Severe combined immunodeficiency due to CARD11 deficiency is a rare combined T and B cell immunodeficiency characterized by normal numbers of T and B lymphocytes, increased numbers of transitional B cells and hypo- to agammaglobulinemia, decreased numbers of regulatory T cells and defects in T-cell functions. It presents with severe susceptibility to infections, including opportunistic infections. The disease is Monarch Disease Ontology identifier MONDO_0014081 (severe combined immunodeficiency due to CARD11 deficiency). Also known as: SCID due to CARD11 deficiency, immunodeficiency 11A, immunodeficiency type 11.