Definition of Autoimmune lymphoproliferative syndrome (ALPS)

Autoimmune lymphoproliferative syndrome (ALPS): A disease caused by failure of lymphocytes to die once they have finished doing their job. As a result, lymphocytes hang around in the spleen and lymph nodes which grow large, and immune cells attack the body's own tissues, a condition known as autoimmunity.

ALPS is characterized by:

• Anemia due to excessive destruction of red blood cells hemolytic anemia),
• Decreased platelets in the blood (thrombocytopenia),
• Enlargement of lymph nodes (lymphadenopathy), and
• Enlargement of the spleen (splenomegaly).

On a genetic level there are two types of ALPS. Type I ALPS ("classic" ALPS) is caused by mutations in a cell surface protein called FAS or in its ligand FASL which play a pivotal role in the programmed cell death (a process known as apoptosis) of lymphocytes. Defects in the expression of FAS or FASL result in the abnormal accumulation of mature lymphocytes and in autoimmune disease. Type II ALPS is caused by mutation in caspase-10, a gene involved in the cascade of protease reactions responsible for programmed cell death (apoptosis).

ALPS was first reported in 1967 by Canale and Smith. It is sometimes called the Canale-Smith syndrome.