Wiskott-Aldrich syndrome (WAS) is a rare genetic immune disorder that almost exclusively affects boys. It causes three core problems: low platelet counts that lead to excessive bleeding, a weakened immune system that invites repeated infections, and eczema. The condition is present from birth and stems from a mutation on the X chromosome, which is why it overwhelmingly impacts males.
What Causes It
WAS is caused by mutations in a gene called WAS, located on the X chromosome. This gene provides instructions for making a protein (called WASp) that plays a central role in how immune cells and platelets function. WASp helps cells maintain their internal scaffolding, a mesh of protein fibers that gives cells their shape and allows them to move, communicate, and respond to threats. Without functional WASp, immune cells can’t migrate to infection sites properly, can’t form the connections they need to coordinate an immune response, and platelets are produced smaller and in fewer numbers than normal.
Because the gene sits on the X chromosome, boys (who have only one X) are affected if they inherit a single copy of the mutation. Girls (who have two X copies) are typically carriers, since their second X chromosome can compensate. The severity of the disease depends heavily on the specific mutation. Some mutations eliminate WASp entirely and cause classic, severe WAS. Others reduce it partially, leading to a milder form called X-linked thrombocytopenia, where bleeding is the primary problem and immune deficiency is less pronounced.
The Three Hallmark Features
Low Platelet Count and Bleeding
Thrombocytopenia, or a low platelet count, is present at birth and is the most common finding at the time of diagnosis. Platelet counts typically range from 20,000 to 50,000 per cubic millimeter (normal is 150,000 to 400,000) and can drop below 10,000. Crucially, the platelets that are produced are abnormally small. This combination of too few and too small platelets creates a significant bleeding risk.
Newborns may show tiny red or purple dots on the skin (petechiae), prolonged bleeding from the umbilical stump, or excessive bleeding after circumcision. As children grow, nosebleeds, bloody stool, blood in urine, and bleeding gums are common. The most dangerous complication is intracranial bleeding. In some infants under age two, platelet counts become severely low and resistant to treatment, likely because the body starts producing antibodies against its own platelets.
Eczema
About half of children with WAS develop eczema during the first year of life. It resembles typical atopic dermatitis, with dry, itchy, inflamed patches of skin, but in classic severe WAS the eczema tends to be extensive and harder to manage. It can range from mild patches to widespread, weeping skin inflammation that significantly affects quality of life.
Recurrent Infections
Children with WAS are vulnerable to a wide range of infections because both their antibody-producing cells and their infection-fighting white blood cells are impaired. Common bacterial culprits include Streptococcus pneumoniae, Haemophilus influenzae, and Neisseria meningitidis, bacteria that are normally kept in check by a healthy immune system. These lead to frequent ear infections, sinus infections, pneumonia, meningitis, and bloodstream infections.
The immune deficiency also opens the door to opportunistic infections that rarely trouble healthy children: a type of pneumonia caused by Pneumocystis jirovecii, widespread chickenpox or CMV infections, and the viral skin condition molluscum contagiosum. Fungal infections, primarily oral thrush from Candida, can occur as well, though they’re less common. Many children also experience failure to thrive, meaning they don’t gain weight or grow at expected rates.
Autoimmune Problems and Cancer Risk
Beyond the classic triad, WAS carries a high risk of autoimmune disease, where the immune system turns against the body’s own tissues. Somewhere between 22% and 72% of patients develop autoimmune complications, a remarkably wide range that reflects differences in disease severity and how patients are studied. The most common is autoimmune hemolytic anemia, where the body destroys its own red blood cells, occurring in about 36% of patients. Inflammation of blood vessels (vasculitis) and joint inflammation each affect roughly 29%, while immune-related drops in white blood cells affect about 25%. Inflammatory bowel disease and kidney disease from antibody deposits are less frequent but recognized complications.
Patients with WAS also face an elevated cancer risk. Between 13% and 22% develop tumors, and roughly 90% of those cancers originate in the lymphatic system. Non-Hodgkin lymphoma is the most common type. These cancers tend to carry a worse prognosis in WAS patients than in the general population, which is one reason early, definitive treatment of the underlying syndrome is so important.
How It’s Diagnosed
The combination of low platelet count with unusually small platelets in a baby boy is one of the strongest initial clues. Most blood disorders that cause low platelets produce normal-sized or large platelets, so small platelet size helps distinguish WAS from other causes. A typical mean platelet volume in WAS falls below the normal range of 7.4 to 9.5 femtoliters.
From there, blood tests can measure the level of WASp in white blood cells using a technique called flow cytometry. Absent or reduced WASp strongly supports the diagnosis. Genetic testing of the WAS gene confirms it definitively and also helps predict severity: mutations that completely eliminate the protein tend to cause classic severe WAS, while those that allow some protein production are more often associated with the milder X-linked thrombocytopenia.
Managing Day-to-Day Symptoms
Because the immune system can’t produce effective antibodies on its own, most patients receive regular infusions of immunoglobulin, essentially a concentrated dose of protective antibodies collected from donor blood. These infusions, given intravenously every few weeks, help bridge the gap in immune protection. Patients also typically take daily preventive antibiotics to reduce the risk of certain bacterial and fungal infections, particularly Pneumocystis pneumonia.
Eczema is managed with the same approaches used for atopic dermatitis: moisturizers, topical anti-inflammatory creams, and avoiding triggers. Bleeding episodes may require platelet transfusions, especially during surgery or severe bleeding events. Contact sports and activities with high injury risk are generally avoided to reduce the chance of dangerous bleeding.
Stem Cell Transplant: The Definitive Treatment
A stem cell transplant (also called a bone marrow transplant) is currently the only established cure for Wiskott-Aldrich syndrome. It replaces the faulty blood-forming stem cells with healthy donor cells that can produce functional WASp. When a well-matched donor is available, typically a sibling with identical tissue markers, outcomes are strong: overall survival reaches about 90% with long-term follow-up averaging 11 years. When donors are less well matched, survival drops to around 50%, though advances in transplant techniques continue to improve these numbers.
The transplant process involves chemotherapy to make room for the new donor cells, followed by an infusion of the donor stem cells and weeks to months of recovery as the new immune system establishes itself. Younger age at transplant generally predicts better outcomes, which is why early diagnosis matters so much.
Gene Therapy as an Alternative
For patients who lack a suitable donor, gene therapy has emerged as a promising option. The approach uses a modified virus to deliver a working copy of the WAS gene into the patient’s own blood-forming stem cells, which are then returned to the body. In a clinical trial following eight patients for a median of 7.6 years after treatment, gene-corrected cells engrafted stably, severe infections and eczema resolved, and spontaneous bleeding episodes decreased significantly in both frequency and severity. Three patients achieved platelet counts above 140,000 per microliter, within the normal range.
One patient in the trial died seven months after gene therapy from complications of a pre-existing infection, not from the therapy itself. No other serious treatment-related adverse events were reported over the follow-up period. While these results are encouraging, gene therapy for WAS remains available primarily through specialized centers and clinical trials rather than as a routine treatment option.