Shinsuke Hirabayashi

Prevalence, clinical characteristics, and prognosis of GATA2-related myelodysplastic syndromes in children and adolescents

Germline GATA2 mutations cause cellular deficiencies with high propensity for myeloid disease. We investigated 426 children and adolescents with primary myelodysplastic syndrome (MDS) and 82 cases with secondary MDS enrolled in 2 consecutive prospective studies of the European Working Group of MDS in Childhood (EWOG-MDS) conducted in Germany over a period of 15 years. Germline GATA2 mutations accounted for 15% of advanced and 7% of all primary MDS cases, but were absent in children with MDS secondary to therapy or acquired aplastic anemia. Mutation carriers were older at diagnosis and more likely to present with monosomy 7 and advanced disease compared with wild-type cases. For stratified analysis according to karyotype, 108 additional primary MDS patients registered with EWOG-MDS were studied. Overall, we identified 57 MDS patients with germline GATA2 mutations. GATA2 mutations were highly prevalent among patients with monosomy 7 (37%, all ages) reaching its peak in adolescence (72% of adolescents with monosomy 7). Unexpectedly, monocytosis was more frequent in GATA2-mutated patients. However, when adjusted for the selection bias from monosomy 7, mutational status had no effect on the hematologic phenotype. Finally, overall survival and outcome of hematopoietic stem cell transplantation (HSCT) were not influenced by mutational status. This study identifies GATA2 mutations as the most common germline defect predisposing to pediatric MDS with a very high prevalence in adolescents with monosomy 7. GATA2 mutations do not confer poor prognosis in childhood MDS. However, the high risk for progression to advanced disease must guide decision-making toward timely HSCT.

Spliceosomal gene aberrations are rare, coexist with oncogenic mutations, and are unlikely to exert a driver effect in childhood MDS and JMML

Somatic mutations of the spliceosomal machinery occur frequently in adult patients with myelodysplastic syndrome (MDS). We resequenced SF3B1, U2AF35, and SRSF2 in 371 children with MDS or juvenile myelomonocytic leukemia. We found missense mutations in 2 juvenile myelomonocytic leukemia cases and in 1 child with systemic mastocytosis with MDS. In 1 juvenile myelomonocytic leukemia patient, the SRSF2 mutation that initially coexisted with an oncogenic NRAS mutation was absent at relapse, whereas the NRAS mutation persisted and a second, concomitant NRAS mutation later emerged. The patient with systemic mastocytosis and MDS carried both mutated U2AF35 and KIT in a single clone as confirmed by clonal sequencing. In the adult MDS patients sequenced for control purposes, we detected previously reported mutations in 7/30 and a novel SRSF2 deletion (c.284_307del) in 3 of 30 patients. These findings implicate that spliceosome mutations are rare in pediatric MDS and juvenile myelomonocytic leukemia and are unlikely to operate as driver mutations.

ZNF384-related fusion genes define a subgroup of childhood B-cell precursor acute lymphoblastic leukemia with a characteristic immunotype

Fusion genes involving ZNF384 have recently been identified in B-cell precursor acute lymphoblastic leukemia, and 7 fusion partners have been reported. We further characterized this type of fusion gene by whole transcriptome sequencing and/or polymerase chain reaction. In addition to previously reported genes, we identified BMP2K as a novel fusion partner for ZNF384. Including the EP300-ZNF384 that we reported recently, the total frequency of ZNF384-related fusion genes was 4.1% in 291 B-cell precursor acute lymphoblastic leukemia patients enrolled in a single clinical trial, and TCF3-ZNF384 was the most recurrent, with a frequency of 2.4%. The characteristic immunophenotype of weak CD10 and aberrant CD13 and/or CD33 expression was revealed to be a common feature of the leukemic cells harboring ZNF384-related fusion genes. The signature gene expression profile in TCF3-ZNF384-positive patients was enriched in hematopoietic stem cell features and related to that of EP300-ZNF384-positive patients, but was significantly distinct from that of TCF3-PBX1-positive and ZNF384-fusion-negative patients. However, clinical features of TCF3-ZNF384-positive patients are markedly different from those of EP300-ZNF384-positive patients, exhibiting higher cell counts and a younger age at presentation. TCF3-ZNF384-positive patients revealed a significantly poorer steroid response and a higher frequency of relapse, and the additional activating mutations in RAS signaling pathway genes were detected by whole exome analysis in some of the cases. Our observations indicate that ZNF384-related fusion genes consist of a distinct subgroup of B-cell precursor acute lymphoblastic leukemia with a characteristic immunophenotype, while the clinical features depend on the functional properties of individual fusion partners.

Mutational landscape in children with myelodysplastic syndromes is distinct from adults: specific somatic drivers and novel germline variants

Mutational landscape in children with myelodysplastic syndromes is distinct from adults: specific somatic drivers and novel germline variants

Clinical characteristics and treatment outcome in 65 cases with refractory cytopenia of childhood defined according to the WHO 2008 classification

This study analysed 65 children who were prospectively registered between 1999 and 2008 and fulfilled the World Health Organization 2008 criteria of refractory cytopenia of childhood (RCC). First‐line therapy was determined by the treating physicians: 25 patients received immunosuppressive therapy (IST), 12 patients received haematopoietic stem cell transplantation (HSCT) and one patient received intensive chemotherapy. The remaining 27 patients were followed without treatment for more than 2 years (watch and wait; WW). In the WW group, 18 patients had stable disease without further intervention. Thirteen of 29 patients (45%) who ended up receiving IST showed response. The combination of ciclosporin and antithymocyte globulin was not shown to be superior to ciclosporin alone with regard to response rate or survival. Of 28 patients who ended up undergoing HSCT, 17 patients are alive in complete remission, whereas nine patients died mostly due to transplantation‐related mortality. The 5‐year overall survival for all patients was 82 ± 5%. Eight patients suffered from disease progression. Patients with monosomy 7 or multilineage‐dysplasia had a significantly higher incidence of disease progression. This analysis revealed heterogeneity in the clinical course of RCC, varying from those who remained stable for long periods to those who progressed to advanced disease.

The ex vivo production of ammonia predicts L-asparaginase biological activity in children with acute lymphoblastic leukemia

Patients with acute lymphoblastic leukemia (ALL), who develop antiasparaginase antibodies without clinical allergic reactions (“silent inactivation”) during l-asparaginase (l-Asp) treatment, have poor outcomes. Ammonia is produced by hydrolysis of asparagine by l-Asp. We postulated that plasma ammonia level might reflect the biological activity of l-Asp. Five children with ALL treated according to the Tokyo Children’s Cancer Study Group (TCCSG) protocol were enrolled. Plasma ammonia levels were analyzed immediately and 1 h after incubation at room temperature and “ex vivo ammonia production” was defined as increase in ammonia concentration. Ex vivo ammonia production well correlated with l-Asp activity (r = 0.882, P < 0.01, n = 23). It always exceeded 170 μg/dL (170–345 μg/dL) in induction therapy. We found 3 patients whose ammonia production was negligible during later phases of therapy. Antiasparaginase antibody was detected and l-Asp activity decreased in these patients. Ex vivo ammonia production is a surrogate marker of l-Asp biological activity.

Heterogeneity of GATA2-related myeloid neoplasms

The GATA2 gene codes for a master hematopoietic transcription factor that is essential for the proliferation and maintenance of hematopoietic stem and progenitor cells. Heterozygous germline mutations in GATA2 have been initially associated with several clinical entities that are now collectively defined as GATA2 deficiency. Despite pleiotropic clinical manifestations, the high propensity for the development of myelodysplastic syndromes (MDS) constitutes the most common clinical denominator of this major MDS predisposition syndrome. The immunological phenotypes can be variable and mostly include deficiency of monocytes and/or B cells. Thus far, nearly 380 GATA2-deficient patients had been reported, with a roughly estimated prevalence of myeloid neoplasia of at least 75%. The most common abnormal karyotypes associated with GATA2-related MDS are monosomy 7, der(1;7) and trisomy 8. The overall clinical penetrance seems to be nearly complete for this transcriptopathy disorder. The high-risk MDS subtypes and karyotypes, and the underlying immunodeficiency guide decision-making toward timely stem cell transplantation.

Constitutional abnormalities of IDH1 combined with secondary mutations predispose a patient with Maffucci syndrome to acute lymphoblastic leukemia

Maffucci syndrome is a nonhereditary disorder caused by somatic mosaic isocitrate dehydrogenase 1 or 2 (IDH1 or IDH2) mutations and is characterized by multiple enchondromas along with hemangiomas. Malignant transformation of enchondromas to chondrosarcomas and secondary neoplasms, such as brain tumors or acute myeloid leukemia, are serious complications. A 15‐year‐old female with Maffucci syndrome developed B‐cell precursor acute lymphoblastic leukemia (BCP‐ALL). A somatic mutation in IDH1 was detected in hemangioma and leukemic cells. KRAS mutation and deletion of IKZF1 were detected in leukemic cells. Patients with Maffucci syndrome may, therefore, be at risk of BCP‐ALL associated with secondary genetic events that affect lymphocyte differentiation.

Clinical and Molecular Heterogeneity of RTEL1 Deficiency

Typical features of dyskeratosis congenita (DC) resulting from excessive telomere shortening include bone marrow failure (BMF), mucosal fragility, and pulmonary or liver fibrosis. In more severe cases, immune deficiency and recurring infections can add to disease severity. RTEL1 deficiency has recently been described as a major genetic etiology, but the molecular basis and clinical consequences of RTEL1-associated DC are incompletely characterized. We report our observations in a cohort of six patients: five with novel biallelic RTEL1 mutations p.Trp456Cys, p.Ile425Thr, p.Cys1244ProfsX17, p.Pro884_Gln885ins53X13, and one with novel heterozygous mutation p.Val796AlafsX4. The most unifying features were hypocellular BMF in 6/6 and B-/NK-cell lymphopenia in 5/6 patients. In addition, three patients with homozygous mutations p.Trp456Cys or p.Ile425Thr also suffered from immunodeficiency, cerebellar hypoplasia, and enteropathy, consistent with Hoyeraal-Hreidarsson syndrome. Chromosomal breakage resembling a homologous recombination defect was detected in patient-derived fibroblasts but not in hematopoietic compartment. Notably, in both cellular compartments, differential expression of 1243aa and 1219/1300aa RTEL1 isoforms was observed. In fibroblasts, response to ionizing irradiation and non-homologous end joining were not impaired. Telomeric circles did not accumulate in patient-derived primary cells and lymphoblastoid cell lines, implying alternative pathomechanisms for telomeric loss. Overall, RTEL1-deficient cells exhibited a phenotype of replicative exhaustion, spontaneous apoptosis and senescence. Specifically, CD34+ cells failed to expand in vitro, B-cell development was compromised, and T-cells did not proliferate in long-term culture. Finally, we report on the natural history and outcome of our patients. While two patients died from infections, hematopoietic stem cell transplantation (HSCT) resulted in sustained engraftment in two patients. Whether chemotherapy negatively impacts on the course and onset of other DC-related symptoms remains open at present. Early-onset lung disease occurred in one of our patients after HSCT. In conclusion, RTEL deficiency can show a heterogeneous clinical picture ranging from mild hypocellular BMF with B/NK cell lymphopenia to early-onset, very severe, and rapidly progressing cellular deficiency.

Clinical and molecular characteristics of MEF2D fusion-positive precursor B-cell acute lymphoblastic leukemia in childhood, including a novel translocation resulting in MEF2D-HNRNPH1 gene fusion

Fusion genes involving MEF2D have recently been identified in precursor B-cell acute lymphoblastic leukemia, mutually exclusive of the common risk stratifying genetic abnormalities, although their true incidence and associated clinical characteristics remain unknown. We identified 16 cases of acute lymphoblastic leukemia and 1 of lymphoma harboring MEF2D fusions, including MEF2D-BCL9 (n=10), MEF2D-HNRNPUL1 (n=6), and one novel MEF2D-HNRNPH1 fusion. The incidence of MEF2D fusions overall was 2.4% among consecutive precursor B-cell acute lymphoblastic leukemia patients enrolled onto a single clinical trial. They frequently showed a cytoplasmic μ chain-positive pre-B immunophenotype, and often expressed an aberrant CD5 antigen. Besides up- and down-regulation of HDAC9 and MEF2C, elevated GATA3 expression was also a characteristic feature of MEF2D fusion-positive patients. Mutations of PHF6, recurrent in T-cell acute lymphoblastic leukemia, also showed an unexpectedly high frequency (50%) in these patients. MEF2D fusion-positive patients were older (median age 9 years) with elevated WBC counts (median: 27,300/ml) at presentation and, as a result, were mostly classified as NCI high risk. Although they responded well to steroid treatment, MEF2D fusion-positive patients showed a significantly worse outcome, with 53.3% relapse and subsequent death. Stem cell transplantation was ineffective as salvage therapy. Interestingly, relapse was frequently associated with the presence of CDKN2A/CDKN2B gene deletions. Our observations indicate that MEF2D fusions comprise a distinct subgroup of precursor B-cell acute lymphoblastic leukemia with a characteristic immunophenotype and gene expression signature, associated with distinct clinical features.