Previous studies have shown that only 35% of WASp-negative patients, especially those aged below 2 years, were found with clinical scores ranging from 1.0 to 2.5, indicative of milder phenotypes; noticeably, an even lower proportion (7%) of WASp-negative patients had mild phenotypes when evaluated at older ages (>2 year) (37).This provides evidence that a mild XLT phenotype may gradually evolve to a more severe disease, and this evolution may take several years. The gene discussed is WAS; the disease is thrombocytopenia 1.