Overexpression of high mobility group AT-hook 2 (HMGA2) is found in a number of benign and malignant tumors, including the clonal PIGA(-) cells in 2 cases of paroxysmal nocturnal hemoglobinuria (PNH) and some myeloproliferative neoplasms (MPNs), and recently in hematopoietic cell clones resulting from gene therapy procedures.