Hematopoietic and Immune Systems
Nearly all affected individuals have some blood cell deficiency. Deficiency of T lymphocytes, a subgroup of white blood cells that plays an important role in immunity, is most common (97%) and is usually present at birth. Reductions in both CD4 T cells, which regulate multiple aspects of the immune system and CD8 T lymphocytes, which are important in the control of viruses are typical. However, in addition to a deficit of T lymphocytes, the hematopoietic disturbance can include any or all other blood cell lineages. These hematopoietic cell deficiencies reflect reduced production of these cells by the bone marrow, and affected individuals are more prone than unaffected ones to developing decreased hematopoietic cell levels in the blood as a side effect of drug therapy. Affected individuals are also less responsive to the effects of G-CSF therapy to increase bone marrow production of neutrophils and erythropoietin therapy to increase the bone marrow production or red blood cell precursors.
Because of their immunodeficiency, affected individuals have an increased risk for opportunistic fungal, viral and bacterial infections. They also have an increased risk of more severe infections. The immunodeficiency is also associated with immune dysregulation disorders, such as autoimmune blood diseases.
-National Organization for Rare Disorders