Wiskott-Aldrich syndrome is characterized by abnormal immune system function (immune deficiency), eczema (an inflammatory skin disorder characterized by abnormal patches of red, irritated skin), and a reduced ability to form blood clots. This condition primarily affects males.

Individuals with Wiskott-Aldrich syndrome have microthrombocytopenia, which is a decrease in the number and size of blood cells involved in clotting (platelets). This platelet abnormality, which is typically present from birth, can lead to easy bruising, bloody diarrhea, or episodes of prolonged bleeding following nose bleeds or minor trauma. Microthrombocytopenia can also lead to small areas of bleeding just under the surface of the skin, resulting in purplish spots called purpura, or variably sized rashes made up of tiny red spots called petechiae. In some cases, particularly if a bleeding episode occurs within the brain, prolonged bleeding can be life-threatening.

Wiskott-Aldrich syndrome is also characterized by abnormal or nonfunctional immune system cells known as white blood cells. Changes in white blood cells lead to an increased risk of several immune and inflammatory disorders in people with Wiskott-Aldrich syndrome. These immune problems vary in severity and include an increased susceptibility to infection from bacteria, viruses, and fungi. People with Wiskott-Aldrich syndrome are at greater risk of developing autoimmune disorders, such as rheumatoid arthritis, vasculitis, or hemolytic anemia. These disorder occur when the immune system malfunctions and attacks the body's own tissues and organs. The chance of developing certain types of cancer, such as cancer of the immune system cells (lymphoma), is also increased in people with Wiskott-Aldrich syndrome.

Wiskott-Aldrich syndrome is often considered to be part of a disease spectrum with two other disorders: X-linked thrombocytopenia and severe congenital neutropenia. These conditions have overlapping signs and symptoms and the same genetic cause.

Mutations in the WAS gene cause Wiskott-Aldrich syndrome. The WAS gene provides instructions for making a protein called WASP. This protein is found in all blood cells. WASP is involved in relaying signals from the surface of blood cells to the actin cytoskeleton, which is a network of fibers that make up the cell's structural framework. WASP signaling triggers the cell to move and attach to other cells and tissues (adhesion). In white blood cells, this signaling allows the actin cytoskeleton to establish interactions between cells and the foreign invaders that they target (immune synapses).

WAS gene mutations that cause Wiskott-Aldrich syndrome lead to a lack of any functional WASP. Loss of WASP signaling disrupts the function of the actin cytoskeleton in developing blood cells. White blood cells that lack WASP have a decreased ability to respond to their environment and form immune synapses. As a result, white blood cells are less able to respond to foreign invaders, causing many of the immune problems related to Wiskott-Aldrich syndrome. Similarly, a lack of functional WASP in platelets impairs their development, leading to reduced size and early cell death. Additionally, the normal process of removing platelets from circulation and taking them to the spleen for destruction also likely contributes to microthrombocytopenia in individuals with Wiskott-Aldrich syndrome.

Because they all have the same genetic cause, Wiskott-Aldrich syndrome, X-linked thrombocytopenia, and severe congenital neutropenia are sometimes collectively referred to as WAS-related disorders.

Normal Function

The WAS gene provides instructions for making a protein called WASP. This protein is found in all blood cells. WASP is involved in relaying signals from the surface of blood cells to the actin cytoskeleton, which is a network of fibers that make up the cell's structural framework. WASP signaling triggers the cell to move and attach to other cells and tissues (adhesion). In white blood cells, which protect the body from infection, this signaling allows the actin cytoskeleton to establish the interaction between cells and the foreign invaders that they target (immune synapse).

Health Conditions Related to Genetic Changes

Wiskott-Aldrich syndrome

More than 350 mutations in the WAS gene have been found to cause Wiskott-Aldrich syndrome, a condition characterized by abnormal immune system function (immune deficiency) and a reduced ability to form blood clots leading to prolonged bleeding episodes.

Most of the mutations lead to the production of an abnormally short, nonfunctional version of WASP or prevent the production of any WASP. As a result, WASP cannot relay signals, which disrupts the function of the actin cytoskeleton in developing blood cells.

White blood cells that lack WASP have a decreased ability to respond to their environment and form immune synapses. As a result, white blood cells are less able to respond to foreign invaders, causing many of the immune problems related to Wiskott-Aldrich syndrome. Similarly, when cells that aid blood clot formation (platelets) lack functional WASP, their development is impaired. A reduction in platelet size and early cell death leads to the bleeding problems in affected individuals. The impairments of white blood cells and platelets are largely responsible for the immune deficiency and bleeding problems characteristic of Wiskott-Aldrich syndrome.

X-linked thrombocytopenia

More than 60 mutations in the WAS gene have been found to cause X-linked thrombocytopenia, a blood disorder characterized by a decrease in the amount and size of platelets, leading to prolonged bleeding episodes. Immune problems such as an increased susceptibility to infections may also occur.

Most of these WAS gene mutations change single protein building blocks (amino acids) in WASP. Mutations typically lead to the production of an altered protein that cannot efficiently relay signals from the cell membrane to the actin cytoskeleton. In people with X-linked thrombocytopenia, these signaling problems primarily affect the development of platelets. In some cases, white blood cells are affected. When WASP function is impaired in white blood cells, these cells are less able to respond to foreign invaders and immune disorders are more likely to occur.

Some WAS gene mutations cause X-linked thrombocytopenia in some individuals and a related condition called Wiskott-Aldrich syndrome (described above) in others. These mutations usually prevent the production of any WASP. It is unknown why some people with these mutations have the relatively mild features of X-linked thrombocytopenia and others have the severe symptoms of Wiskott-Aldrich syndrome. Because they have overlapping features and the same genetic cause, Wiskott-Aldrich syndrome, X-linked thrombocytopenia, and severe congenital neutropenia are sometimes collectively referred to as WAS-related disorders.

Severe congenital neutropenia

MedlinePlus Genetics provides information about Severe congenital neutropenia

Other Names for This Gene

• IMD2
• WASP
• WASP_HUMAN
• WASPA

Genomic Location

• Decreased numbers of platelets (thrombocytopenia), and very small platelets usually present at birth which can result in:
  • Bleeding inside the brain, which can be very fatal
  • Mucosal (such as insed the mouth) bleeding
  • Bloody diarrhea
  • Bruising or purplish areas on the skin or mucous membranes (purpura), caused by bleeding under the skin
  • Pinpoint red spots on the skin (petechiae).
  • Life-threatening bleeding (occurs in 30% of males prior to diagnosis)
• Red patches of red and irritated skin (eczema), ccurs in about 80% of the cases and can be mild to severe
• Other skin diseases such as impetigo, cellulitis, and abscesses
• Increased risk of infections, especially to recurrent bacterial and viral infections, mostly recurrent ear infections and some viruses such as cytomegalovirus (CMV), herpes simplex virus (HSV), Epstein-Barr virus (EBV).
• Increased risk of developing autoimmune disorders (when the immune system mistakenly attacks the body's own tissues and organs) specially when people get older, and that may include hemolytic anemia (destruction of red blood cells), immune thrombocytopenic purpura, rheumatoid arthritis, vasculitis of small and large vessels, and immune-mediated damage to the kidneys and liver
• Increased risk of developing some types of cancer, such as lymphoma, especially in people with WAS who had an EBV infection or are older and have an autoimmune disease.

The estimated incidence of Wiskott-Aldrich syndrome is between 1 and 10 cases per million males worldwide; this condition is rarer in females.