Bare lymphocyte syndrome type II

Bare lymphocyte syndrome type II (BLS II) is an inherited disorder of the immune system, classed as a form of combined immunodeficiency. People with it lack almost all protection against bacteria, viruses and fungi, so they suffer repeated, persistent and sometimes life-threatening infections, often from opportunistic organisms that rarely trouble people with healthy immune systems. It is usually diagnosed in the first year of life, when infants have persistent infections of the respiratory, gastrointestinal and urinary tracts, absorb nutrients poorly and grow more slowly than their peers. Untreated, the infections lead to organ failure and affected people usually do not survive past early childhood. The name comes from the absence of major histocompatibility complex (MHC) class II proteins on the surface of lymphocytes, which is caused by mutations in the CIITA, RFX5, RFXANK or RFXAP gene, whose proteins control the activity of the MHC class II genes. At least 100 cases have been reported in the medical literature, and the condition appears especially prevalent in the Mediterranean region and North Africa. Because it is the most common and best studied of a group of related conditions, it is often referred to simply as bare lymphocyte syndrome.