[Principles of the diagnostics of inborn errors of immunity].

Inborn errors of immunity (IEI) are a heterogeneous group of nearly 500 diseases characterized by a congenital dysfunction of the immune system. The vast majority of IEIs are rare diseases but all IEIs share a cumulative prevalence of 1:1200-1:2000. In addition to a pathological susceptibility to infections, IEIs can also present with lymphoproliferative, autoimmune or autoinflammatory manifestations. There is often an overlap with classical rheumatic and inflammatory disease patterns. Therefore, a basic knowledge of the clinical presentation and the diagnostics of IEIs is also relevant for the practicing rheumatologist.