Rationale: The rare t(3;21)(q26;q22) translocation results in gene fusion and generates multiple fusion transcripts, which are typically associated with therapy-related myelodysplastic syndrome, acute myeloid leukemia, and chronic myelogenous leukemia. Here, we report a rare case of de novo acute myelomonocytic leukemia in a young child with t(3;21)(q26;q22). Patient concerns: A 2-and-a-half-year-old female patient presented with abdominal pain, cough, paleness, and fever for 3 weeks, without any history of malignant diseases. Diagnoses: Chest computed tomography revealed pneumonia. Bone marrow smear confirmed acute myelomonocytic leukemia. Cytogenetic analysis and Sanger sequencing identified RUNX1-MECOM and RUNX1-RPL22 fusion genes as a result of t(3;21)(q26;q22). Interventions: The patient received 3 courses of chemotherapy, but bone marrow smear examination showed no remission. According to the wishes of the patient family, the allogeneic hematopoietic stem cell transplantation (Allo-HSCT) was chosen. Outcomes: The patient did not experience any adverse reactions after Allo-HSCT. The red blood cells and platelets increased without transfusion. The pneumonia recovered after antibiotic treatment. Lessons: The patient recovered well after Allo-HSCT. Therefore, for patients with RUNX1-MECOM and RUNX1-RPL22 fusion genes, transplantation may be a good choice when chemotherapy is not effective.

Rationale: Bone marrow transplantation (BMT) is an established therapy for hematological malignancies. In recent years, with the advancement of medical research, evaluating the efficacy of BMT in recipients by detecting the presence or absence of chromosomes from an opposite-sex donor has been widely recognized. Numerous cases have shown that the sex hormone levels of recipients who receive BMT from the opposite sex will change significantly. However, whether such hormonal changes will impair sexual function or lead to physiological sex-related manifestations, or even cause changes in the biological sex of BMT recipients, these questions make people cannot help but think deeply. Herein, we report a case of a male patient who received allogeneic BMT from a female donor, demonstrating that transplantation only replaced the recipient’s hematopoietic stem cells and did not change the patient’s biological sex. Patient concerns: We report a 22-year-old male who was diagnosed with azoospermia during a recent physical examination and sought medical attention at our hospital. Diagnoses: Semen examination showed no sperm, and the analysis of the peripheral blood chromosome karyotype is 46,XX. The preliminary clinical diagnosis is azoospermia with sexual dysfunction. Interventions: The results of Y-chromosome microdeletion in peripheral blood could not be interpreted. After reviewing the patient’s history, we only found that he had received a BMT from an opposite-sex donor for chronic myelocytic leukemia 14 years ago, when he was only 8 years old. The peripheral blood and buccal mucosal swabs were collected for Y-chromosome microdeletion examination again. At this point, the truth has finally come to light: At this point, the etiology became clear: The patient’s peripheral blood showed chimeric DNA from both the BMT donor and recipient, while the buccal mucosal swabs—originating from embryonic development—accurately reflected his pretransplantation genetic profile. Outcomes: The patient, being only 22 years old and having no intention of getting pregnant at present, received no further medical treatment. Lessons: This case report demonstrates that while sex-mismatched BMT may alter secondary sexual characteristics, it does not fundamentally change the recipient’s genetic sex or core gender identity.

Rationale: Murine typhus, caused by Rickettsia typhi , is a globally distributed flea-borne rickettsiosis. Although rarely recognized, it can trigger hemophagocytic lymphohistiocytosis (HLH), a life-threatening hyperinflammatory syndrome. Nonspecific febrile illness and atypical petechial eruptions frequently lead to delayed or missed diagnoses. This report aims to illustrate the diagnostic process and clinical implications of murine typhus-associated HLH in a pediatric patient, and to evaluate the utility of metagenomic next-generation sequencing (mNGS) as an unbiased detection tool for occult pathogens. Patient concerns: A 10-year-old child was admitted with unexplained recurrent fever and generalized petechiae, refractory to treatment at outside hospitals. Diagnoses: The patient was ultimately diagnosed with murine typhus-associated HLH caused by R typhi , based on a comprehensive diagnostic work-up. Interventions: Empirical dexamethasone was initiated promptly to control hyperinflammation. After mNGS confirmation, oral doxycycline was added for targeted anti-rickettsial therapy. Outcomes: The patient’s clinical status continued to improve, culminating in discharge. Lessons: Murine typhus-associated HLH should be considered in febrile children with unexplained cytopenias and petechiae. Early empiric HLH-directed immunosuppression followed by pathogen-specific therapy improves prognosis. mNGS provides a rapid, unbiased method to detect rare, overlooked pathogens and guide definitive treatment when conventional tests are negative.

Atypical Hand-foot-mouth disease (HFMD), which is caused predominantly by enteroviruses (EVs) shares overlapping cutaneous manifestations with varicella, a condition triggered by varicella-zoster virus (VZV) and further complicates diagnosis. This study systematically characterized the clinical features, hematological profiles, and infection patterns (single, mixed and sequential infection) of pediatric patients with poorly distinguishable EV and VZV infection to improve diagnostic accuracy and optimize clinical management strategies. A retrospective analysis was conducted on the cases that were difficult to distinguish and were confirmed by polymerase chain reaction (PCR) from 2021 to 2025, including demographics, symptoms, hematological profiles, and infection patterns. Among the 85 patients, 33 had a single EV infection and 46 had a single VZV infection, with 4 mixed infections and 2 sequential infections. Compared with patients in the VZV group, those in the EV group were more often associated with local rashes on the limbs and around the mouth, often accompanied by oral vesicles. In contrast, patients with VZV infection usually exhibited pruritic, widespread skin rashes across the body. Virological testing identified CV-A6 as the dominant EV serotype (51.52%). Hematological profiles revealed increased atypical lymphocytes in patients with VZV infection compared with those with EV infection. Patients with mixed infection maybe correlated with more extensive skin lesions. The clinical differentiation of poorly distinguishable EV and VZV infection presents significant challenges, especially in children with mixed infection or atypical features. In the absence of early virological testing, it is hoped that this study can provide some guidance for the diagnosis of HFMD and chickenpox that are difficult to distinguish or have mixed infection.