The purpose of the protocol is to allow for patients, and relatives of patients, who may have the newly described autoimmune lymphoproliferative syndrome, to be evaluated at the NIH Clinical Center. This evaluation will include blood and relevant tissue studies along with long-term clinical evaluations to define the biology, inheritance,clinical spectrum, and natural history of this syndrome. The aim of the research is to understand mechanisms involved in the development of expanded numbers of what is typically a rare population of immune cells (CD4-8-/TCRalpha/beta+ T cells, otherwise referred to as double negative T cells), and how these relate to the development of expanded numbers of immune cells and autoimmune (self against self) responses in patients with ALPS.