Analysis of CD34(+) cells from PNH patients demonstrated a higher apoptosis rate of CD55(+)CD59(+) cells when compared to GPI-AP-deficient ones and to normal CD34(+) cells, suggesting frailty of progenitor cells in PNH patients more than an advantage of PNH cells [16,17]. This evidence concerns the gene CD59 and paroxysmal nocturnal hemoglobinuria.