Inflammatory bowel disease in a young female patient with a novel <i>de novo TRAF3</i> frameshift variant responsive to ustekinumab: a case report

Tumor necrosis factor receptor-associated factor 3 (TRAF3) is an anti-inflammatory molecule that negatively regulates the non-canonical nuclear factor-κB pathway. Although TRAF3 haploinsufficiency (TRAF3 HI) can influence innate and adaptive immune cells, its effect on inflammatory bowel disease (IBD) development remains unclear. Here, we report the first case of severe early-onset IBD with a novel TRAF3 variant leading to HI, successfully treated with ustekinumab. A 6-year-old girl with a recurrent parotitis, otitis media, tonsilitis, and atopic dermatitis developed IBD involving the stomach, small intestine, and colon. At diagnosis, the immunoglobulin (Ig)G and IgA levels were relatively high, and lymphocyte subsets showed increased counts of plasmablasts, class-switch recombination B cells, and circulating T-follicular helper cells. Treatment with azathioprine and infliximab failed to maintain remission marked by several relapses accompanied by erythema nodosum and arthritis; however, ustekinumab, an anti-interleukin (IL)-12/23p40 antibody, led to long-term clinical remission, normalizing the Ig level and reducing abnormal lymphocyte counts. Whole-exome sequencing revealed a novel heterozygous mutation in TRAF3 [p.(Pro487Leufs*8)], resulting in TRAF3 under-expression. Our case may highlight the contribution of TRAF3 HI to the development of IBD and provide insights into IBD pathophysiology, suggesting the involvement of the IL-12/23-T-follicular helper cell pathway affected by genetic mutations.