Truncating RELA variants drive autoinflammation and autoimmunity by impairing the negative feedback control of NF-κB.

The NF-κB signaling pathway coordinates inflammation, cell survival, and proliferation, while restraining excessive cell death to maintain immune homeostasis. Truncating mutations in RELA, encoding the NF-κB subunit p65, have been linked to autoinflammation and autoimmunity, but the underlying mechanisms remain incompletely defined. We investigated 6 patients from 5 unrelated families carrying heterozygous truncating RELA variants. Despite reduced p65 expression, patients exhibited a broad spectrum of inflammatory manifestations alongside elevated baseline and stimulus-induced proinflammatory cytokines. Functional analyses in patient-derived cells and mutant RELA-KI models showed that upstream NF-κB signaling was intact, but induction of inhibitory regulators such as IκBα and A20 was impaired. This defective feedback control shifted immune homeostasis toward amplified inflammatory responses that depended on the residual activity of the remaining functional RELA allele. Single-cell transcriptomics revealed distinct cell type-specific consequences: monocytes displayed constitutive type I IFN and NF-κB activation, B cells retained partial compensatory signaling, and T and NK cells exhibited transcriptional signatures of cell death pathways. Patient fibroblasts and mutant RELA-KI cells further confirmed enhanced TNF-induced inflammatory gene expression and hypersensitivity to apoptosis and necroptosis. These findings establish RELA haploinsufficiency as a cause of systemic immune dysregulation and link defective NF-κB feedback control to unchecked inflammation and inflammatory cell death.