A rare, heterogeneous group of rheumatologic diseases characterized by arthritis which has an onset before 16 years of age, persists for more than 6 weeks, and is of unknown origin.

Sideroblastic anemia with B-cell immunodeficiency, periodic fevers, and developmental delay (SIFD) is an autosomal recessive syndromic disorder characterized by onset of severe sideroblastic anemia in the neonatal period or infancy. Affected individuals show delayed psychomotor development with variable neurodegeneration. Recurrent periodic fevers without an infectious etiology occur throughout infancy and childhood; immunologic work-up shows B-cell lymphopenia and hypogammaglobulinemia. Other more variable features include sensorineural hearing loss, retinitis pigmentosa, nephrocalcinosis, and cardiomyopathy. Death in the first decade may occur (summary by Wiseman et al., 2013).

DFNA34 is an autosomal dominant form of postlingual, slowly progressive sensorineural hearing loss with variable severity and variable additional features. Some patients have pure hearing loss without significant additional features, whereas some patients have features of an autoinflammatory disorder with systemic manifestations, including periodic fevers, arthralgias, and episodic urticaria. The disorder results from abnormally increased activation of the inflammatory pathway, and treatment with an IL1 receptor antagonist (see 147679) may be effective if started early (summary by Nakanishi et al., 2017).