New variant in the IL1RN-gene (DIRA) associated with late-onset, CRMO-like presentation.

OBJECTIVE: To report a chronic recurrent multifocal osteomyelitis (CRMO)-like clinical phenotype with multisystem inflammation associated with a novel gene variant in the spectrum of IL-1-mediated diseases. METHODS: A 3-year-old boy presented with recurrent episodes of fever, serositis, pancreatitis and high inflammatory markers with onset at age 13 months. At age 3 years, he started limping. Imaging revealed multifocal pelvic bone inflammation suggestive of CRMO. Autoinflammation panel testing was non-contributory. Whole exome sequencing (WES) and advanced IL-1 pathway analysis was conducted. RESULTS: WES identified a novel homozygous interleukin receptor 1 (IL1RN) variant (c.62C>G; p. Ser21*) (NM_173842.2). Functional analysis of IL1RN mRNA and IL-1 receptor antagonist (IL-1RA) protein confirmed the diagnosis of a deficiency of the IL-1 receptor antagonist (DIRA). Treatment with the nonselective IL-1 inhibitor anakinra resulting in rapid remission; switch to the selective IL-1beta antagonist canakinumab led to a flare within 6 weeks. Re-start of anakinra recaptured remission, last documented at the recent 19-month follow-up. CONCLUSION: This is the first report of a novel late-onset DIRA confirmed by advanced diagnostic testing. In patients with systemic inflammation and CRMO-like bone lesions, IL1RN testing should be considered; even in the absence of skin manifestations. Non-selective IL-1 inhibition is an effective therapy.