Lessons from mouse models in the impact of risk factors on the genesis of childhood B-cell leukemia.

B-cell acute lymphoblastic leukemia (B-ALL) stands as the primary contributor to childhood cancer-related mortality on a global scale. The development of the most conventional forms of this disease has been proposed to be conducted by two different steps influenced by different types of risk factors. The first step is led by a genetic insult that is presumably acquired before birth that transforms a healthy cell into a preleukemic one, which is maintained untransformed until the second step takes place. This necessary next step to leukemia development will be triggered by different risk factors to which children are exposed after birth. Murine models that recap the stepwise progression of B-ALL have been instrumental in identifying environmental and genetic factors that contribute to disease risk. Recent evidence from these models has demonstrated that specific environmental risk factors, such as common infections or gut microbiome dysbiosis, induce immune stress, driving the transformation of preleukemic cells, and harboring genetic alterations, into fully transformed leukemic cells. Such models serve as valuable tools for investigating the mechanisms underlying preleukemic events and can aid in the development of preventive approaches for leukemia in child. Here, we discuss the existing knowledge, learned from mouse models, of the impact of genetic and environmental risk factors on childhood B-ALL evolution and how B-ALL prevention could be reached by interfering with preleukemic cells.

Immune stress suppresses innate immune signaling in preleukemic precursor B-cells to provoke leukemia in predisposed mice.

The initial steps of B-cell acute lymphoblastic leukemia (B-ALL) development usually pass unnoticed in children. Several preclinical studies have shown that exposure to immune stressors triggers the transformation of preleukemic B cells to full-blown B-ALL, but how this takes place is still a longstanding and unsolved challenge. Here we show that dysregulation of innate immunity plays a driving role in the clonal evolution of pre-malignant Pax5+/- B-cell precursors toward leukemia. Transcriptional profiling reveals that Myd88 is downregulated in immune-stressed pre-malignant B-cell precursors and in leukemic cells. Genetic reduction of Myd88 expression leads to a significant increase in leukemia incidence in Pax5+/-Myd88+/- mice through an inflammation-dependent mechanism. Early induction of Myd88-independent Toll-like receptor 3 signaling results in a significant delay of leukemia development in Pax5+/- mice. Altogether, these findings identify a role for innate immunity dysregulation in leukemia, with important implications for understanding and therapeutic targeting of the preleukemic state in children.

Childhood B-Cell Preleukemia Mouse Modeling.

Leukemia is the most usual childhood cancer, and B-cell acute lymphoblastic leukemia (B-ALL) is its most common presentation. It has been proposed that pediatric leukemogenesis occurs through a "multi-step" or "multi-hit" mechanism that includes both in utero and postnatal steps. Many childhood leukemia-initiating events, such as chromosomal translocations, originate in utero, and studies so far suggest that these "first-hits" occur at a far higher frequency than the incidence of childhood leukemia itself. The reason why only a small percentage of the children born with such preleukemic "hits" will develop full-blown leukemia is still a mystery. In order to better understand childhood leukemia, mouse modeling is essential, but only if the multistage process of leukemia can be recapitulated in the model. Therefore, mouse models naturally reproducing the "multi-step" process of childhood B-ALL will be essential to identify environmental or other factors that are directly linked to increased risk of disease.

Transient Inhibition of the JAK/STAT Pathway Prevents B-ALL Development in Genetically Predisposed Mice.

Preventing development of childhood B-cell acute lymphoblastic leukemia (B-ALL), a disease with devastating effects, is a longstanding and unsolved challenge. Heterozygous germline alterations in the PAX5 gene can lead to B-ALL upon accumulation of secondary mutations affecting the JAK/STAT signaling pathway. Preclinical studies have shown that this malignant transformation occurs only under immune stress such as exposure to infectious pathogens. Here we show in Pax5+/- mice that transient, early-life administration of clinically relevant doses of ruxolitinib, a JAK1/2 inhibitor, significantly mitigates the risk of B-ALL following exposure to infection; 1 of 29 animals treated with ruxolitinib developed B-ALL versus 8 of 34 untreated mice. Ruxolitinib treatment preferentially targeted Pax5+/- versus wild-type B-cell progenitors and exerted unique effects on the Pax5+/- B-cell progenitor transcriptional program. These findings provide the first in vivo evidence for a potential strategy to prevent B-ALL development. SIGNIFICANCE: JAK/STAT inhibition suppresses tumorigenesis in a B-ALL-susceptible mouse model, presenting a novel approach to prevent B-ALL onset.

The Second Oncogenic Hit Determines the Cell Fate of ETV6-RUNX1 Positive Leukemia.

ETV6-RUNX1 is almost exclusively associated with childhood B-cell acute lymphoblastic leukemia (B-ALL), but the consequences of ETV6-RUNX1 expression on cell lineage decisions during B-cell leukemogenesis are completely unknown. Clinically silent ETV6-RUNX1 preleukemic clones are frequently found in neonatal cord blood, but few carriers develop B-ALL as a result of secondary genetic alterations. The understanding of the mechanisms underlying the first transforming steps could greatly advance the development of non-toxic prophylactic interventions. Using genetic lineage tracing, we examined the capacity of ETV6-RUNX1 to instruct a malignant phenotype in the hematopoietic lineage by cell-specific Cre-mediated activation of ETV6-RUNX1 from the endogenous Etv6 gene locus. Here we show that, while ETV6-RUNX1 has the propensity to trigger both T- and B-lymphoid malignancies, it is the second hit that determines tumor cell identity. To instigate leukemia, both oncogenic hits must place early in the development of hematopoietic/precursor cells, not in already committed B-cells. Depending on the nature of the second hit, the resulting B-ALLs presented distinct entities that were clearly separable based on their gene expression profiles. Our findings give a novel mechanistic insight into the early steps of ETV6-RUNX1+ B-ALL development and might have major implications for the potential development of ETV6-RUNX1+ B-ALL prevention strategies.

Juvenile myelomonocytic leukemia in CBL syndrome associated with germline splice-site mutations: Two case reports and a literature review.

The clinical and laboratory criteria for hemophagocytic lymphohistiocytosis should be taken into account during the juvenile myelomonocytic leukemia diagnosis, specifically in CBL syndrome, to reveal the presence of primary rather than secondary associated hemophagocytosis.

Helpful Criteria When Implementing NGS Panels in Childhood Lymphoblastic Leukemia.

The development of Next-Generation Sequencing (NGS) has provided useful diagnostic, prognostic, and therapeutic strategies for individualized management of B-cell precursor acute lymphoblastic leukemia (BCP-ALL) patients. Consequently, NGS is rapidly being established in clinical practice. However, the technology's complexity, bioinformatics analysis, and the different available options difficult a broad consensus between different laboratories in its daily routine introduction. This collaborative study among Spanish centers was aimed to assess the feasibility, pros, and cons of our customized panel and other commercial alternatives of NGS-targeted approaches. The custom panel was tested in three different sequencing centers. We used the same samples to assess other commercial panels (OncomineTM Childhood Cancer Research Assay; Archer®FusionPlex® ALL, and Human Comprehensive Cancer Panel GeneRead Panel v2®). Overall, the panels showed a good performance in different centers and platforms, but each NGS approach presented some issues, as well as pros and cons. Moreover, a previous consensus on the analysis and reporting following international guidelines would be preferable to improve the concordance in results among centers. Our study shows the challenges posed by NGS methodology and the need to consider several aspects of the chosen NGS-targeted approach and reach a consensus before implementing it in daily practice.

Hipoxemia como única manifestación de hemoglobinopatía estructural / Hypoxemia as the only manifestation of structural hemoglobinopathy

Las hemoglobinopatías son resultado de mutaciones en los genes responsables de la estructura molecular de la hemoglobina. Tienen una expresividad clínica muy variable: desde mínimamente sintomáticas a patología grave. Presentamos el caso de un niño de tres años ingresado por una neumonía atípica con hipoxemia que, tras 11 días de ingreso, mantiene saturaciones periféricas de oxígeno (SpO) de 92-94% sin otra sintomatología, exploración física y estudio cardiopulmonar normal. En el seguimiento ambulatorio persiste la desaturación periférica con gasometría y cooximetría arterial normal. El padre del paciente presenta los mismos hallazgos tanto en la pulsioximetría como en la gasometría arterial. Ante la sospecha de una hemoglobinopatía estructural se realiza estudio genético y electroforético detectándose la presencia de hemoglobina Arta

Structural hemoglobinopathies are the result of gene mutations that cause alterations in the molecular structure of hemoglobin. They have a very variable clinical expression: from minimally symptomatic to severe pathology. We present the case of a 3-year-old boy admitted for atypical pneumonia with hypoxemia who, after 11 days of admission, maintained peripheral oxygen saturations (SpO) of 92-94% without other symptoms, physical examination and normal cardiopulmonary study. In outpatient follow-up, peripheral desaturation persists with gasometry and normal arterial co-oxymetry. Patient's father with the same findings in pulse oximetry as in arterial blood gases. When a structural hemoglobinopathy was suspected, a genetic and electrophoretic study was performed, detecting the presence of hemoglobin Arta

Introducing high-throughput sequencing into mainstream genetic diagnosis practice in inherited platelet disorders.

Inherited platelet disorders are a heterogeneous group of rare diseases, caused by inherited defects in platelet production and/or function. Their genetic diagnosis would benefit clinical care, prognosis and preventative treatments. Until recently, this diagnosis has usually been performed via Sanger sequencing of a limited number of candidate genes. High-throughput sequencing is revolutionizing the genetic diagnosis of diseases, including bleeding disorders. We have designed a novel high-throughput sequencing platform to investigate the unknown molecular pathology in a cohort of 82 patients with inherited platelet disorders. Thirty-four (41.5%) patients presented with a phenotype strongly indicative of a particular type of platelet disorder. The other patients had clinical bleeding indicative of platelet dysfunction, but with no identifiable features. The high-throughput sequencing test enabled a molecular diagnosis in 70% of these patients. This sensitivity increased to 90% among patients suspected of having a defined platelet disorder. We found 57 different candidate variants in 28 genes, of which 70% had not previously been described. Following consensus guidelines, we qualified 68.4% and 26.3% of the candidate variants as being pathogenic and likely pathogenic, respectively. In addition to establishing definitive diagnoses of well-known inherited platelet disorders, high-throughput sequencing also identified rarer disorders such as sitosterolemia, filamin and actinin deficiencies, and G protein-coupled receptor defects. This included disease-causing variants in DIAPH1 (n=2) and RASGRP2 (n=3). Our study reinforces the feasibility of introducing high-throughput sequencing technology into the mainstream laboratory for the genetic diagnostic practice in inherited platelet disorders.

Mutations in TP53 and JAK2 are independent prognostic biomarkers in B-cell precursor acute lymphoblastic leukaemia.

BACKGROUND: In B-cell precursor acute lymphoblastic leukaemia (B-ALL), the identification of additional genetic alterations associated with poor prognosis is still of importance. We determined the frequency and prognostic impact of somatic mutations in children and adult cases with B-ALL treated with Spanish PETHEMA and SEHOP protocols. METHODS: Mutational status of hotspot regions of TP53, JAK2, PAX5, LEF1, CRLF2 and IL7R genes was determined by next-generation deep sequencing in 340 B-ALL patients (211 children and 129 adults). The associations between mutation status and clinicopathological features at the time of diagnosis, treatment outcome and survival were assessed. Univariate and multivariate survival analyses were performed to identify independent prognostic factors associated with overall survival (OS), event-free survival (EFS) and relapse rate (RR). RESULTS: A mutation rate of 12.4% was identified. The frequency of adult mutations was higher (20.2% vs 7.6%, P=0.001). TP53 was the most frequently mutated gene (4.1%), followed by JAK2 (3.8%), CRLF2 (2.9%), PAX5 (2.4%), LEF1 (0.6%) and IL7R (0.3%). All mutations were observed in B-ALL without ETV6-RUNX1 (P=0.047) or BCR-ABL1 fusions (P<0.0001). In children, TP53mut was associated with lower OS (5-year OS: 50% vs 86%, P=0.002) and EFS rates (5-year EFS: 50% vs 78.3%, P=0.009) and higher RR (5-year RR: 33.3% vs 18.6% P=0.037), and was independently associated with higher RR (hazard ratio (HR)=4.5; P=0.04). In adults, TP53mut was associated with a lower OS (5-year OS: 0% vs 43.3%, P=0.019) and a higher RR (5-year RR: 100% vs 61.4%, P=0.029), whereas JAK2mut was associated with a lower EFS (5-year EFS: 0% vs 30.6%, P=0.035) and a higher RR (5-year RR: 100% vs 60.4%, P=0.002). TP53mut was an independent risk factor for shorter OS (HR=2.3; P=0.035) and, together with JAK2mut, also were independent markers of poor prognosis for RR (TP53mut: HR=5.9; P=0.027 and JAK2mut: HR=5.6; P=0.036). CONCLUSIONS: TP53mut and JAK2mut are potential biomarkers associated with poor prognosis in B-ALL patients.

Application of a molecular diagnostic algorithm for haemophilia A and B using next-generation sequencing of entire F8, F9 and VWF genes.

Currently, molecular diagnosis of haemophilia A and B (HA and HB) highlights the excess risk-inhibitor development associated with specific mutations, and enables carrier testing of female relatives and prenatal or preimplantation genetic diagnosis. Molecular testing for HA also helps distinguish it from von Willebrand disease (VWD). Next-generation sequencing (NGS) allows simultaneous investigation of several complete genes, even though they may span very extensive regions. This study aimed to evaluate the usefulness of a molecular algorithm employing an NGS approach for sequencing the complete F8, F9 and VWF genes. The proposed algorithm includes the detection of inversions of introns 1 and 22, an NGS custom panel (the entire F8, F9 and VWF genes), and multiplex ligation-dependent probe amplification (MLPA) analysis. A total of 102 samples (97 FVIII- and FIX-deficient patients, and five female carriers) were studied. IVS-22 screening identified 11 out of 20 severe HA patients and one female carrier. IVS-1 analysis did not reveal any alterations. The NGS approach gave positive results in 88 cases, allowing the differential diagnosis of mild/moderate HA and VWD in eight cases. MLPA confirmed one large exon deletion. Only one case did have no pathogenic variants. The proposed algorithm had an overall success rate of 99 %. In conclusion, our evaluation demonstrates that this algorithm can reliably identify pathogenic variants and diagnose patients with HA, HB or VWD.

Wiskott-Aldrich syndrome in a child presenting with macrothrombocytopenia.

Wiskott-Aldrich syndrome (WAS) is a rare X-linked recessive disease resulting from variants in the WAS gene, characterized by a triad of immunodeficiency, eczema, and thrombocytopenia. Despite the fact that WAS is traditionally differentiated from immune thrombocytopenia (ITP) by small size of WAS platelets, in practice, microthrombocytopenia may occasionally not be present, and in certain cases, WAS patients exhibit some parallelism to ITP patients. We characterized one patient presenting with the classic form of the disease but increased mean platelet volume. Molecular studies revealed a novel hemizygous 1-bp deletion in WAS gene, c.802delC, leading to a frameshift and stop codon at amino acid 308 (p.Arg268Glyfs*40). Next-generation sequencing of a total of 70 additional genes known to harbor variants implicated in inherited platelet disorders did not identify additional defects. The pathogenesis of macrothrombocytopenia in this case is not known, but probably the coexistence of a still unidentified additional genetic variant might be involved.

Genome-Wide DNA Copy Number Analysis of Acute Lymphoblastic Leukemia Identifies New Genetic Markers Associated with Clinical Outcome.

UNLABELLED: Identifying additional genetic alterations associated with poor prognosis in acute lymphoblastic leukemia (ALL) is still a challenge. AIMS: To characterize the presence of additional DNA copy number alterations (CNAs) in children and adults with ALL by whole-genome oligonucleotide array (aCGH) analysis, and to identify their associations with clinical features and outcome. Array-CGH was carried out in 265 newly diagnosed ALLs (142 children and 123 adults). The NimbleGen CGH 12x135K array (Roche) was used to analyze genetic gains and losses. CNAs were analyzed with GISTIC and aCGHweb software. Clinical and biological variables were analyzed. Three of the patients showed chromothripsis (cth6, cth14q and cth15q). CNAs were associated with age, phenotype, genetic subtype and overall survival (OS). In the whole cohort of children, the losses on 14q32.33 (p = 0.019) and 15q13.2 (p = 0.04) were related to shorter OS. In the group of children without good- or poor-risk cytogenetics, the gain on 1p36.11 was a prognostic marker independently associated with shorter OS. In adults, the gains on 19q13.2 (p = 0.001) and Xp21.1 (p = 0.029), and the loss of 17p (p = 0.014) were independent markers of poor prognosis with respect to OS. In summary, CNAs are frequent in ALL and are associated with clinical parameters and survival. Genome-wide DNA copy number analysis allows the identification of genetic markers that predict clinical outcome, suggesting that detection of these genetic lesions will be useful in the management of patients newly diagnosed with ALL.

Increasing incidence of invasive aspergillosis in pediatric hematology oncology patients over the last decade: a retrospective single centre study.

There is scanty information about invasive aspergillosis (IA) in the pediatric population. A review of IA at Hospital Infantil Universitario Niño Jesús between 1996 and 2006 was undertaken to analyze incidence, risk factors, and treatment response. Twenty patients were diagnosed with probable or proven IA during the study period, with a cumulative incidence of 1.96%. Incidence was higher in hematopoietic stem cell transplantation (HSCT) recipients: 2.26% (3.5% in allogeneic HSCT and 1.2% in autologous HSCT). A significative increase in IA incidence was observed along the study period (P=0.013), although this increase did not reach signification if only proven cases were compared (P=0.058). Most patients presented multiple risk factors for IA (87% more than 1, and 47% more than 3). The most frequently described risk factor was chemotherapy (90%), after by long-term neutropenia (90%), and corticotherapy (75%). Main locations of the infection were pulmonary (8 patients), cutaneous (3 patients) and intestinal (3 patients). Six patients presented disseminated IA. Initial response to treatment was 55%, although 3 of these cases had a subsequent episode. Global antifungal response, at the end of the follow-up, was 45%. IA-related mortality was 55%. Global mortality was 90%. Only 2 patients (isolated cutaneous IA cases) survived. Seven patients died due to their underlying malignant disease without active fungal disease. Incidence of IA in oncology children is increasing, and in adults. In our experience, IA is a marker of poor outcome even for patients who initially respond to antifungal treatment.

Utilidad del dímero D como marcador analítico en urgencias pediátricas / Utility of D-dimer level as an analytical marker in pediatric emergencies

Objetivos: Describir nuestra experiencia acerca del uso del dímero D (DD) en urgencias pediátricas. Método: Se realiza un estudio descriptivo, retrospectivo. Revisamos todas las historias clínicas de urgencias de nuestro centro en las que se realizó determinación analítica de lDD durante los años 2005 y 2006. Describimos los datos obtenidos y analizamos estadísticamente la asociación del DD con un parámetro de respuesta inflamatoria (la proteína C reactiva) mediante un estudio de correlación no paramétrico. Resultados: Los principales motivos de consulta, en las 137 historias revisadas, fueron exantema y fiebre. El DD resultó positivo en el 34,3% de los casos. No se halló correlación estadísticamente significativa entre el DD y la proteína C reactiva. El DD fue positivo en el 71% de los casos de sepsis. Conclusiones: El DD se eleva en algunos procesos inflamatorios, de manera inespecífica. Su interpretación es difícil y puede llevar a confusión. Es necesario analizarlo en su contexto clínico (AU)

Objectives: To describe our experience using D-dimer levels in attending pediatric emergencies. Methods: For this retrospective descriptive study we reviewed all emergency patient records in which D-dimer levels were measured in 2005 and 2006. We compiled descriptive statistics and analyzed the association between levels of Ddimer and C-reactive protein (as a marker of inflammatory response) using a nonparametric correlation test. Results: Rash and fever were the main reasons for attending the emergency room. The D-dimer level was elevated in34.3% of the cases. D-dimer and C-reactive protein levels were not correlated. The D-dimer level was elevated in 71% of the patients with sepsis. Conclusions: D-dimer elevation is a nonspecific marker in certain inflammatory processes. It is difficult to interpret, may lead to confusion, and should be read in a manner that is consistent with the clinical context. Prospective studies are needed to provide evidence of its utility as a marker in acute conditions in children (AU)