Immunodeficiency by defective expression of HLA class 1 is a very rare, primary, genetic, immunodeficiency disorder characterized by partial or complete absence of human leukocyte antigen class I expression resulting in a non-specific clinical picture of impaired immune response and susceptibility to infections. The disease is Monarch Disease Ontology identifier MONDO_0011476 (MHC class I deficiency). Also known as: BLS, type I, BLSI, Bare lymphocyte syndrome type 1, HLA CLASS I deficiency, bare lymphocyte syndrome type I, immunodeficiency by defective expression of HLA class 1, immunodeficiency by defective expression of HLA class type 1.