Spontaneous nose bleeds and bloody diarrhea are also common and eczema typically develops within the first month of life.

[12] However, this correlation is not perfect, and sometimes the same variant can be seen both in XLT and in WAS (sometimes within two different members of the same family), a concept in genetics referred to as variable expressivity.

[14] CD43, a transmembrane sialoglycoprotein also known as a leukosialin, is part of a greater complex involved in T-cell activation and acts as a sensitive indicator of abnormal, malignant B cell populations.

[citation needed] Defects in this molecule may be detrimental to WAS patients, who are at a much higher risk of autoimmune diseases that may be exacerbated in later-detected B-cell lymphomas.

The diagnosis can be made on the basis of clinical findings, the peripheral blood smear, and low immunoglobulin levels.

The current gold standard for diagnosis is DNA sequence analysis, which can detect WAS and the related disorders XLT and XLN in 95% of patients and carriers.

WAS is primarily a disorder of the blood-forming tissues, so in cases of severe disease (WAS score 3–5) the only widely available curative treatment currently available is a hematopoietic stem cell transplant (HCT).

The greatest mortality risk in WAS before age 30 is from bleeding so aspirin and other nonsteroidal anti-inflammatory drugs that may interfere with already compromised platelet function should generally be avoided.

[26] It has since been proposed the eltrombopag may be used to bridge to HCT in patients with severe thrombocytopenia to normalize platelet numbers without transfusions and decrease bleeding events.

WAS patients with immune system compromise may benefit from antibiotic prophylaxis, for example by taking trimethoprim-sulfamethoxazole to prevent Pneumocystis jirovecii-related pneumonia.

When there are signs or symptoms of an infection, prompt and thorough evaluation is important including blood cultures to guide therapy (often IV antibiotics).

[31] In April 2015 results from a follow-up British and French trial six out of seven individuals showed improvement of immune function and clinical symptoms an average of 27 months after treatment with gene therapy.

[32][33][34] Importantly, neither study showed evidence of leukemic proliferation following treatment, a complication of early attempts at gene therapy using a retroviral vector.

[31][32] A version of this treatment, OTL-103, is being developed by Orchard Therapeutics and (as of 28 June 2021[update]) is undergoing Phase I/II clinical trials.

There is some genotype-phenotype correlation, with most individuals with X-linked thrombocytopenia having missense variants in the WAS gene versus 86.5% of those that make no WAS protein having the classic Wiskott–Aldrich syndrome phenotype.

[38][39] Overall the prognosis for individuals with Wiskott–Aldrich syndrome has improved considerably over the past decades due to earlier diagnoses and more access to treatments.

In 2006, a German research group analyzed family members of Wiskott's three cases, and surmised they probably shared a novel frameshift mutation of the first exon of the WASp gene.