Hierarchical Clonal Architecture In Paroxysmal Nocturnal Hemoglobinuria: Stepwise Acquisition of Mutations. Homo sapiens

Paroxysmal nocturnal hemoglobinuria (PNH) is a non-malignant clonal disease of hematopoietic stem cells associated with hemolysis, marrow failure, and thrombophilia. PNH has been considered a monogenic disease due to somatic mutations in PIGA, defects which lead to a deficiency of cell membrane expressed GPI-anchored proteins. Lack of certain GPI-anchored proteins is hypothesized to provide the mutant clone with an extrinsic growth advantage, but some features of PNH also argue for the existence of intrinsic drivers of clonal expansion. Whole exome next generation sequencing (NGS) of paired PNH+ and PNH- fractions from 12 patient samples followed by targeted deep NGS of an additional 36 PNH patients led to the discovery of somatic mutations resulting, in some cases, in a complex hierarchical clonal architecture similar to that observed in myeloid neoplasms. Genes affected include those involved in the pathogenesis of myeloid neoplasms such as TET2, SUZ12, U2AF1 and JAK2. Our data demonstrate that such mutations arose either as a subclone within the PIGA mutant population, or as initial genetic events prior to a PIGA mutation. Accessory genetic events beyond PIGA mutations are frequent in PNH, illustrating a stepwise clonal evolution derived from a singular stem cell clone.