is an autosomal recessive form of severe combined immunodeficiency (SCID) characterized by erythroderma (skin redness), desquamation (peeling skin), alopecia (hair loss), chronic diarrhea, failure to thrive, lymphadenopathy (enlarged lymph nodes), eosinophilia, hepatosplenomegaly, and elevated serum IgE levels. Patients are highly susceptible to infection and develop fungal, bacterial, and viral infections typical of SCID. In this syndrome, the SCID is associated with low IgG, IgA, and IgM and the virtual absence of B cells. There is an elevated number of T cells, but their function is impaired. Omenn syndrome has been found to be caused by mutations in the RAG1 or RAG2 genes. Additional causative genes have been identified. Early recognition of this condition is important for genetic counseling and early treatment. If left untreated, Omenn syndrome is fatal. The prognosis may be improved with early diagnosis and treatment with compatible bone marrow or cord blood stem cell transplantation. Source: Genetic and Rare Diseases Information Center (GARD), supported by ORDR-NCATS and NHGRI.