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.

Background/Aims: Very early-onset inflammatory bowel disease (VEO-IBD), defined as IBD diagnosed in patients younger than 6 years, is a challenge for pediatric gastroenterologists. Although there have been reports regarding VEO-IBD in Western countries, those in Asia are still lacking. This study aimed to investigate the clinical features of Japanese VEO-IBD patients. Methods: Patients with VEO-IBD diagnosed between 2006 and 2019 were evaluated retrospectively. The disease phenotypes were classified into ulcerative colitis type (UC-type) and Crohn’s disease type (CD-type), and the clinical features and courses were compared between the phenotypes. Results: Overall, 54 VEO-IBD patients (19 patients with UC-type and 35 patients with CD-type) were evaluated. The median age at onset was 18 months. One patient had severe combined immunodeficiency (SCID), and 9 patients had monogenic IBD. Monogenic IBD was more prevalent in the CD-type patients with perianal disease (CD-type (PD)). The age at onset was significantly lower in the CD-type group (P<0.05). The most common initial symptom was bloody stools (70%), followed by diarrhea (63%), weight loss (24%), fever (20%), and perianal disease (20%). Excluding patients with SCID and monogenic IBD, 23 out of 44 patients (52%) required biologics. The biologics were switched in 11 out of 44 patients (25%), and the majority of these patients (82%) were in the CD-type group. Overall, 9 patients (20%) required intestinal resection or ostomy placement. Conclusions CD-type tends to occur at an earlier age, and monogenic IBD occurs significantly more frequently in CD-type (PD). Disease severity and treatment should be individualized, owing to the disease heterogeneity.