Karyotypic and Genetic Abnormalities Associated with Clonal Evolution in Paroxysmal Nocturnal Hemoglobinuria

• Published in: Blood 2012-11, Vol.120 (21), p.2371-2371
• Main Authors: Makishima, Hideki, Yoshida, Kenichi, Clemente, Michael J., Sanada, Masashi, Nagata, Yasunobu, Afable, Manuel G., Jerez, Andres, Chiba, Kenichi, Shiraishi, Yuichi, Miyano, Satoru, Ogawa, Seishi, Maciejewski, Jaroslaw P.
• Format: Article
• Language: English
• ISSN: 0006-4971; 1528-0020
• DOI: 10.1182/blood.V120.21.2371.2371

Abstract 2371 PNH is a clonal stem cell disease. While nonmalignant, PNH shows certain similarities to MDS and other neoplasms affecting hematopoietic stem and progenitor cells, including persistence of an aberrant clone, clonal expansion, and phenotypic abnormalities. In a small proportion of patients, subtle chromosomal abnormalities can be found and cases of otherwise classical PNH due to microdeletions involving the PIG-A locus have been described, illustrating similarities to other malignant conditions. PIG-A gene mutations lead to defective biosynthesis of GPI anchors and are responsible for the PNH phenotype. Similarly, phenotypic features of stem cells affected by PIG-A mutations are believed to be responsible for the extrinsic growth advantage and clonal expansion in the context of immune mediated suppression of hematopoiesis. While this scenario is plausible, there are also observations suggesting that intrinsic factors may be also involved. For instance, PNH persists after successful immunosuppression, often for many years, suggesting activation of stem cell maintenance genes. Furthermore, PNH clones can also be encountered (albeit at a very low frequency) in healthy individuals, and PNH can present in a pure form without aplastic anemia. Such extrinsic factors may include additional, secondary genetic events such as somatic mutations. Supporting this theory, clonal rearrangement of chromosome 12, which leads to overexpression of the transcription factor HMGA2 gene, were found in cells with the PIG-A mutation from 2 PNH cases. Also, we recently reported 3 PNH cases with JAK2 V617F mutation, who presented with a MPN phenotype and thrombosis. We theorized that study of clonal architecture in PNH will reveal clues as to the pathogenesis of clonal evolution of the PNH stem cell. We applied next generation whole exome sequencing to detect somatic mutations in PNH cases (N=6). The subsequent validation set included 45 PNH cases. PNH and non-PNH cells were sorted using magnetic beads. DNA from both fractions was analyzed by whole exome sequencing and results of the non-PNH cells were subtracted from the results of the PNH clone. We found biallelic PIG-A mutations in 2 female cases and a single mutation in each male case. In an index female case with thrombosis, a novel somatic heterozygous mutation of NTNG1 (P24S) was detected, while the patient was negative for the JAK2 mutation. Allelic frequency with the NTNG1 mutation (53/160 sequence reads (33%))