Abstract
To date, the pathogenic mechanisms underlying Schnitzler syndrome remain obscure, in particular, the interplay between the monoclonal protein and increased interleukin-1β (IL-1β) production, although interest in the contribution of genetic factors has been fueled by detection of somatic NLRP3 mosaicism in 2 patients with the variant-type Schnitzler syndrome. At 2 specialist UK centers, we have identified 21 patients who fulfilled diagnostic criteria for Schnitzler syndrome with urticarial rash, fever, arthralgia, and bone pain; 47% reported weight loss, 40% fatigue, and 21% lymphadenopathy. An immunoglobulin M (IgM) κ paraprotein was detected in 86%; the remainder had IgM λ or IgG κ. Patients underwent searches for germ line and somatic mutations using next-generation sequencing technology. Moreover, we designed a panel consisting of 32 autoinflammatory genes to explore genetic susceptibility factor(s) to Schnitzler syndrome. Genetic analysis revealed neither germ line nor somatic NLRP3, TNFRSF1A, NLRC4, or NOD2 mutations, apart from 1 patient with a germ line NLRP3 p.V198M substitution. The proinflammatory cytokines and extracellular apoptosis-associated speck-like protein with caspase recruitment domain (ASC) measured in the serum of Schnitzler syndrome patients during active disease were significantly higher than healthy controls. Ninety-five percent of our cohort achieved a complete response to recombinant IL-1 receptor antagonist (anakinra). Our findings do not support a role for somatic NLRP3 mosaicism in disease pathogenesis; although elevated levels of ASC, IL-6, and IL-18 in patients' serum, and the response to anakinra, suggest that Schnitzler syndrome is associated with upregulated inflammasome activation. Despite its rarity, Schnitzler syndrome is an important diagnosis as treatment with IL-1 antagonists dramatically improves quality of life for patients.