WAS participants will be defined as males who have:
1. thrombocytopenia (\< 100K) AND EITHER molecular diagnosis of WAS OR reduced WASP expression; OR
2. thrombocytopenia (\< 100K) AND positive family history consistent with WAS diagnosis; OR
3. chronic thrombocytopenia (\< 100K for minimum of 3 months) AND low mean platelet volume (MPV below normal range for age) AND EITHER recurrent and/or severe infections requiring treatment and/or eczema OR lack of antibody response to polysaccharide antigens or low IgM.
Longitudinal Analysis (Retrospective and Prospective)
1. Stratum A. Participants with WAS who have or will Receive HCT
* Participants with WAS who have received an HCT since January 1, 1990
2. Stratum B. Participants with WAS who have or will Receive Gene Transfer
* Participants in which the intention is to treat with gene transfer with autologous modified cells
Cross-Sectional Analysis (Strata A and B) 1. Participants with WAS who are surviving and at least 2 years after the most recent HCT or gene therapy.
