ZAP-70 (zeta-associated protein 70) deficiency is impaired T-cell activation caused by a signaling defect.
ZAP-70 is important in T-cell signaling and in T-cell selection in the thymus. ZAP-70 deficiency causes T-cell activation defects.
Patients who have ZAP-70 deficiency present during infancy or early childhood with recurrent infections similar to those in severe combined immunodeficiency (SCID); however, they live longer, and the deficiency may not be diagnosed until they are several years old. Patients have normal, low, or elevated serum immunoglobulin levels and normal or elevated numbers of circulating CD4 T cells but essentially no CD8 T cells. Their CD4 T cells do not respond to mitogens or allogeneic cells in vitro and do not produce cytotoxic T cells. In contrast, natural killer cell activity is normal.
Diagnosis of ZAP-70 deficiency is similar to that for SCID.
The disorder is fatal unless treated by hematopoietic stem cell transplantation.