This study is designed to evaluate patients with suspected or identified novel immune disorders, with a focus on abnormal immune homeostasis potentially due to defects in activation or apoptosis. Blood relatives of enrolled patients will also be evaluated. Affected individuals may have Mendelian gene defects involving mostly single or occasionally multiple genes. These patients may have signs and symptoms suggestive of clinically significant lymphocyte homeostasis disorders. However, some selected patients manifesting autoimmunity, autoinflammatory conditions, end-organ dysfunction, Epstein-Barr virus (EBV) and cytomegalovirus (CMV) viremia, frequent infections, allergies, or laboratory abnormalities consistent with immune defects of research interest to the Laboratory of Clinical Infectious Diseases may also be studied under this protocol at the discretion of the Investigators.