Autoimmune lymphoproliferative syndrome

Autoimmune lymphoproliferative syndrome (ALPS) is an inherited disorder in which the body cannot properly regulate the number of immune system cells (lymphocytes).

ALPS is characterized by the production of an abnormally large number of lymphocytes (lymphoproliferation). Accumulation of excess lymphocytes results in enlargement of the lymph nodes (lymphadenopathy), the liver (hepatomegaly), and the spleen (splenomegaly).

People with ALPS have an increased risk of developing cancer of the immune system cells (lymphoma) and may also be at increased risk of developing other types of cancers.

Autoimmune disorders are also characteristic of ALPS. Autoimmune disorders occur when the immune system malfunctions and attacks the body's tissues and organs. Most of the autoimmune disorders associated with ALPS damage blood cells. For example, the immune system may attack red blood cells (autoimmune hemolytic anemia), white blood cells (autoimmune neutropenia) or platelets (autoimmune thrombocytopenia). Other autoimmune disorders that may occur in people with ALPS damage the kidneys (glomerulonephritis), liver (autoimmune hepatitis), eyes (uveitis), nerves (Guillain-Barre syndrome), or connective tissues, the material that provides strength and flexibility to structures throughout the body (systemic lupus erythematosus).

Individuals with ALPS may develop skin rashes or hardened skin with painful lumps or patches (panniculitis). Other signs and symptoms such as arthritis, inflammation of blood vessels (vasculitis), mouth sores (oral ulcers), or an early loss of ovarian function (premature ovarian failure) may also occur in this disorder. Affected individuals may also develop neurological damage (organic brain syndrome) with symptoms that may include headaches, seizures, or a loss of intellectual functions (dementia).

ALPS is categorized into several types based mainly on the genetic cause. In the most common form of the disorder, lymphoproliferation generally becomes apparent during childhood. Enlargement of the lymph nodes and spleen frequently occur in affected individuals. Autoimmune disorders typically develop later in life, most frequently as a combination of hemolytic anemia and thrombocytopenia called Evans syndrome. People with this form of ALPS have a greatly increased risk of developing lymphoma compared with the general population.

Other types of ALPS are very rare. In some affected individuals, severe lymphoproliferation begins around the time of birth, and autoimmune diseases and lymphoma develop at an early age. People with this pattern of signs and symptoms generally do not live beyond childhood. One form of ALPS involves lymphoproliferation and the tendency to develop systemic lupus erythematosus. Individuals with this form of the disorder do not have an enlarged spleen.

ALPS is a rare disorder; its prevalence is unknown. More than 100 affected individuals have been identified worldwide.

Mutations in the FAS gene cause ALPS in approximately 75 percent of affected individuals. The FAS gene provides instructions for making a protein involved in cell signaling that results in the self-destruction of cells (apoptosis).

When the immune system is activated to fight an infection, large numbers of lymphocytes are produced. Normally, these lymphocytes are destroyed by apoptosis when they are no longer required, so that they do not attack the body's own tissues. FAS gene mutations result in an abnormal protein that interferes with the initiation of apoptosis. Excess lymphocytes accumulate in the body's tissues and organs, causing the signs and symptoms of ALPS. Interference with apoptosis allows cells to multiply out of control, leading to the lymphomas and other cancers that occur in people with this disorder.

ALPS may also be caused by mutations in additional genes, some of which have not been identified.

Read more about the FAS gene.

See a list of genes associated with ALPS.

This condition is generally inherited in an autosomal dominant pattern, which means one copy of the altered gene in each cell is sufficient to cause the disorder. People with the most severe form of the disorder inherit two altered copies of the gene, one from each parent.