Bare lymphocyte syndrome

Bare lymphocyte syndrome is a condition caused by mutations in genes of the major histocompatibility complex or in genes involved in processing and presenting MHC molecules, producing a form of severe combined immunodeficiency. In type II, mutations affect transcription factors that regulate MHC class II expression rather than the MHC genes themselves, which severely impairs immune responses because antigen-presenting cells cannot activate CD4-positive T-cells. In type I, MHC class I molecules are absent, leading to recurrent bacterial infections and chronic skin lesions that can progress to serious complications such as bronchiectasis and respiratory failure. The condition is inherited in an autosomal recessive pattern, requiring both parents to carry the mutated gene for a child to be affected.