Most infections are asymptomatic. CMV infection only occurs in people with immune defects, specifically T-cell defects, e.g. AIDS patients and immunosuppressed transplant patients. Infection produces enlargement of cells and nuclear inclusion bodies in a wide range of tissues - systemic infection. Death by the age of 40 is inevitable. XLP is an inherited defect due to a faulty gene on the X chromosome.
Females have two X chromosomes, so if one copy is faulty, the other can usually compensate.
There is no backup X, hence the predominance of the disease in males. SLAM is found on the surface of both B and T cells, effectively coupling them together. When this happens, it signals changes inside the cells that cause them to become active and to develop and proliferate. EBV first infects the throat but shortly afterwards invades the B cells, and triggers them to multiply, partly by increasing the number of SLAM proteins on the surface. Without functional SAP protein, the body is unable to control the B-cell proliferation triggered by infection.