Genetic Basis of Immunodeficiency

This study will examine the role of hereditary factors in different forms of severe combined immunodeficiency (SCID). Patients with immunodeficiencies may be eligible for this study. Candidates include: * Patients with diminished numbers of T cells or NK cells or both, or * Patients with normal T cell and NK cell numbers but diminished T cell, B cell, or NK cell function. Relatives of patients will also be studied. Participants will have blood samples collected for genetic analysis in studies related to SCID at the National Institutes of Health and other institutions.

* INCLUSION CRITERIA: Index cases to be included are those with diminished numbers of T cells and/or NK cells and/or B cells or other immune cells or those who have normal numbers of T cell, B cells, NK cells and other immune cells but diminished function of one or more immune cells. Relatives of affected individuals may also be studied * Patients (index cases): 6 months of age and older * Siblings: 6 months of age and older * Non-sibling relatives (biological parent, aunt, uncle or grandparent): 18 years or older EXCLUSION CRITERIA: * Patients with a known diagnosis * Patients with a particular immunological phenotype that is not of interest to the research conducted under this study. * Pregnancy or lactation * Adults with current decisional impairment