Rare hereditary autoinflammatory disorders: towards an understanding of critical in vivo inflammatory pathways

Hereditary autoinflammatory syndromes are monogenic disorders with an inborn error of innate immunity, and include periodic fever syndromes such as familial Mediterranean fever (FMF), tumor necrosis factor receptor-associated periodic syndrome and cryopyrin-associated periodic syndromes (CAPS), pyogenic diseases such as pyogenic arthritis, pyoderma gangrenosum and acne syndrome (PAPAS), and granulomatous diseases such as Blau syndrome. By identifying the genetic abnormalities and subsequent analyses of the molecular mechanisms underlying these disorders, several critical in vivo pathways for inflammatory processes have been discovered. In this review, three categories of autoinflammatory disorders are discussed: inflammasomopathies, receptor antagonist deficiencies and proteasome disability syndromes. Inflammasomopathies are diseases with dysregulated NLRP3 inflammasome activation, and include CAPS with NLRP3, FMF with MEFV, and PAPAS with PSTPIP1 mutations. Analyses of these diseases have clarified some critical pathways regulating NLRP3 inflammasome signaling. Receptor antagonist deficiencies include the newly defined deficiency for interleukin-1 receptor antagonist resulting in sterile multifocal osteomyelitis with periostosis and pustulosis, and deficiency for interleukin-36 receptor antagonist resulting in generalized pustular psoriasis. The identification of these genetic abnormalities has revealed a critical role for receptor antagonists of IL-1 family cytokines in regulating neutrophil activation/recruitment. Finally, proteasome disability syndromes with PSMB8 mutations include Nakajo-Nishimura syndrome and related disorders distributed globally. Analyses of these diseases have unexpectedly shown a critical role of the ubiquitin-proteasome system in the regulation or homeostasis of inflammation/metabolism. Since there still remain a number of predicted but undefined hereditary autoinflammatory syndromes, further clinical and genetic approaches are required to discover novel in vivo critical inflammatory pathways.