Faculty Bibliography

The mutation rate (mu) is likely to be a key parameter in leukemogenesis, but historically, it has been difficult to measure in humans. The PIG-A gene has some advantages for the detection of spontaneous mutations because it is X-linked, and therefore only one mutation is required to disrupt its function. Furthermore, the PIG-A-null phenotype is readily detected by flow cytometry. Using PIG-A, we have now provided the first in vitro measurement of mu in myeloid cells, using cultures of CD34+ cells that are transduced with either the AML-ETO or the MLL-AF9 fusion genes and expanded with cytokines. For the AML-ETO cultures, the median mu value was approximately 9.4x10(-7) (range approximately 3.6-23x10(-7)) per cell division. In contrast, few spontaneous mutations were observed in the MLL-AF9 cultures. Knockdown of p53 or introduction of mutant NRAS or FLT3 alleles did not have much of an effect on mu. Based on these data, we provide a model to predict whether hypermutability must occur in the process of leukemogenesis.

It has been proposed that genomic instability is essential to account for the multiplicity of mutations often seen in malignancies. Using the X-linked PIG-A gene as a sentinel gene for spontaneous inactivating somatic mutations, we previously showed that healthy individuals harbor granulocytes with the PIG-A mutant (paroxysmal nocturnal hemoglobinuria) phenotype at a median frequency (f) of approximately 12 x 10(-6). Herein, we used a similar approach to determine f in blast cells derived from 19 individuals with acute lymphoblastic leukemia (ALL) and in immortalized Epstein-Barr virus-transformed B-cell cultures (human B-lymphoblastoid cell lines) from 19 healthy donors. The B-lymphoblastoid cell lines exhibited a unimodal distribution, with a median f value of 11 x 10(-6). In contrast, analysis of the f values for the ALL samples revealed at least two distinct populations: one population, representing approximately half of the samples (n = 10), had a median f value of 13 x 10(-6), and the remaining samples (n = 9) had a median f value of 566 x 10(-6). We conclude that in ALL, there are two distinct phenotypes with respect to hypermutability, which we hypothesize will correlate with the number of pathogenic mutations required to produce the leukemia.

BACKGROUND: Paroxysmal nocturnal hemoglobinuria (PNH) is a rare disease in children. The most significant clinical features of PNH include: bone marrow failure, intravascular hemolysis, and thrombosis. To further characterize the clinical presentation and outcome to treatment we performed a retrospective analysis of pediatric patients with PNH. PROCEDURE: We reviewed the medical records of 12 consecutive pediatric patients with PNH diagnosed at our institution from 1992 to 2010. RESULTS: Presenting clinical symptoms included: bone marrow failure (N = 10); gross hemoglobinuria with isolated red cell anemia (N = 1); and jaundice, hepatitis, and isolated thrombocytopenia (N = 1). Immunosuppressive therapy was the initial treatment for 8 patients. Five patients had myelodysplastic features without developing excessive blasts or leukemic transformation. Thrombosis occurred in 6 patients. Five patients underwent hematopoietic stem cell transplant (HSCT) of whom 3 patients are alive and disease-free. Three patients received anti-complement therapy with eculizumab. Two patients died following complications related to thrombosis and 2 patients are transfusion independent with stable disease. CONCLUSION: This report highlights a high rate of bone marrow failure along with a low rate of hemoglobinuria at presentation, a high rate of thrombosis, and for some patients the spontaneous resolution of myelodysplastic features. Delay in diagnosis is common and we recommend appropriate PNH testing in all patients with AA, MDS, unexplained Coombs-negative hemolysis, or thrombosis. While HSCT remains the only curative option the high prevalence of hemolysis and thrombosis should warrant the consideration of early treatment with anti-complement therapy. Pediatr Blood Cancer 2012;59:525-529. (c) 2011 Wiley Periodicals, Inc.

Background Thrombosis is the major risk factor for death in patients with paroxysmal nocturnal hemoglobinuria. Previous case reports indicate that venous thrombosis in patients with paroxysmal nocturnal hemoglobinuria is amenable to thrombolysis. DESIGN AND METHODS: We reviewed the outcome of thrombolytic therapy for patients with paroxysmal nocturnal hemoglobinuria who had thromboses refractory to anticoagulation at our institutions. RESULTS: In this study of 41 patients who had at least one thrombotic event, we confirmed a very high incidence of recurrence despite anticoagulation. Nine patients with thrombosis were regarded as eligible for administration of intravenous tissue plasminogen activator, which was effective in reversing thrombi in all of 15 occasions in which it was given. Serious hemorrhagic complications developed in three cases. At last follow-up visit, of the nine patients treated, three had died, and six were in very good to excellent condition in terms of clinical outcome and radiological findings. The only patient in whom thrombolysis may have contributed to a fatal outcome also had complications of "heparin induced thrombocytopenia with thrombosis", which we diagnosed in three additional patients. In our review of the literature, nine out of 15 patients treated with thrombolysis have had a good outcome. Conclusions Although it is associated with a significant but manageable risk of bleeding, systemic thrombolysis is a highly effective treatment for reversing venous thromboses in patients with paroxysmal nocturnal hemoglobinuria.