Haar NMT, et al. - Clinical and genetic data from 187 subjects with undefined systemic autoinflammatory diseases (SAIDs) were extracted from the Eurofever registry (an international web-based registry that retrospectively gathers clinical information on subjects with autoinflammatory diseases) by the researchers in order to define the clinical features, treatment response and genetic conclusions in a large cohort of subjects with undefined SAIDs. Chronic disease course and recurrent disease course was observed in 7 and 180 subjects, respectively. At disease onset, the median age was 4.3 years. With a median term of 4 days, subjects had a median of 12 episodes per year. Arthralgia (n=113), myalgia (n=86), abdominal pain (n=89), fatigue (n=111), malaise (n=104) and mucocutaneous manifestations (n=128) were most generally reported symptoms. Relatives were affected too in 24 cases. Genetic variants were discovered in autoinflammatory genes in 15 subjects. In comparison with subjects without genetic variants, cases with genetic variants more frequently had affected relatives. Most cases responded fine to non-steroidal anti-inflammatory drugs (NSAIDs), corticosteroids, colchicine, and anakinra. With NSAIDs alone, complete remission was seldom attained. In subjects with distinctive symptoms, striking patterns were obtained. In contrast with other patients, cases with pericarditis (n=11) were older at disease onset and had lesser episodes per year. Subjects with intellectual impairment (n=8) were younger at disease onset and frequently had relatives affected. Hence, the study reported the clinical features of a large cohort of subjects with undefined SAIDs. Moreover, cases of pericarditis and intellectual impairment seemed to comprise distinct subsets among these subjects.