Presence of the Ile294Thr or Ser272Pro WASp mutation profoundly impaired myelopoiesis and led to increased levels of hematopoietic cell apoptosis. (A) CD34⁺ cell expansion after 14 days in liquid culture. (B) Annexin V–positive cells following anti-CD95 administration to cultured PB lymphocytes. Error bar indicates 1 SD from 33 healthy donors. (C) Spontaneous apoptosis in bone marrow progenitor cells.