An autosomal recessive immunologic disorder with wide phenotypic variation and severity. Affected individuals usually present in infancy or early childhood with increased susceptibility to infections, often Epstein-Barr virus (EBV), as well as with lymphadenopathy or autoimmune manifestations, predominantly hemolytic anemia. Laboratory studies may show low or normal lymphocyte numbers, often with skewed T-cell subset ratios. The disorder results primarily from defects in T-cell function, which causes both immunodeficiency and overall immune dysregulation. The disease is Monarch Disease Ontology id MONDO_0030457 (immunodeficiency 87 and autoimmunity). Also known as: IMD87, immunodeficiency due to DEF6 deficiency.