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XMEN disease (X-linked immunodeficiency with magnesium defect, EBV infection, and neoplasia) is a rare Inborn Error of Immunity (IEI)characterized by impaired magnesium ion transport due to mutations in the MAGT1 gene, which subsequently affects immune cell function. Timely diagnosis and prompt intervention are essential for improving patient outcomes. Allogeneic hematopoietic stem cell transplantation (HSCT) offers a potential therapeutic approach to restore MAGT1 function. We report an infant with XMEN who acquired a novel mutation in the MAGT1 gene, presenting recurrent severe skin infections and neutropenia after 6 months of age, which was effectively managed following aggressive anti-infective treatment and HSCT.

Background Selective anti-polysaccharide antibody deficiency (SPAD) with CD5 B-cell predominance and autoimmune phenomena was identified in a male cohort first reported by Antall et al in 1999. The phenotypically likewise and genotypically identical X-linked immunodeficiency with magnesium defect, Epstein–Barr Virus infection, and neoplasia (XMEN) disease was defined as a novel primary immunodeficiency (PID) in 2011. Recent studies of the magnesium transporter 1 (MAGT1) gene mutation reveal glycosylation defects contributing to more phenotypic variance than the “XMEN” title pathologies. The updated title, “X-linked MAGT1 deficiency with increased susceptibility to EBV-infection and N-linked glycosylation defect,” was proposed in 2020. Objectives To reflect the patient population more accurately, a prospective classification update may consider MAGT1 glycobiological errors contributing to phenotypic variance but also pre-genetic testing era reports with CD5 B-cell predominance. Methods Patient 1 from Antall et al presented at 28 years of age for further immunological evaluation of his CD5/CD19 B-cell predominance diagnosed at 5 years old. Design Immune re-evaluation done through flow cytometry and next-generation sequencing. Results Flow cytometry B-cell phenotyping revealed persistent CD5+CD19+ (93%). Flow cytometric histogram quantified reduced activator CD16+CD56+ natural killer and CD8+ T-cell receptor, Group 2, Member D (NKG2D) glycoprotein expression. A c.923-1_934 deletion loss of function mutation was identified in the MAGT1 gene. Conclusion We suggest the novel PID XMEN, based on its CD5 B-cell predominance, had been discovered and reported over a decade earlier as CD5+ PID based on the MAGT1 mutation found in the same. We encourage consideration of combining these labels and recent findings to offer the most accurate classification of this disease.