Clinical and molecular characteristics of MEF2D fusion-positive B-cell precursor 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.

A 6-year-old girl diagnosed with mevalonate kinase deficiency who had hydrops fetalis and neonatal-onset cholestasis.

We experienced a 6-year-old girl diagnosed with mevalonate kinase deficiency (MKD) who had cholestasis, anemia, and elevated inflammatory markers in neonatal period. She was admitted to our hospital because of fever and elevated inflammatory markers at 5 years 11months of age. Without using antibiotics, the fever and the inflammatory markers were spontaneously resolved. MKD was suspected from elevated serum IgD level and the recurrent febrile attacks. The genetic test revealed heterozygous mutation of p.Leu51Phe known as causative gene of MKD and p.Met 282Thr which is the novel mutation. In addition, urinary mevalonate levels increased both in afebrile and febrile periods, and mevalonate kinase activity level was very low. Prednisolone was administered on each attack, and her febrile attack has been controlled well since she was diagnosed with MKD. Fetal edema, cholestasis, anemia, elevation of inflammatory markers in her neonatal period are considered to be complications of MKD. Recurrent fever attacks compromise quality of life in patients with MKD. Children with unexplained cholestasis and anemia in neonatal period, or recurrent fever attacks with elevated inflammatory markers should be examined for MKD.

H1N1 influenza (swine flu)-associated thrombotic microangiopathy with a markedly high plasma ratio of von Willebrand factor to ADAMTS13.

We describe an 18-year-old woman infected with H1N1 influenza followed by thrombotic microangiopathy. During the acute phase, her plasma levels of von Willebrand factor (VWF) were remarkably elevated, whereas those of ADAMTS13 were reduced without its inhibitors, generating a markedly high ratio of VWF to ADAMTS13 in circulation. A retrospective analysis established the following hypothesis: an influenza-mediated cytokine storm induced an enhanced release of unusually large VWF multimers (UL-VWFM) from vascular endothelial cells, generating platelet thrombi in microcirculatures under high shear stress. Plasma exchange removed UL-VWFM and cytokines, and rescued her life. This report sheds a light on a hitherto unrecognized influenza complication.