recombination activating 2
The RAG2 gene provides instructions for making a member of a group of proteins called the RAG complex. This complex is active in immune system cells (lymphocytes) called B cells and T cells. These cells have special proteins on their surface that recognize foreign invaders and help protect the body from infection. These proteins need to be diverse to be able to recognize a wide variety of substances. The genes from which these proteins are made contain segments known as variable (V), diversity (D), and joining (J) segments. During protein production within lymphocytes, these gene segments are rearranged in different combinations to increase variability of the resulting proteins. The RAG complex is involved in this process, which is known as V(D)J recombination.
During V(D)J recombination, the RAG complex attaches (binds) to a section of DNA called a recombination signal sequence (RSS), which is next to a V, D, or J segment. The RAG complex makes small cuts in the DNA between the segment and the RSS so the segment can be separated and moved to a different area in the gene. This process of DNA rearrangement within B cells and T cells is repeated multiple times in different areas so that the V, D, and J segments are arranged in various combinations. The variety of proteins produced throughout life following V(D)J recombination provides greater recognition of foreign invaders and allows the body to fight infection efficiently.
More than 20 mutations in the RAG2 gene have been found to cause an immune system disorder called Omenn syndrome. This condition is a type of severe combined immunodeficiency (SCID), which is a group of disorders characterized by an almost total lack of immune protection from foreign invaders such as bacteria, viruses, and fungi. Omenn syndrome is characterized by a reduced ability to fight infections and autoimmunity, in which the immune system attacks the body's own tissues and organs. Without treatment, Omenn syndrome is often fatal in infancy.
Most of the RAG2 gene mutations that cause Omenn syndrome change single protein building blocks (amino acids) in the RAG2 protein. These changes can impair RAG complex formation and function, including its ability to bind to DNA. As a result, V(D)J recombination is diminished and the diversity of proteins on the surface of B cells and T cell is severely limited, impairing the cells' ability to recognize foreign invaders and fight infections. The abnormal B and T cells result in the frequent, life-threatening infections of Omenn syndrome. The decrease in lymphocyte function leads to a reduction in the numbers of B cells, but the number of T cells is typically normal. The abnormal T cells attack the body's own cells and tissues, accounting for the autoimmune features of Omenn syndrome.
RAG2 gene mutations can cause other disorders of the immune system (immunodeficiencies). Mutations that completely eliminate the production or function of the RAG2 protein cause a form of SCID that is associated with few or no B cells or T cells. Individuals with this form of SCID have recurrent, persistent infections beginning in infancy, which are usually fatal within the first year of life.
RAG2 gene mutations that result in the production of RAG2 proteins that retain some normal function cause another form of immunodeficiency. This condition is characterized by somewhat reduced numbers of B and T cells, but affected individuals typically do not develop severe infections until late childhood. People with this form of immunodeficiency may also have areas of inflammation (granulomas) in various tissues that can cause tissue damage.
- recombination activating gene 2
- V(D)J recombination-activating protein 2
- Immunobiology: The Immune System in Health and Disease (fifth edition, 2001): Lymphocyte Development Occurs in Specialized Environments and is Regulated by the Somatic Rearrangement of the Antigen-receptor Genes
- Immunobiology: The Immune System in Health and Disease (fifth edition, 2001): The Rearrangement of Antigen-receptor Gene Segments Controls Lymphocyte Development
- Madame Curie Bioscience Database: V(D)J Rearrangement
- Molecular Biology of the Cell (fourth edition, 2002): The Generation of Antibody Diversity