[Clinical analysis of 9 children of B-cell acute lymphoblastic leukemia with MEF2D gene rearrangement]

Objective: To summarize the clinical characteristics, molecular genetic features, diagnosis and treatment of pediatric B-cell acute lymphoblastic leukemia (B-ALL) with myocyte enhancer factor 2D (MEF2D) gene rearrangement. Methods: In this case series study, clinical data of 9 children newly diagnosed B-ALL with MEF2D gene rearranged, admitted to the First Affiliated Hospital of Zhengzhou University from May 2020 to June 2025 were collected. The clinical characteristics, laboratory findings, treatment regimens, and outcomes of these patients were systematically analyzed. Results: A total of 9 chlidren were enrolled (3 boys and 6 girls), with the diagnostic age of 12.0 (11.0, 13.8) years. Five children initially presented with fever accompanied by arthralgia. Immunophenotyping revealed that 1 child was early precursor B-ALL and the remaining 8 children were common B-ALL. Uniformly high expression of CD38 and absence of cytoplasmic immunoglobulin M (cIgM) expression in all 9 children. Bone marrow smear examination demonstrated cytoplasmic vacuolization in 5 children. RNA sequencing detected 5 types of MEF2D gene fusion partners, including BCL9 gene in 4 children, FOXJ2 gene in 2 children, and 1 child each of DAZAP1 gene, SS18 gene, and ARNT gene. Heterozygous deletions of CDKN2A or CDKN2B gene were detected in 6 children, and 8 children exhibited concurrent gene variations. Induction therapy with the vincristine+daunorubicin+L-asparaginase+prednisone (VDLP) regimen was administered to all 9 children in accordance with＂the Clinical Practice Guideline for Childhood Acute Lymphoblastic Leukemia (2018)＂. At the end of induction remission therapy, minimal residual disease (MRD) assessed by flow cytometry were all negative (<0.01%) in all cases. One child was lost to follow-up during the maintenance phase. Three children experienced relapse and succumbed. The remaining 5 children were followed up until October 10, 2025, with 2 in disease-free survival and 3 still receiving regular treatment. Conclusions: B-ALL with MEF2D gene rearrangement predominantly affects older children, typically presenting with fever accompanied by arthralgia. This subtype exhibits high CD38 expression and absence of cIgM expression, with a frequent incidence of CDKN2A or CDKN2B gene deletions. Although the initial treatment response was good, the risk of recurrence was high and the efficacy of salvage treatment was limited. For this high-risk sub-type, the use of next-generation sequencing for MRD monitoring could be explored to more accurately assess the risk of relapse.