncommon, a monogenic defect in TLR3- and IFN-pathways should be suspected, primarily in children, especially with relapsing forebrain HSE secondary to viral reactivation, whereas DBR1 deficiencies should be sought in such cases of brainstem HSE.128,133