Immunodeficiency

Abstract Immunodeficiency is a condition caused by a defect in the immune system, leading to a failure to protect the body adequately from infection. It should be considered in anybody with a history of recurrent infections, two or more episodes of life‐threatening infections, infections with unusual or opportunistic organisms or with unexpected or severe complications. Immunodeficiency may be either primary or secondary in origin. Primary immunodeficiency (PID) may present as early as the first 3–4 weeks of life with severe diarrhoea, resulting in failure to thrive, recurrent infections and severe eczema. However, it may also manifest in early childhood or later, depending on the nature of the underlying disease and genetic mutation. It is essential to diagnose PID early, particularly severe combined immune deficiency (SCID), in order to prevent infections and organ damage and offer curative treatment such as haematopoietic stem cell transplantation (HSCT) or gene transfer (GT). Key Concepts Defects in the immune system can put patients at risk of life‐threatening infections. Primary immunodeficiency consists of a wide range of disorders that affect adaptive or innate immunity. Early diagnosis of primary immunodeficiency is essential for successful outcome. The most common manifestation of immunodeficiency is recurrent respiratory infections. The most predictive of 10 warning signs for a diagnosis of PID are family history, need for intravenous antibiotics for sepsis and failure to thrive. Next‐generation sequencing has led to the discovery of novel genetic causes of known and new PIDs. Outcome of haematopoietic stem cell transplantation has greatly improved. Gene therapy is successful and increasingly available for a number of disorders. Secondary immunodeficiency can be caused by infection such as HIV.