The present report describes and expands the clinical and genetic spectrum of the autoinflammatory disorder, tumor necrosis factor (TNF) receptor-associated periodic syndrome (TRAPS). A total of 20 mutations have been identified since our initial discovery of 6 missense mutations in TNF receptor super family 1A (TNFRSF1A) in 1999. Eighteen of the mutations result in amino acid substitutions within the first 2 cysteine-rich domains (CRDs) of the extracellular portion of the receptor. A single splicing mutation also affects the first CRD by causing the insertion of 4 amino acids. Haplotype analysis of the most commonly occurring and ethnically heterogeneous mutation, R92Q, demonstrates an ancient founder; however, analysis of the T50M mutation, another commonly occurring mutation in Irish and Scottish families, does not, suggesting that T50M is a recurring mutation. Mutations that result in cysteine substitutions demonstrate a higher penetrance of the clinical phenotype (93% versus 82% for noncysteine residue substitutions), and also increase the probability of developing life-threatening amyloidosis (24% versus 2% for noncysteine residue substitutions). Retrospective and prospective evaluation of more than 50 patients, representing 10 of the 20 known mutations, allows us to expand and better define the clinical spectrum of TRAPS. Recurrent episodes of fever, myalgia, rash, abdominal pain, and conjunctivitis that often last longer than 5 days are the most characteristic clinical features of TRAPS. Defective shedding of TNFRSF1A can only partially explain the pathophysiologic mechanism of TRAPS, since some mutations have normal shedding. Consequently, other mechanisms may be mediating the observed phenotype. We are currently investigating other possible mechanisms using stable and transiently transfected cell systems in vitro, as well as developing a knockin mouse model. Preliminary data suggest that etanercept may be effective in decreasing the severity, duration, and frequency of symptoms in TRAPS patients. Additionally, it provides a viable therapeutic alternative to glucocorticoid therapy, which has numerous serious, long-term adverse effects. Two clinical trials are being conducted to evaluate the efficacy of etanercept in decreasing the frequency and severity of symptoms in TRAPS. Lastly, we have summarized data that R92Q and P46L, and probably as yet undiscovered substitutions, represent very low penetrance mutations that may play a much larger role in more broadly defined inflammatory diseases such as rheumatoid arthritis. Our laboratories are currently undertaking both clinical and basic research studies to define the role of these mutations in more common inflammatory diseases.