Ter Haar NM, Eijkelboom C, Cantarini L, et al. - Researchers defined the clinical features, treatment response and genetic findings in a large cohort of 187 patients with undefined systemic autoinflammatory diseases (SAIDs). Arthralgia (n = 113), myalgia (n = 86), abdominal pain (n = 89), fatigue (n = 111), malaise (n = 104) and mucocutaneous manifestations (n = 128) were most commonly reported symptoms. In 24 patients, relatives were influenced as well. In 15 patients, genetic variants were discovered in autoinflammatory genes. In comparison with patients without genetic variants, patients with genetic variants more frequently had affected relatives. Most patients reacted well to NSAIDs, corticosteroids, colchicine, and anakinra. Complete remission was seldom accomplished with NSAIDs alone. In patients with distinctive symptoms, significant patterns were observed. Patients with pericarditis (n = 11) were elderly at disease onset (33.8 years) and had fewer episodes per year (3.0/year) in comparison with other patients. Patients with intellectual impairment (n = 8) were younger at disease onset (2.2 years) and usually had relatives affected. In conclusion, this study outlines the clinical features of a large cohort of patients with undefined SAIDs. Moreover, Among these, patients with pericarditis and intellectual impairment seem to include different subsets.