The first reported case of compound heterozygous IL1RN mutations causing deficiency of the interleukin-1 receptor antagonist.

Interleukin-1 receptor antagonist (IL-1Ra) deficiency is a rare autoinflammatory disease involving neonatal onset of pustulosis, periostitis, and sterile osteomyelitis. We report the case of a 2-week-old male who presented with a swollen, erythematous left index finger and elevated serum markers of inflammation. He later developed cyclical fevers, diffuse pustular skin lesions, and thrombus formation. After not responding to broad-spectrum antimicrobial therapy and achieving only moderate success with systemic steroid therapy, he was ultimately treated with recombinant IL-1Ra, anakinra, and experienced significant clinical improvement. Sequencing of his IL1RN gene revealed that the patient was compound heterozygous for a known mutation (E77X) associated with IL-1Ra deficiency and a novel mutation in exon 2 of the gene (c.140delC; p.T47TfsX4). His case highlights IL-1Ra deficiency as an autoinflammatory disease that is distinct from neonatal-onset multisystem inflammatory disease but that also responds well to anakinra. Our patient is the first reported compound heterozygote for E77X and the novel mutation in exon 2 of the gene, the latter of which adds to what will surely be a growing database of pathologic mutations in IL1RN.