The Frequency of Glycophosphatidyl Inositol-Anchored Protein-Negative Paroxysmal Nocturnal Hemoglobinuria Cells in Pediatric Aplastic Anemia Analyzed by Flow Cytometry

Kim, Seok Joo; Kook, Hoon; Cho, Duck; Kim, So Youn; Noh, Ha Young; Choi, Ik Sun; Lee, Joon Sun; Ryang, Dong Wook; Hwang, Tai Ju

Abstract

PURPOSE
Paroxysmal nocturnal hemoglobinuria (PNH) has been known to be a late clonal complication of aplastic anemia (AA). Flow cytometric analysis using CD55 and CD59 antibodies became the gold standard of diagnosing PNH, replacing a traditional, less sensitive Ham's test, as the pathophysiologic mechanism was identified as the deficiency of glycophosphatidyl-inositol anchored protein. Although the incidence of AA seems to be higher in Korea than that of other Western countries, the study of PNH in Korean pediatric AA has never been accomplished. We studied the frequency of PNH in AA, and tried to compare the characteristics of them with those from other countries. METHODS: Twenty-two pediatric AA patients were enrolled for the study. As a control, 5 patients with inherited bone marrow failure syndromes (Fanconi anemia, 1; Diamond-Blackfan anemia, 3; dyskeratosis congenita, 1) and 11 normal children were pooled. For the flow cytometry, 10muL each of CD55-PE and CD59-FITC was mixed with 50muL of whole blood and incubated for 15 min. Red cells were lysed with Q-prep apparatus (Coulter, Fullerton, USA). Beckman Coulter XL flow cytometer was used for the analyses. RESULTS: The median age for the patients was 14 years (range, 2~21). CD55- and CD59-negative cells from controls were 0.13+/-0.18%. Cut-off value for the diagnosis for PNH was designated as > 0.49%, which was mean +2 S.D. of controls. All the patients showed CD55- and CD59-negative PNH cell proportions within the normal ranges, except for a 19-year-old boy who was still cyclosporine-dependent after initial response to immunosuppressive therapy 4 years before. He had 4.79% of CD55- and CD59-negative PNH population. CONCLUSION: The frequency of PNH clones in Korean children with AA was low (1/22=4.5%). This might reflect the relatively low association of PNH in childhood AA, the limitation caused by small numbers of the study population, or true ethnic differences. A further study incorporating more patients seems to be warranted.