Hypomethylating agents are associated with high rates of hematologic toxicity in patients with secondary myeloid neoplasms developing after acquired aplastic anemia

Not available.

Disparities in Cytomegalovirus Infection Rates by Race and Ethnicity among Pediatric Allogeneic Hematopoietic Cell Transplantation Recipients at a Single Center

Previous literature has reported cytomegalovirus (CMV) infection rate disparities among racial/ethnic groups of hematopoietic cell transplantation (HCT) recipients. Because race and ethnicity categorizations are social constructs unlikely to affect biological systems, it is likely there are covariates on the pathway to CMV detection, known as mediators, that can explain the observed disparity. Recent developments in mediation analysis methods enable the analysis of time-to-event outcomes, allowing an investigation of these disparities to also consider the timing of CMV infection detection relative to HCT. This study aimed to explore whether racial and ethnic CMV infection disparities existed within a population of HCT recipients at our center, and whether clinical covariates explained any observed association. The study cohort included all recipients of allogeneic HCT performed at the Children's Hospital of Philadelphia between January 2004 and April 2017 who were CMV PCR-negative pretransplantation, had known donor/recipient CMV serology, and were under blood CMV PCR surveillance. Subjects were followed for 100 days post-HCT. Accelerated failure time models using subject's reported race/ethnicity, dichotomized into non-Hispanic White (NHW) and non-NHW, and exposure and time to CMV detection as outcomes examined whether selected clinical factors-donor/recipient CMV serostatus, recipient age, indication for HCT, hematopoietic cell source, match quality-mediated any identified exposure-outcome association. The analysis included 348 HCTs performed in 335 subjects, with 86 episodes (24.7%) in which CMV was detected via PCR analysis. The accelerated failure time model without mediators estimated that non-NHW subjects had fewer CMV-free survival days (time ratio, .21; 95% confidence interval, .10 to .44). Any hypothesized mediator mediated at most 5% of the total association between race/ethnicity and time to CMV detection. Non-NHW HCT recipients had fewer CMV-free survival days than NHW recipients; none of the clinical factors hypothesized to mediate this association accounted for a significant component of total association. Further research should focus on nonclinical factors influenced by systemic racism to better understand their effect on CMV infection among HCT recipients.

Uncovering the Genetic Etiology of Inherited Bone Marrow Failure Syndromes Using a Custom-Designed Next-Generation Sequencing Panel

Inherited bone marrow failure syndromes (IBMFS) are a group of heterogeneous disorders that account for ∼30% of pediatric cases of bone marrow failure and are often associated with developmental abnormalities and cancer predisposition. This article reports the laboratory validation and clinical utility of a large-scale, custom-designed next-generation sequencing panel, Children's Hospital of Philadelphia (CHOP) IBMFS panel, for the diagnosis of IBMFS in a cohort of pediatric patients. This panel demonstrated excellent analytic accuracy, with 100% sensitivity, ≥99.99% specificity, and 100% reproducibility on validation samples. In 269 patients with suspected IBMFS, this next-generation sequencing panel was used for identifying single-nucleotide variants, small insertions/deletions, and copy number variations in mosaic or nonmosaic status. Sixty-one pathogenic/likely pathogenic variants (54 single-nucleotide variants/insertions/deletions and 7 copy number variations) and 24 hypomorphic variants were identified, resulting in the molecular diagnosis of IBMFS in 21 cases (7.8%) and exclusion of IBMFS with a diagnosis of a blood disorder in 10 cases (3.7%). Secondary findings, including evidence of early hematologic malignancies and other hereditary cancer-predisposition syndromes, were observed in 9 cases (3.3%). The CHOP IBMFS panel was highly sensitive and specific, with a significant increase in the diagnostic yield of IBMFS. These findings suggest that next-generation sequencing-based panel testing should be a part of routine diagnostics in patients with suspected IBMFS.

Reduced toxicity matched sibling bone marrow transplant results in excellent outcomes for severe congenital neutropenia

Severe congenital neutropenia (SCN) is caused by germline mutations, most commonly in ELANE, impacting neutrophil maturation and leading to high risk of life-threatening infections. Most patients with ELANE-mutant SCN can achieve safe neutrophil counts with chronic Granulocyte-Colony Stimulating Factor (G-CSF). However, up to 10% of patients have neutropenia refractory to G-CSF and require allogeneic stem cell transplant. Traditional conditioning for these patients includes busulfan and cyclophosphamide which is associated with significant toxicities. We present five patients with SCN without myeloid malignancy transplanted using a reduced toxicity regimen of busulfan, fludarabine and thymoglobulin. 5 pediatric patients with SCN underwent matched sibling donor bone marrow transplant (MSD-BMT) between 2014-2022 on or per CHP14BT057 (NCT02928991), a prospective, single center trial testing elimination of cyclophosphamide from conditioning in pediatric patients with single lineage inherited BMF syndromes. All patients had MSDs and no evidence of MDS. Conditioning consisted of PK-adjusted busulfan, fludarabine, and thymoglobulin, with calcineurin inhibitor and mycophenolate mofetil GVHD prophylaxis. With median follow-up of 48.4 months, overall and event-free survival were 100%. There was no acute GVHD and one instance of chronic limited GVHD. Patients exhibited >95% donor myeloid chimerism at 5 years post-BMT. Two patients experienced CMV reactivation without end-organ disease, and no other viral reactivation or significant infections occurred. MSD-BMT with reduced toxicity myeloablation for SCN provides excellent outcomes while minimizing toxicity. These data suggest that busulfan, fludarabine, and ATG can be considered an efficacious, low-toxicity standard of care regimen for patients with SCN undergoing MSD-BMT.

Management of Fanconi anemia beyond childhood

Fanconi anemia (FA) has long been considered a severe inherited bone marrow failure (BMF) disorder of early childhood. Thus, management of this multisystem disorder has previously been unfamiliar to many hematologists specializing in the care of adolescents and young adults (AYA). The increased diagnosis of FA in AYA patients, facilitated by widely available germline genomic testing, improved long-term survival of children with FA following matched sibling and alternative donor hematopoietic stem cell transplantation (HSCT) performed for BMF, and expanding need in the near future for long-term monitoring in patients achieving hematologic stabilization following ex vivo gene therapy are all reasons why management of FA in AYA populations deserves specific consideration. In this review, we address the unique challenges and evidence-based practice recommendations for the management of AYA patients with FA. Specific topics addressed include hematologic monitoring in AYA patients yet to undergo HSCT, management of myeloid malignancies occurring in FA, diagnosis and management of nonhematologic malignances and organ dysfunction in AYA patients with FA, and evolving considerations for the long-term monitoring of patients with FA undergoing gene therapy.

How I treat cytopenias after CAR T-cell therapy

Increasing use of chimeric antigen receptor T-cell therapy (CAR-T) has unveiled diverse toxicities warranting specific recognition and management. Cytopenias occurring after CAR-T infusion invariably manifest early (<30 days), commonly are prolonged (30-90 days), and sometimes persist or occur late (>90 days). Variable etiologies of these cytopenias, some of which remain incompletely understood, create clinical conundrums and uncertainties about optimal management strategies. These cytopenias may cause additional sequelae, decreased quality of life, and increased resource use. Early cytopenias are typically attributed to lymphodepletion chemotherapy, however, infections and hyperinflammatory response such as immune effector cell-associated hemophagocytic lymphohistiocytosis-like syndrome may occur. Early and prolonged cytopenias often correlate with severity of cytokine release syndrome or immune effector cell-associated neurotoxicity syndrome. Bone marrow biopsy in patients with prolonged or late cytopenias is important to evaluate for primary disease and secondary marrow neoplasm in both pediatric and adult patients. Commonly, cytopenias resolve over time and evidence for effective interventions is often anecdotal. Treatment strategies, which are limited and require tailoring based upon likely underlying etiology, include growth factors, thrombopoietin-receptor agonist, stem cell boost, transfusion support, and abrogation of infection risk. Here we provide our approach, including workup and management strategies, for cytopenias after CAR-T.

Automation of Hematopoietic Cell Transplantation Outcomes Reporting Leads to Dramatic Reduction in Errors Reported to Real-World Data Registry

Institutions that perform hematopoietic cell transplantation (HCT) are required by law to report standardized, structured data on transplantation outcomes. A key post-transplantation outcome is engraftment, the time between HCT infusion and reemergence of circulating neutrophils and platelets. At our center, we found that manual chart abstraction for engraftment data was highly error-prone. We developed a custom R/Shiny application that automatically calculates engraftment dates and displays them in an intuitive format to augment the manual chart review. Our hypothesis was that use of the application to assist with calculating and reporting engraftment dates would be associated with a decreased error rate. The study was conducted at a single tertiary care institution. The application was developed in a collaborative, multidisciplinary fashion by members of an embedded cellular therapy informatics team. Retrospective validation of the application's accuracy was conducted on all malignant HCTs from February 2016 to December 2020 (n = 198). Real-world use of the application was evaluated prospectively from April 2021 through April 2022 (n = 53). The Welch 2-sample t test was used to compare error rates preimplementation and postimplementation. Data were visualized using p charts, and standard special cause variation rules were applied. The accuracy of reported data postdeployment increased dramatically; the engraftment error rate decreased from 15% to 3.8% for neutrophils (P = .003) and from 28% to 1.9% for platelets (P < .001). This study demonstrates the effective deployment of a custom R/Shiny application that was associated with significantly reduced error rates in HCT engraftment reporting for operational, research, and regulatory purposes. Users reported subjective satisfaction with the application and that it addressed difficulties with the legacy manual process. Identifying and correcting erroneous data in engraftment reporting could lead to a more efficient and accurate nationwide assessment of transplantation success. Furthermore, we show that it is possible and practical for academic medical centers to create and support embedded informatics teams that can quickly build applications for clinical operations in a manner compliant with regulatory requirements.

Inherited bone marrow failure with macrothrombocytopenia due to germline tubulin beta class I (TUBB) variant

Germline mutations in tubulin beta class I (TUBB), which encodes one of the β-tubulin isoforms, were previously associated with neurological and cutaneous abnormalities. Here, we describe the first case of inherited bone marrow (BM) failure, including marked thrombocytopenia, morphological abnormalities, and cortical dysplasia, associated with a de novo p.D249V variant in TUBB. Mutant TUBB had abnormal cellular localisation in transfected cells. Following interferon/ribavirin therapy administered for transfusion-acquired hepatitis C, severe pancytopenia and BM aplasia ensued, which was unresponsive to immunosuppression. Acquired chromosome arm 6p loss of heterozygosity was identified, leading to somatic loss of the mutant TUBB allele.

Pathogenicity and impact of HLA class I alleles in aplastic anemia patients of different ethnicities

Acquired aplastic anemia (AA) is caused by autoreactive T cell-mediated destruction of early hematopoietic cells. Somatic loss of human leukocyte antigen (HLA) class I alleles was identified as a mechanism of immune escape in surviving hematopoietic cells of some patients with AA. However, pathogenicity, structural characteristics, and clinical impact of specific HLA alleles in AA remain poorly understood. Here, we evaluated somatic HLA loss in 505 patients with AA from 2 multi-institutional cohorts. Using a combination of HLA mutation frequencies, peptide-binding structures, and association with AA in an independent cohort of 6,323 patients from the National Marrow Donor Program, we identified 19 AA risk alleles and 12 non-risk alleles and established a potentially novel AA HLA pathogenicity stratification. Our results define pathogenicity for the majority of common HLA-A/B alleles across diverse populations. Our study demonstrates that HLA alleles confer different risks of developing AA, but once AA develops, specific alleles are not associated with response to immunosuppression or transplant outcomes. However, higher pathogenicity alleles, particularly HLA-B*14:02, are associated with higher rates of clonal evolution in adult patients with AA. Our study provides insights into the immune pathogenesis of AA, opening the door to future autoantigen identification and improved understanding of clonal evolution in AA.

Does immune destruction drive all forms of bone marrow failure?

Current paradigms of bone marrow failure (BMF) pathophysiology suggest that immune-mediated destruction of hematopoietic stem and progenitor cells (HSPCs) drives acquired aplastic anemia. In contrast, loss of HSPCs due to senescence and/or apoptosis causes BMF in inherited BMF syndromes. In this issue of the JCI, Casado and colleagues challenge this dichotomous conception by demonstrating that NK cell–dependent, immune-mediated hematopoietic suppression and HSPC clearance drive BMF in Fanconi anemia (FA). They show that genotoxic stress upregulates natural killer group 2 member D ligands (NKG2D-L) on FA HSPCs leading to NK cell cytotoxicity through NKG2D receptor activation. Inhibition of NKG2D–NKG2D-L interactions enhanced FA HSPC clonogenic potential and improved cytopenias in vivo. These results provide alternative targets for the development of immunosuppressive therapies to reduce HSPC loss and mitigate the risk of hematologic malignancies in FA.

Hematologic abnormalities in Aicardi Goutières Syndrome

BACKGROUND

Because of the broad clinical spectrum, heritable autoinflammatory diseases present a management and therapeutic challenge. The most common genetic interferonopathy, Aicardi Goutières Syndrome (AGS), is associated with early onset neurologic disability and systemic inflammation. The chronic inflammation of AGS is the result of dysregulation of interferon (IFN) expression by one of nine genes within converging pathways. While each AGS subtype shares common features, distinct patterns of severity and potential for systemic complications amongst the genotypes are emerging. Multilineage cytopenias are a potentially serious, but poorly understood, complication of AGS. As immunomodulatory treatment options are developed, it is important to characterize the role of the disease versus treatment in hematologic abnormalities. This will allow for better understanding and management of cytopenia.

METHODS

In total, 142 individuals with molecularly-confirmed AGS were included. Information on genotype, demographics, and all available hematologic laboratory values were collected from existing medical records. As part of a clinical trial, a subset of this cohort (n = 52) were treated with a janus kinase inhibitor (baricitinib), and both pre- and post-treatment values were included. Abnormal values were graded based on Common Terminology Criteria for Adverse Events (CTCAE v5.0), supplemented with grading definitions for thrombocytosis, and were compared across genotypes and baricitinib exposure.

RESULTS

In total, 11,184 laboratory values were collected over a median of 2.54 years per subject (range 0-22.68 years). To reduce bias from repeated sampling within a limited timeframe, laboratory results were restricted to the most abnormal value within a month (n = 8485). The most common abnormalities were anemia (noted in 24% of subjects prior to baricitinib exposure), thrombocytopenia (9%), and neutropenia (30%). Neutropenia was most common in the SAMHD1 cohort and increased with baricitinib exposure (38/69 measurements on baricitinib versus 14/121 while not on baricitinib). Having an abnormality prior to treatment was associated with having an abnormality on treatment for neutropenia and thrombocytopenia.

CONCLUSION

By collecting available laboratory data throughout the lifespan, we were able to identify novel patterns of hematologic abnormalities in AGS. We found that AGS results in multilineage cytopenias not limited to the neonatal period. Neutropenia, anemia, and thrombocytopenia were common. Moderate-severe graded events of neutropenia, anemia, and leukopenia were more common on baricitinib, but rarely of clinical consequence. Based on these results, we would recommend careful monitoring of hematologic parameters of children affected by AGS throughout the lifespan, especially while on therapy, and consideration of AGS as a potential differential diagnosis in children with neurologic impairment of unclear etiology with hematologic abnormalities. Trial registration ClinicalTrials.gov Identifier: NCT01724580 ClinicalTrials.gov Identifier: NCT03921554.

Comparison of hematopoietic cell transplant conditioning regimens for hemophagocytic lymphohistiocytosis disorders

BACKGROUND

Allogeneic hematopoietic cell transplantation for hemophagocytic lymphohistiocytosis (HLH) disorders is associated with substantial morbidity and mortality.

OBJECTIVE

The effect of conditioning regimen groups of varying intensity on outcomes after transplantation was examined to identify an optimal regimen or regimens for HLH disorders.

METHODS

We studied 261 patients with HLH disorders transplanted between 2005 and 2018. Risk factors for transplantation outcomes by conditioning regimen groups were studied by Cox regression models.

RESULTS

Four regimen groups were studied: (1) fludarabine (Flu) and melphalan (Mel) in 123 subjects; (2) Flu, Mel, and thiotepa (TT) in 28 subjects; (3) Flu and busulfan (Bu) in 14 subjects; and (4) Bu and cyclophosphamide (Cy) in 96 subjects. The day 100 incidence of veno-occlusive disease was lower with Flu/Mel (4%) and Flu/Mel/TT (0%) compared to Flu/Bu (14%) and Bu/Cy (22%) (P < .001). The 6-month incidence of viral infections was highest after Flu/Mel (72%) and Flu/Mel/TT (64%) compared to Flu/Bu (39%) and Bu/Cy (38%) (P < .001). Five-year event-free survival (alive and engrafted without additional cell product administration) was lower with Flu/Mel (44%) compared to Flu/Mel/TT (70%), Flu/Bu (79%), and Bu/Cy (61%) (P = .002). The corresponding 5-year overall survival values were 68%, 75%, 86%, and 64%, and did not differ by conditioning regimen (P = .19). Low event-free survival with Flu/Mel is attributed to high graft failure (42%) compared to Flu/Mel/TT (15%), Flu/Bu (7%), and Bu/Cy (18%) (P < .001).

CONCLUSIONS

Given the high rate of graft failure with Flu/Mel and the high rate of veno-occlusive disease with Bu/Cy and Flu/Bu, Flu/Mel/TT may be preferred for HLH disorders. Prospective studies are warranted.

Betibeglogene Autotemcel Gene Therapy for Non-β0/β0 Genotype β-Thalassemia

BACKGROUND

Betibeglogene autotemcel (beti-cel) gene therapy for transfusion-dependent β-thalassemia contains autologous CD34+ hematopoietic stem cells and progenitor cells transduced with the BB305 lentiviral vector encoding the β-globin (β^A-T87Q) gene.

METHODS

In this open-label, phase 3 study, we evaluated the efficacy and safety of beti-cel in adult and pediatric patients with transfusion-dependent β-thalassemia and a non-β⁰/β⁰ genotype. Patients underwent myeloablation with busulfan (with doses adjusted on the basis of pharmacokinetic analysis) and received beti-cel intravenously. The primary end point was transfusion independence (i.e., a weighted average hemoglobin level of ≥9 g per deciliter without red-cell transfusions for ≥12 months).

RESULTS

A total of 23 patients were enrolled and received treatment, with a median follow-up of 29.5 months (range, 13.0 to 48.2). Transfusion independence occurred in 20 of 22 patients who could be evaluated (91%), including 6 of 7 patients (86%) who were younger than 12 years of age. The average hemoglobin level during transfusion independence was 11.7 g per deciliter (range, 9.5 to 12.8). Twelve months after beti-cel infusion, the median level of gene therapy-derived adult hemoglobin (HbA) with a T87Q amino acid substitution (HbA^T87Q) was 8.7 g per deciliter (range, 5.2 to 10.6) in patients who had transfusion independence. The safety profile of beti-cel was consistent with that of busulfan-based myeloablation. Four patients had at least one adverse event that was considered by the investigators to be related or possibly related to beti-cel; all events were nonserious except for thrombocytopenia (in 1 patient). No cases of cancer were observed.

CONCLUSIONS

Treatment with beti-cel resulted in a sustained HbA^T87Q level and a total hemoglobin level that was high enough to enable transfusion independence in most patients with a non-β⁰/β⁰ genotype, including those younger than 12 years of age. (Funded by Bluebird Bio; HGB-207 ClinicalTrials.gov number, NCT02906202.).

Non-myeloablative conditioning is sufficient to achieve complete donor myeloid chimerism following matched sibling donor bone marrow transplant for myeloproliferative leukemia virus oncogene (MPL) mutation-driven congenital amegakaryocytic thrombocytopenia: Case report

BACKGROUND

Congenital amegakaryocytic thrombocytopenia (CAMT) is a rare platelet production disorder caused mainly by loss of function biallelic mutations in myeloproliferative leukemia virus oncogene (MPL), the gene encoding the thrombopoietin receptor (TPOR). Patients with MPL-mutant CAMT are not only at risk for life-threatening bleeding events, but many affected individuals will also ultimately develop bone marrow aplasia owing to the absence of thrombopoietin/TPOR signaling required for maintenance of hematopoietic stem cells. Curative allogeneic stem cell transplant for patients with CAMT has historically used myeloablative conditioning; however, given the inherent stem cell defect in MPL-mutant CAMT, a less intensive regimen may prove equally effective with reduced morbidity, particularly in patients with evolving aplasia.

METHODS

We report the case of a 2-year-old boy with MPL-mutant CAMT and bone marrow hypocellularity who underwent matched sibling donor bone marrow transplant (MSD-BMT) using a non-myeloablative regimen consisting of fludarabine, cyclophosphamide, and antithymocyte globulin (ATG).

RESULTS

The patient achieved rapid trilinear engraftment and resolution of thrombocytopenia. While initial myeloid donor chimerism was mixed (88% donor), due to the competitive advantage of donor hematopoietic cells, myeloid chimerism increased to 100% by 4 months post-transplant. Donor chimerism and blood counts remained stable through 1-year post-transplant.

CONCLUSION

This experience suggests that non-myeloablative conditioning is a suitable approach for patients with MPL-mutant CAMT undergoing MSD-BMT and is associated with reduced risks of conditioning-related toxicity compared to traditional myeloablative regimens.

Diagnostic work-up for severe aplastic anemia in children: Consensus of the North American Pediatric Aplastic Anemia Consortium

The North American Pediatric Aplastic Anemia Consortium (NAPAAC) is a group of pediatric hematologist-oncologists, hematopathologists, and bone marrow transplant physicians from 46 institutions in North America with interest and expertise in aplastic anemia, inherited bone marrow failure syndromes, and myelodysplastic syndromes. The NAPAAC Bone Marrow Failure Diagnosis and Care Guidelines Working Group was established with the charge of harmonizing the approach to the diagnostic workup of aplastic anemia in an effort to standardize best practices in the field. This document outlines the rationale for initial evaluations in pediatric patients presenting with signs and symptoms concerning for severe aplastic anemia.

Incidence of CMV Infection and Disease and Adverse Events Associated with Antiviral Therapy in a Retrospective Cohort of Allogeneic Hematopoietic Cell Transplant Recipients at an Academic Children's Hospital

BACKGROUND

Cytomegalovirus (CMV) is a significant source of morbidity and mortality among transplant recipients; the epidemiology is less understood in pediatric hematopoietic cell transplantation (HCT) cohorts. Furthermore, there is a paucity of data related to CMV prophylactic and preemptive strategies.

METHODS

A single-center retrospective observational cohort of allogeneic HCT recipients at the Children's Hospital of Philadelphia January 1, 2004-December 31, 2017 was constructed. Subjects were followed for 180 days after transplant to determine whether they had CMV infection or disease. Data on antiviral therapy were collected as were outcomes of CMV disease and adverse events (AEs) related to the antiviral therapy.

RESULTS

Between January 2004 and March 2017, 345 allogeneic HCTs in 333 patients undergoing CMV surveillance testing were identified. CMV DNAemia was detected during the 180-day follow-up in 89 (25.8%) HCTs. CMV recipient-positive transplants were most likely to have CMV infection (47%). Infection rates were high for those receiving a CMV-specific prophylaxis regimen (50%). CMV DNAemia progressed to CMV disease 11.2% of the time. Of 224 subjects receiving CMV-specific prophylaxis, 19.2% experienced ≥1 AE. Of 53 receiving preemptive therapy during any CMV DNAemia episode, 32.1% experienced ≥1 AE.

CONCLUSIONS

CMV infection is common in pediatric allogeneic HCT recipients. The CMV-specific prophylaxis regimen employed in this cohort did not effectively prevent DNAemia, progression to CMV disease was uncommon, and AEs from prophylaxis and preemptive therapy were frequent. Novel approaches that reduce the impact of CMV on pediatric allogeneic HCT recipients are needed.

Standardizing Definitions of Hematopoietic Recovery, Graft Rejection, Graft Failure, Poor Graft Function, and Donor Chimerism in Allogeneic Hematopoietic Cell Transplantation: A Report on Behalf of the American Society for Transplantation and Cellular Therapy

Allogeneic hematopoietic cell transplantation (allo-HCT) is potentially curative for certain hematologic malignancies and nonmalignant diseases. The field of allo-HCT has witnessed significant advances, including broadening indications for transplantation, availability of alternative donor sources, less toxic preparative regimens, new cell manipulation techniques, and novel GVHD prevention methods, all of which have expanded the applicability of the procedure. These advances have led to clinical practice conundrums when applying traditional definitions of hematopoietic recovery, graft rejection, graft failure, poor graft function, and donor chimerism, because these may vary based on donor type, cell source, cell dose, primary disease, graft-versus-host disease (GVHD) prophylaxis, and conditioning intensity, among other variables. To address these contemporary challenges, we surveyed a panel of allo-HCT experts in an attempt to standardize these definitions. We analyzed survey responses from adult and pediatric transplantation physicians separately. Consensus was achieved for definitions of neutrophil and platelet recovery, graft rejection, graft failure, poor graft function, and donor chimerism, but not for delayed engraftment. Here we highlight the complexities associated with the management of mixed donor chimerism in malignant and nonmalignant hematologic diseases, which remains an area for future research. We recognize that there are multiple other specific, and at times complex, clinical scenarios for which clinical management must be individualized.

SLC25A38 congenital sideroblastic anemia: Phenotypes and genotypes of 31 individuals from 24 families, including 11 novel mutations, and a review of the literature

The congenital sideroblastic anemias (CSAs) are a heterogeneous group of inherited disorders of erythropoiesis characterized by pathologic deposits of iron in the mitochondria of developing erythroblasts. Mutations in the mitochondrial glycine carrier SLC25A38 cause the most common recessive form of CSA. Nonetheless, the disease is still rare, there being fewer than 70 reported families. Here we describe the clinical phenotype and genotypes of 31 individuals from 24 families, including 11 novel mutations. We also review the spectrum of reported mutations and genotypes associated with the disease, describe the unique localization of missense mutations in transmembrane domains and account for the presence of several alleles in different populations.

Beyond the storm - subacute toxicities and late effects in children receiving CAR T cells

As clinical advances with chimeric antigen receptor (CAR) T cells are increasingly described and the potential for extending their therapeutic benefit grows, optimizing the implementation of this therapeutic modality is imperative. The recognition and management of cytokine release syndrome (CRS) marked a milestone in this field; however, beyond the understanding gained in treating CRS, a host of additional toxicities and/or potential late effects of CAR T cell therapy warrant further investigation. A multicentre initiative involving experts in paediatric cell therapy, supportive care and/or study of late effects from cancer and haematopoietic stem cell transplantation was convened to facilitate the comprehensive study of extended CAR T cell-mediated toxicities and establish a framework for new systematic investigations of CAR T cell-related adverse events. Together, this group identified six key focus areas: extended monitoring of neurotoxicity and neurocognitive function, psychosocial considerations, infection and immune reconstitution, other end organ toxicities, evaluation of subsequent neoplasms, and strategies to optimize remission durability. Herein, we present the current understanding, gaps in knowledge and future directions of research addressing these CAR T cell-related outcomes. This systematic framework to study extended toxicities and optimization strategies will facilitate the translation of acquired experience and knowledge for optimal application of CAR T cell therapies.

Constrained chromatin accessibility in PU.1-mutated agammaglobulinemia patients

The pioneer transcription factor (TF) PU.1 controls hematopoietic cell fate by decompacting stem cell heterochromatin and allowing nonpioneer TFs to enter otherwise inaccessible genomic sites. PU.1 deficiency fatally arrests lymphopoiesis and myelopoiesis in mice, but human congenital PU.1 disorders have not previously been described. We studied six unrelated agammaglobulinemic patients, each harboring a heterozygous mutation (four de novo, two unphased) of SPI1, the gene encoding PU.1. Affected patients lacked circulating B cells and possessed few conventional dendritic cells. Introducing disease-similar SPI1 mutations into human hematopoietic stem and progenitor cells impaired early in vitro B cell and myeloid cell differentiation. Patient SPI1 mutations encoded destabilized PU.1 proteins unable to nuclear localize or bind target DNA. In PU.1-haploinsufficient pro–B cell lines, euchromatin was less accessible to nonpioneer TFs critical for B cell development, and gene expression patterns associated with the pro– to pre–B cell transition were undermined. Our findings molecularly describe a novel form of agammaglobulinemia and underscore PU.1’s critical, dose-dependent role as a hematopoietic euchromatin gatekeeper.

Case Report: Immune Dysregulation Due to Toxoplasma gondii Reactivation After Allogeneic Hematopoietic Cell Transplant

Disseminated toxoplasmosis is an uncommon but highly lethal cause of hyperferritinemic sepsis after hematopoietic cell transplantation (HCT). We report two cases of disseminated toxoplasmosis from two centers in critically ill adolescents after HCT: a 19-year-old who developed fever and altered mental status on day +19 after HCT and a 20-year-old who developed fever and diarrhea on day +52 after HCT. Both patients developed hyperferritinemia with multiple organ dysfunction syndrome and profound immune dysregulation, which progressed to death despite maximal medical therapies. Because disseminated toxoplasmosis is both treatable and challenging to diagnose, it is imperative that intensivists maintain a high index of suspicion for Toxoplasma gondii infection when managing immunocompromised children, particularly in those with known positive T. gondii serologies.

Diagnosis and treatment of pediatric myelodysplastic syndromes: A survey of the North American Pediatric Aplastic Anemia Consortium

BACKGROUND

Myelodysplastic syndromes (MDS) represent a group of clonal hematopoietic stem cell disorders that commonly progress to acute myeloid leukemia (AML). The diagnostics, prognostics, and treatment of adult MDS are established but do not directly translate to children and adolescents. Pediatric MDS is a rare disease, characterized by unique cytogenetics and histology compared with adult MDS, and often arises secondary to germline predisposition or cytotoxic exposures. Our objective was to highlight aspects of diagnosis/management that would benefit from further systematic review toward the development of clinical practice guidelines for pediatric MDS.

PROCEDURE

The North American Pediatric Aplastic Anemia Consortium (NAPAAC) is composed of collaborative institutions with a strong interest in pediatric bone marrow failure syndromes and hematologic malignancies. The NAPAAC MDS working group developed a national survey distributed to 35 NAPAAC institutions to assess data on (1) clinical presentation of pediatric MDS, (2) diagnostic evaluation, (3) criteria for diagnosis, (4) supportive care and treatment decisions, and (5) role of hematopoietic stem cell transplantation (HSCT).

RESULTS

Twenty-eight of 35 institutions returned the survey. Most centers agreed on a common diagnostic workup, though there was considerable variation regarding the criteria for diagnosis. Although there was consensus on supportive care, treatment strategies, including the role of cytoreduction and HSCT, varied across centers surveyed.

CONCLUSIONS

There is lack of national consensus on diagnosis and treatment of pediatric MDS. This survey identified key aspects of MDS management that will warrant systematic review toward the goal of developing national clinical practice guidelines for pediatric MDS.

Evolution of histomorphologic, cytogenetic, and genetic abnormalities in an untreated patient with MIRAGE syndrome

Gain of function variants in SAMD9 cause MIRAGE syndrome, a rare Mendelian disorder that results in myeloid dysplastic syndrome (MDS), poor immune response, restricted growth, adrenal insufficiency, ambiguous genitalia, feeding difficulties and most often significantly reduced lifespan. In this study, we describe histomorphologic and genetic changes occurring in serial bone marrow measurements in a patient with MIRAGE syndrome and untreated MDS of 9 years. Histomorphological analysis during childhood showed progressive hypocellularity with erythroid and megakaryocytic dysplasia and cytogenetic testing demonstrated monosomy 7. Serial leukemia gene panel testing performed over a seven year period revealed multiple pre-leukemic clones arising at age 7 years followed by sequential mutational events in ETV6 and RUNX1 driving acute myeloid leukemia (AML) at age 9. Comprehensive genotype-phenotype analysis with 28 previously reported patients found the presence of MDS did not impact overall survival, but in silico variant pathogenicity prediction scores for SAMD9 distinguished patients with poor prognosis. Overall, our analysis shows progression of MDS to AML can be monitored by following mutation evolution in leukemia related genes in patients with MIRAGE syndrome, and specific SAMD9 mutations likely influence disease severity and overall survival.

Clinical significance of serial tumor next generation sequencing (NGS) in 155 pediatric cancer patients

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Background: Molecular profiling using NGS technology is critical for tumor diagnosis, risk stratification, and treatment selection. There are limited data in childhood cancers regarding evolution of genomic changes under the selective pressure of chemoradiotherapy. Here we report on serial testing of hematologic and solid pediatric tumor specimens across the spectrum of diagnosis, during treatment and disease relapse. Methods: Since 2016, 2,144 somatic NGS assays from 1,727 unique cancer patients were performed using the Comprehensive Hematological Malignancy Panel (CHMP) or the Comprehensive Solid Tumor Panel (CSTP). Serial tumor analysis was performed on 155 patients. All tumors were profiled for SNVs/indels, copy number alterations (CNAs), and fusions. The clinical impact on diagnosis, prognosis, and therapy was assessed. Results: 85 and 70 patients were tested with CHMP and CSTP, respectively. 86.5% (134/155) of patients underwent 1 subsequent genetic testing, while 13.5% (21/155) were serially tested for 3 - 6 times. Relapsed or therapy-refractory tumor was the most common indication for repeat CHMP and CSTP analysis of tumor genomics (64.5%, 100/155), primarily to survey for new targetable cancer driver mutations. The second most common reason for serial testing with CHMP was to monitor clonal evolution for patients with bone marrow failure syndromes and/or myelodysplastic syndromes, which resulted in a new cancer diagnosis in 14.6% (6/41) patients. For CSTP, the second most common reason for serial testing was to test a different part of the same tumor for tumors with histologic and/or radiographic heterogeneity (27.1%, 19/70). Of all patients with serial testing, 70 had at least one clinically significant new SNV/indel, 44 had distinct CNAs, and 4 had new clinically actionable fusions. Overall, clinically significant new results were detected in 81 (52.3%) patients, including 53 patients with new clonal changes indicating disease evolution, 31 of diagnostic significance, 9 of prognostic significance, and 8 suggesting new treatment options. Conclusions: Taken together, these data highlight the clinical importance of serial testing of pediatric tumors for potential biomarkers that may impact patients’ care at various time points across the spectrum of their diseases.

Partially CD3+-Depleted Unrelated and Haploidentical Donor Peripheral Stem Cell Transplantation Has Favorable Graft-versus-Host Disease and Survival Rates in Pediatric Hematologic Malignancy

Most children who may benefit from stem cell transplantation lack a matched related donor. Alternative donor transplantations with an unrelated donor (URD) or a partially matched related donor (PMRD) carry an increased risk of graft-versus-host-disease (GVHD) and mortality compared with matched related donor transplantations. We hypothesized that a strategy of partial CD3⁺/CD19⁺ depletion for URD or PMRD peripheral stem cell transplantation (PSCT) would attenuate the risks of GVHD and mortality. We enrolled 84 pediatric patients with hematologic malignancies at the Children's Hospital of Philadelphia and the Children's Hospital of Wisconsin between April 2005 and February 2015. Two patients (2.4%) experienced primary graft failure. Relapse occurred in 23 patients (27.4%; cumulative incidence 26.3%), and 17 patients (20.2%) experienced nonrelapse mortality (NRM). Grade III-IV acute GVHD was observed in 18 patients (21.4%), and chronic GVHD was observed and graded as limited in 24 patients (35.3%) and extensive in 8 (11.7%). Three-year overall survival (OS) was 61.8% (95% confidence interval [CI], 50.2% to 71.4%) and event-free survival (EFS) was 52.0% (95% CI, 40.3% to 62.4%). Age ≥15 years was associated with decreased OS (P= .05) and EFS (P= .05). Relapse was more common in children in second complete remission (P = .03). Partially CD3⁺-depleted alternative donor PSCT NRM, OS, and EFS compare favorably with previously published studies of T cell-replete PSCT. Historically, T cell-replete PSCT has been associated with a higher incidence of extensive chronic GVHD compared with limited chronic GVHD, which may explain the comparatively low relapse and NRM rates in our study cohort despite similar overall rates of chronic GVHD. Partial T cell depletion may expand donor options for children with malignant transplantation indications lacking a matched related donor by mitigating, but not eliminating, chronic GVHD.

1745. Retrospective Cohort Analysis to Determine the Incidence of CMV Infection and Disease in Allogeneic Hematopoietic Cell Transplant Recipients at an Academic Children’s Hospital

Background

Data on cytomegalovirus (CMV) infection and disease by donor (D)/recipient (R) status or prophylaxis regimen in pediatric hematopoietic cell transplant (HCT) recipients are limited. There is an absence of data on adverse events (AE) attributable to prophylaxis.

Methods

A single-center cohort (N = 352) of allogeneic HCT episodes between January 2004 and June 2017 was assembled. Exclusion criteria were CMV PCR positivity 30 days before HCT, lack of CMV surveillance (<2 blood PCRs in the 30 days post HCT), or unknown D/R CMV status. CMV prophylaxis was recommended for CMV D+ or R+ patients with ≥1 of the following factors: T-cell depletion, cord blood product, or exposure to distal alemtuzumab. The CMV prophylaxis regimen was standard-dose acyclovir from day −7 to +7, then foscarnet to engraftment, and then valganciclovir to day +100 (acyc → fos → valgan). If a patient did not meet criteria for CMV prophylaxis but was HSV IgG positive then standard-dose acyclovir was given from day −7 to the end of study follow-up (SD-acyc). All remaining patients did not receive antiviral prophylaxis. Outcomes of CMV infection and CMV disease by day +180 were captured. AEs attributable to antiviral prophylaxis were also identified. An AE was attributed to an antiviral prophylaxis medication if the dose was reduced or stopped. AEs were only reported in HCT episodes with complete medical records (n = 221).

Results

The CMV infection rate was 26.7%, with a median time to detection of 23.5 days (range: 4–146). CMV infection was common in D+/R+ (58.9%) and D−/R+ (34.6%) patients. Just under 11% of CMV infections progressed to disease (Figures 1 and 2). Breakthrough CMV infection occurred in 49.1% of patients despite acyc → fos → valgan (Figure 3) at a median of 11 days from HCT (range: 4–132). The attributable AE rate was 13.4% and 36.8% for SD-acyc and acyc → fos → valgan, respectively (Figure 4).

Conclusion

CMV infection was common in D+/R+ and D−/R+ patients, and a substantial proportion progressed to disease. Breakthrough infection persisted despite acyc → fos → valgan prophylaxis and AEs attributable to this regimen were common. CMV infection in R+ patients was frequent even in the absence of additional risk factors. Studies of novel prophylaxis approaches are needed and should include R+ patients regardless of other factors.

Disclosures

All authors: No reported disclosures.

Development of hemolytic paroxysmal nocturnal hemoglobinuria without graft loss following hematopoietic stem cell transplantation for acquired aplastic anemia

PNH is the most common clonal hematopoietic disorder arising in patients with aAA. PNH is caused by mutations in PIGA, a gene that encodes the catalytic subunit of an enzyme involved in the biosynthesis of GPI anchors, transmembrane glycolipids required for cell surface expression of many proteins. PNH clones likely arise as immune escape mechanisms in aAA by preventing CD1D-restricted T-cell recognition of GPI anchors and GPI-linked autoantigens. Though many patients with aAA treated with IST will develop subclinical PNH clones, only a subset will develop PNH disease, characterized by increased thrombosis, intravascular hemolysis, and potential for severe organ dysfunction. In contrast to IST, allogeneic HSCT for patients with aAA is thought to cure bone marrow aplasia and prevent hematopoietic clonal evolution to PNH. Herein, we present a phenomenon of host-derived PNH disease arising in a patient with aAA many years following MSD-BMT, highlighting the importance of monitoring for this clonal disease in aAA patients with stable mixed donor/recipient chimerism after HSCT. We also provide a literature review for similar occurrences of PNH arising after HSCT.

Immunosuppressive therapy for pediatric aplastic anemia: a North American Pediatric Aplastic Anemia Consortium study

Quality of response to immunosuppressive therapy and long-term outcomes for pediatric severe aplastic anemia remain incompletely characterized. Contemporary evidence to inform treatment of relapsed or refractory severe aplastic anemia for pediatric patients is also limited. The clinical features and outcomes for 314 children treated from 2002 to 2014 with immunosuppressive therapy for acquired severe aplastic anemia were analyzed retrospectively from 25 institutions in the North American Pediatric Aplastic Anemia Consortium. The majority of subjects (n=264) received horse anti-thymocyte globulin (hATG) plus cyclosporine (CyA) with a median 61 months follow up. Following hATG/CyA, 71.2% (95%CI: 65.3,76.6) achieved an objective response. In contrast to adult studies, the quality of response achieved in pediatric patients was high, with 59.8% (95%CI: 53.7,65.8) complete response and 68.2% (95%CI: 62.2,73.8) achieving at least a very good partial response with a platelet count ≥50×10⁹L. At five years post-hATG/CyA, overall survival was 93% (95%CI: 89,96), but event-free survival without subsequent treatment was only 64% (95%CI: 57,69) without a plateau. Twelve of 171 evaluable patients (7%) acquired clonal abnormalities after diagnosis after a median 25.2 months (range: 4.3-71 months) post treatment. Myelodysplastic syndrome or leukemia developed in 6 of 314 (1.9%). For relapsed/refractory disease, treatment with a hematopoietic stem cell transplant had a superior event-free survival compared to second immunosuppressive therapy treatment in a multivariate analysis (HR=0.19, 95%CI: 0.08,0.47; P=0.0003). This study highlights the need for improved therapies to achieve sustained high-quality remission for children with severe aplastic anemia.

CD3+/CD19+ Depleted Matched and Mismatched Unrelated Donor Hematopoietic Stem Cell Transplant with Targeted T Cell Addback Is Associated with Excellent Outcomes in Pediatric Patients with Nonmalignant Hematologic Disorders

Unrelated donor hematopoietic stem cell transplantation (HSCT) is increasingly being used to cure nonmalignant hematologic diseases (NMHD) in patients who lack HLA matched related donors. Both graft rejection and graft-versus-host disease (GVHD) remain major barriers to safe and effective transplant for these patients requiring unrelated donors. Partial T cell depletion combined with peripheral stem cell transplantation (pTCD-PSCT) has the potential advantages of providing a high stem cell dose to facilitate rapid engraftment, maintaining cells that may facilitate engraftment, and decreasing GVHD risk compared with T cell-replete HSCT. Here, we report a single-institution, retrospective experience of unrelated donor pTCD-PSCT for pediatric patients with NMHD. From 2014 to 2017, 12 pediatric patients with transfusion-dependent NMHD underwent matched unrelated donor (MUD) or mismatched unrelated donor (MMUD) pTCD HSCT in our center using disease-specific conditioning. Donor PSCs underwent CD3+ T cell and CD19+ B cell depletion using CliniMACS, followed by a targeted addback of 1 × 105 CD3+ T cells/kg to the graft before infusion. All 12 patients demonstrated rapid trilinear engraftment. At a median follow-up of 740days (range, 279 to 1466), all patients were alive with over 92% total peripheral blood donor chimerism and without transfusion dependence or recurrence of their underlying hematologic disease. Immune reconstitution was rapid and comparable with T cell-replete HSCT. No patients developed severe acute GVHD (grades III to IV) or chronic extensive GVHD, and all patients had discontinued systemic immune suppression. Viral reactivations were common, but no patient developed symptoms of life-threatening infectious disease. Our data indicate that MUD and MMUD pTCD-PSCTs are safe and effective approaches that enable rapid engraftment and immune reconstitution, prevent severe GVHD, and expand availability of HSCT to any patients with NMHD who have closely MUDs.

Successful treatment of pulmonary mucormycosis in two pediatric hematopoietic stem cell transplant patients

Pulmonary mucormycosis diagnosed immediately after hematopoietic stem cell transplantation frequently portends a poor prognosis. However, here we describe two cases in children that were treated successfully to highlight the efficacy of a multidisciplinary approach. Despite diagnosis in the immediate post-transplant period and requirement for ongoing immunosuppression to prevent or treat GVHD, both are long-term survivors due to early surgical debridement with transfusion support and prompt initiation of targeted antifungal therapy. In the absence of evidence-based treatment guidelines, survival of pulmonary mucormycosis is achievable even in high-risk patients with a multidisciplinary team to guide management.

Management of Refractory Pediatric Kaposiform Hemangioendothelioma With Sirolimus and Aspirin

Kaposiform hemangioendothelioma (KHE) is a rare vascular tumor characterized by aggressive local invasion and a syndrome of platelet trapping known as Kasabach-Merritt phenomenon that, through deposition of platelet derived growth factors, may perpetuate the growth of the tumor. Although many cases of KHE are successfully treated with local control or low-intensity chemotherapy, some cases are often refractory even to aggressive treatment. Herein, we describe a patient with a refractory, recurrent KHE despite multiple attempts at local control and intensive chemotherapy, that ultimately was successfully treated with rationally designed and low-intensity combination therapy of sirolimus and aspirin.

The Mars Science Laboratory (MSL) Mast cameras and Descent imager: Investigation and instrument descriptions

The Mars Science Laboratory Mast camera and Descent Imager investigations were designed, built, and operated by Malin Space Science Systems of San Diego, CA. They share common electronics and focal plane designs but have different optics. There are two Mastcams of dissimilar focal length. The Mastcam-34 has an f/8, 34 mm focal length lens, and the M-100 an f/10, 100 mm focal length lens. The M-34 field of view is about 20° × 15° with an instantaneous field of view (IFOV) of 218 μrad; the M-100 field of view (FOV) is 6.8° × 5.1° with an IFOV of 74 μrad. The M-34 can focus from 0.5 m to infinity, and the M-100 from ~1.6 m to infinity. All three cameras can acquire color images through a Bayer color filter array, and the Mastcams can also acquire images through seven science filters. Images are ≤1600 pixels wide by 1200 pixels tall. The Mastcams, mounted on the ~2 m tall Remote Sensing Mast, have a 360° azimuth and ~180° elevation field of regard. Mars Descent Imager is fixed-mounted to the bottom left front side of the rover at ~66 cm above the surface. Its fixed focus lens is in focus from ~2 m to infinity, but out of focus at 66 cm. The f/3 lens has a FOV of ~70° by 52° across and along the direction of motion, with an IFOV of 0.76 mrad. All cameras can acquire video at 4 frames/second for full frames or 720p HD at 6 fps. Images can be processed using lossy Joint Photographic Experts Group and predictive lossless compression.

Recent advances in understanding clonal haematopoiesis in aplastic anaemia

Acquired aplastic anaemia (AA) is an immune-mediated bone marrow failure disorder inextricably linked to clonal haematopoiesis. The majority of AA patients have somatic mutations and/or structural chromosomal abnormalities detected as early as at diagnosis. In contrast to other conditions linked to clonal haematopoiesis, the clonal signature of AA reflects its immune pathophysiology. The most common alterations are clonal expansions of cells lacking glycophosphotidylinositol-anchored proteins, loss of human leucocyte antigen alleles, and mutations in BCOR/BCORL1, ASXL1 and DNMT3A. Here, we present the current knowledge of clonal haematopoiesis in AA as it relates to aging, inherited bone marrow failure, and the grey-zone overlap of AA and myelodysplastic syndrome (MDS). We conclude by discussing the significance of clonal haematopoiesis both for improved diagnosis of AA, as well as for a more precise, personalized approach to prognostication of outcomes and therapy choices.

Hematopoietic derived cells do not contribute to osteogenesis as osteoblasts

Despite years of extensive investigation, the cellular origin of heterotopic ossification (HO) has not been fully elucidated. We have previously shown that circulating bone marrow-derived osteoblast progenitor cells, characterized by the immunophenotype CD45-/CD44+/CXCR4+, contributed to the formation of heterotopic bone induced by bone morphogenetic protein (BMP)-2. In contrast, other reports have demonstrated the contribution of CD45+ hematopoietic derived cells to HO. Therefore, in this study, we developed a novel triple transgenic mouse strain that allows us to visualize CD45+ cells with red fluorescence and mature osteoblasts with green fluorescence. These mice were generated by crossing CD45-Cre mice with Z/RED mice that express DsRed, a variant of red fluorescent protein, after Cre-mediated recombination, and then crossing with Col2.3GFP mice that express green fluorescent protein (GFP) in mature osteoblasts. Utilizing this model, we were able to investigate if hematopoietic derived cells have the potential to give rise to mature osteoblasts. Analyses of this triple transgenic mouse model demonstrated that DsRed and GFP did not co-localize in either normal skeletogenesis, bone regeneration after fracture, or HO. This indicates that in these conditions hematopoietic derived cells do not differentiate into mature osteoblasts. Interestingly, we observed the presence of previously unidentified DsRed positive bone lining cells (red BLCs) which are derived from hematopoietic cells but lack CD45 expression. These red BLCs fail to produce GFP even under in vitro osteogenic conditions. These findings indicate that, even though both osteoblasts and hematopoietic cells are developmentally derived from mesoderm, hematopoietic derived cells do not contribute to osteogenesis in fracture healing or HO.

Disrupted lymphocyte homeostasis in hepatitis-associated acquired aplastic anemia is associated with short telomeres

Hepatitis‐associated aplastic anemia (HAA) is a variant of acquired aplastic anemia (AA) in which immune‐mediated bone marrow failure (BMF) develops following an acute episode of seronegative hepatitis. Dyskeratosis congenita (DC) is an inherited BMF syndrome characterized by the presence of short telomeres, mucocutaneous abnormalities, and cancer predisposition. While both conditions may cause BMF and hepatic impairment, therapeutic approaches are distinct, making it imperative to establish the correct diagnosis. In clinical practice, lymphocyte telomere lengths (TL) are used as a first‐line screen to rule out inherited telomeropathies before initiating treatment for AA. To evaluate the reliability of TL in the HAA population, we performed a retrospective analysis of TL in 10 consecutively enrolled HAA patients compared to 19 patients with idiopathic AA (IAA). HAA patients had significantly shorter telomeres than IAA patients (P = 0.009), including four patients with TL at or below the 1st percentile for age‐matched controls. HAA patients had no clinical features of DC and did not carry disease‐causing mutations in known genes associated with inherited telomere disorders. Instead, short TLs were significantly correlated with severe lymphopenia and skewed lymphocyte subsets, features characteristic of HAA. Our results indicate the importance of caution in the interpretation of TL measurements in HAA, because, in this patient population, short telomeres have limited specificity. Am. J. Hematol. 91:243–247, 2016. © 2015 The Authors. American Journal of Hematology Published by Wiley Periodicals, Inc.

Genetic predisposition to myelodysplastic syndrome and acute myeloid leukemia in children and young adults

Myelodysplastic syndrome (MDS) is a clonal blood disorder characterized by ineffective hematopoiesis, cytopenias, dysplasia and an increased risk of acute myeloid leukemia (AML). With the growing availability of clinical genetic testing, there is an increasing appreciation that a number of genetic predisposition syndromes may underlie apparent de novo presentations of MDS/AML, particularly in children and young adults. Recent findings of clonal hematopoiesis in acquired aplastic anemia add another facet to our understanding of the mechanisms of MDS/AML predisposition. As more predisposition syndromes are recognized, it is becoming increasingly important for hematologists and oncologists to have familiarity with the common as well as emerging syndromes, and to have a systematic approach to diagnosis and screening of at risk patient populations. Here, we provide a practical algorithm for approaching a patient with a suspected MDS/AML predisposition, and provide an in-depth review of the established and emerging familial MDS/AML syndromes caused by mutations in the ANKRD26, CEBPA, DDX41, ETV6, GATA2, RUNX1, SRP72 genes. Finally, we discuss recent data on the role of somatic mutations in malignant transformation in acquired aplastic anemia, and review the practical aspects of MDS/AML management in patients and families with predisposition syndromes.