MHC class II deficiency-4 (MHC2D4) is an autosomal recessive immunodeficiency characterized by the onset of recurrent, persistent infections from birth, resulting in failure to thrive. Infectious agents include bacteria, viruses, fungi, and protozoa, usually affecting the respiratory and gastrointestinal tract. Laboratory studies show decreased CD4+ T cells, hypogammaglobulinemia, an inverted CD4:CD8 ratio, and absence of MHC type II antigens (HLA-DR, -DQ, and DP) on the surface of antigen-presenting cells. Expression of MHC type I antigens may also be decreased (referred to as 'BLS type III'). Patients may die in infancy or early childhood, unless they undergo bone marrow transplantation, which can be curative, although complications are common. MHC2D4 may not be detected by newborn T-cell receptor excision
circle (TREC) screening (summary by Mousavi Khorshidi et al., 2023).
For a discussion of genetic heterogeneity of MHC class II deficiency, see MHC2D1 (209920). [from
OMIM]