Understanding Haploinsufficiency of A20: From Clinical Presentation to Functional Tests

Introduction A20 is a protein encoded by TNFAIP3 gene and acts as a critical negative regulator of inflammation by inhibition of both nuclear factor k light-chain enhancer of activated B cells (NF-kB) and interferon (IFN) signaling pathways. Loss-of-function mutation in TNFAIP3 gene leads to haploinsufficiency of A20 (HA20). We report a patient with HA20: clinical manifestations, laboratory, genetic, and functional tests. Clinical Presentation Female patient presented in her first year of life with recurrent episodes of orogenital aphthosis and perianal ulcers, abdominal pain, and fever. Initially, frequency was biannual, but episodes increased, reaching 3-4 per month by the age of 3 years. Her mother and maternal grandmother had orogenital aphthosis since childhood. Physical Examination Cutaneous-mucous pallor, oral mucosa with 2 ulcers. Weight: 14.4 kg (p10-25). Height: 94 cm (p10). Cardiopulmonary, abdominal, joint, and neurological examination and complementary tests showed no abnormalities. Laboratories Hypochromic microcytic anemia, elevated acute phase reactants and MRP8/14, polyclonal hypergammaglobulinemia. Negative ANA (antinuclear factor), ANCA (antineutrophil cytoplasmic antibody), RF (rheumatoid factor), and anti-thyroid antibodies. Negative stool calprotectin. Genetic Analysis Whole exome sequencing revealed a heterozygous stop codon variant in TNFAIP3 gene, NM_001270507.1:c.547C>T p.(Arg183*), classified as pathogenic (Infevers, ClinVar). Functional Tests (under basal conditions) Flow Cytometry Inflammasome activity showed a marked increase in our patient (9%) vs. healthy control (0.6%). Digital PCR Interferon signature (MX1, ISG15, IFIT1, RSAD2) was significantly increased compared to normal controls (169 vs. 8.4, p<0.0001). NLRP3 and IL-18 RNA levels were significantly increased compared to normal controls (NLRP3: 302 vs. 54, IL-18: 117 vs. 19, p<<0.0001). Conclusion HA20 is a relatively new autoinflammatory disease with incomplete understanding of its pathogenesis. Heterogeneous characteristics make clinical diagnosis a challenge. Genetic and functional tests on inflammasome activity help us in understanding it. The ability of reporting clinical differences allows us to broaden the range of suspicion of disease.