Phenotypic mosaicism in PNH. Hypothetical histograms of erythrocytes from patients with PNH stained with anti-CD59 are illustrated. The proportion and type of abnormal erythrocytes varies greatly among patients with PNH and these characteristics are important determinants of clinical manifestations. In general, patients with a high percentage of type III erythrocytes have clinically apparent hemolysis (A). If the erythrocytes are partially deficient in GPI-AP, hemolysis may be modest even if the percentage of the affected cells is high (B). A patient may have a diagnosis of PNH, but if the proportion of type III cells is low, only biochemical evidence of hemolysis may be observed (C). Illustration enhanced by A. Y. Chen.