Transcriptional responses to TNF-alpha in germline A20 haploinsufficiency

Early-onset complex autoimmunity can arise from monogenic activating mutations in inflammatory signalling pathways or loss of function mutations of immunoregulatory molecules. We sought to define the molecular basis of severe early-onset autoimmunity, characterised by autoimmune diabetes, cytopenias, hepatitis, enteropathy and interstitial lung disease, in a child without pathogenic variants in STAT3 and FOXP3. We employed whole exome sequencing, together with in vitro assays of tumor necrosis factor-alpha (TNF-α) signalling and response, including RNA sequencing, in patient fibroblasts. We identified a novel de novo heterozygous variant in TNFAIP3, which encodes A20 - a key negative regulator of the NF-κB transcriptional induction pathway. The p.V489Afs*7 variant reduced A20 protein expression and resulted in hyperresponsiveness of TNF-α signal transduction. This was accompanied by significant enhancement of TNF-α induced NF-κB target gene expression. There was an excellent clinical response to matched unrelated haematopoietic stem cell transplantation (HSCT), with resolution of all pathological features except diabetes. This case reveals a novel association between a previously unreported heterozygous TNFAIP3 mutation and the development of early-onset complex autoimmunity, validating existing evidence from both genome-wide association studies and conditional murine knockout models that implicates TNFAIP3 in autoimmune pathogenesis. This case also expands the clinical spectrum of germline A20 haploinsufficiency, recently identified in a cohort of patients with Behçet’s-like autoinflammatory disease, and shows that correction of the molecular defect within the haematopoietic cell compartment may be a viable treatment option for severe clinical manifestations.