Novel Developments in Primary Immunodeficiencies (PID)-a Rheumatological Perspective.

The purpose of this review is to provide an overview of the most relevant new disorders, disease entities, or disease phenotypes of primary immune deficiency disorders (PID) for the interested rheumatologist, using the new phenotypic classification by the IUIS (International Union of Immunological Societies) as practical guide. Newly recognized disorders of immune dysregulation with underlying mutations in genes pertaining to the function of regulatory T cells (e.g., CTLA-4, LRBA, or BACH2) are characterized by multiple autoimmune diseases-mostly autoimmune cytopenia-combined with an increased susceptibility to infections due to hypogammaglobulinemia. On the other hand, new mutations (e.g., in NF-kB1, PI3Kδ, PI3KR1, PKCδ) leading to the clinical picture of CVID (common variable immmune deficiency) have been shown to increasingly associate with autoimmune diseases. The mutual association of autoimmune diseases with PID warrants increased awareness of immunodeficiencies when diagnosing autoimmune diseases with a possible need to initiate appropriate genetic tests.