A PATIENT WITH PAROXYSMAL-NOCTURNAL HEMOGLOBINURIA BEARING 4 INDEPENDENT PIG-A MUTANT CLONES

Paroxysmal nocturnal hemoglobinuria (PNH) is characterized by clonal b lood cells that are deficient in the surface expression of glycosylpho sphatidylinositol-anchored proteins due to somatic mutation in the X-l inked gene PIG-A. In some patients, more than one abnormal clone may b e present. Analysis of bulk DNA/RNA from granulocytes has been useful in identifying the predominant PIG-A mutation in each patient. However , it is often not useful in determining the presence of minor clones. Many patients have cells with partial deficiency. Here, we analyzed th e PIG-A gene in two B-cell lines bearing complete or partial deficienc ies, cells of hematopoietic progenitor colonies and peripheral blood g ranulocytes from the same patient, We found that hive B-cell lines had different mutations, the granulocytes contained at least two mutants, and the hematopoietic progenitors contained four mutants. Three of th e four were shared by B cells and/or granulocytes whereas the other on e was found only in the hematopoietic progenitors. The partial deficie ncy was caused by a point mutation near an alternative splice site wit hin exon 2 that resulted in partial decreases of activity and quantity of the full-length transcript. These results further show the oligocl onal nature of PNH and differences in extent of expansion among mutant clones. (C) 1997 by The American Society of Hematology.