A Double-Blind, Placebo-Controlled, Crossover Study of Magnesium Supplementation in Patients with XMEN Disease.

X-linked MAGT1 deficiency with increased susceptibility to Epstein-Barr virus (EBV) infection and N-linked glycosylation defect (XMEN) disease is an inborn error of immunity caused by loss-of-function mutations in the magnesium transporter 1 (MAGT1) gene. The original studies of XMEN patients focused on impaired magnesium regulation, leading to decreased EBV-cytotoxicity and the loss of surface expression of the activating receptor "natural killer group 2D" (NKG2D) on CD8+ T cells and NK cells. In vitro studies showed that supraphysiological supplementation of magnesium rescued these defects. Observational studies in 2 patients suggested oral magnesium supplementation could decrease EBV viremia. Hence, we performed a randomized, double-blind, placebo-controlled, crossover study in 2 parts. In part 1, patients received either oral magnesium L-threonate (MLT) or placebo for 12 weeks followed by 12 weeks of the other treatment. Part 2 began with 3 days of high-dose intravenous (IV) magnesium sulfate (MgSO4) followed by open-label MLT for 24 weeks. One EBV-infected and 3 EBV-naïve patients completed part 1. One EBV-naïve patient was removed from part 2 of the study due to asymptomatic elevation of liver enzymes during IV MgSO4. No change in EBV or NKG2D status was observed. In vitro magnesium supplementation experiments in cells from 14 XMEN patients failed to significantly rescue NKG2D expression and the clinical trial was stopped. Although small, this study indicates magnesium supplementation is unlikely to be an effective therapeutic option in XMEN disease.

An Update on XMEN Disease.

"X-linked immunodeficiency with magnesium defect, Epstein-Barr virus (EBV) infection, and neoplasia" (XMEN) disease is an inborn error of glycosylation and immunity caused by loss of function mutations in the magnesium transporter 1 (MAGT1) gene. It is a multisystem disease that strongly affects certain immune cells. MAGT1 is now confirmed as a non-catalytic subunit of the oligosaccharyltransferase complex and facilitates Asparagine (N)-linked glycosylation of specific substrates, making XMEN a congenital disorder of glycosylation manifesting as a combined immune deficiency. The clinical disease has variable expressivity, and impaired glycosylation of key MAGT1-dependent glycoproteins in addition to Mg2+ abnormalities can explain some of the immune manifestations. NKG2D, an activating receptor critical for cytotoxic function against EBV, is poorly glycosylated and invariably decreased on CD8+ T cells and natural killer (NK) cells from XMEN patients. It is the best biomarker of the disease. The characterization of EBV-naïve XMEN patients has clarified features of the genetic disease that were previously attributed to EBV infection. Extra-immune manifestations, including hepatic and neurological abnormalities, have recently been reported. EBV-associated lymphomas remain the main cause of severe morbidity. Unfortunately, treatment options to address the underlying mechanism of disease remain limited and Mg2+ supplementation has not proven successful. Here, we review the expanding clinical phenotype and recent advances in glycobiology that have increased our understanding of XMEN disease. We also propose updating XMEN to "X-linked MAGT1 deficiency with increased susceptibility to EBV-infection and N-linked glycosylation defect" in light of these novel findings.

Plasma magnesium is inversely associated with Epstein-Barr virus load in peripheral blood and Burkitt lymphoma in Uganda.

BACKGROUND: Epstein-Barr virus (EBV) causes endemic Burkitt lymphoma (eBL). EBV control was improved by magnesium (Mg2+) supplementation in XMEN, an X-linked genetic disease associated with Mg2+ deficiency, high circulating EBV levels (viral loads), and EBV-related lymphomas. We, therefore, investigated the relationship between Mg2+ levels and EBV levels and eBL in Uganda. METHODS: Plasma Mg2+ was measured in 45 women with low or high circulating EBV levels, 40 pediatric eBL cases, and 79 healthy children. Mg2+ uptake by T-lymphocytes was evaluated in samples from healthy donors. RESULTS: Plasma Mg2+ deficiency (plasma level <1.8 mg/dl) was more likely in women with high- vs. low-EBV levels (76.0% vs. 35%; odds ratio [OR] 11.3, 95% CI 2.14-60.2), controlling for age, and in eBL cases than controls (42.0% vs. 13.9%; OR 3.61, 95% CI 1.32-9.88), controlling for sex, age group, and malaria status. Mg2+ uptake by T-lymphocytes was related to extracellular Mg2+ concentration. INTERPRETATION: Plasma Mg2+ deficiency is associated with high EBV levels and eBL.

Mg2+ regulates cytotoxic functions of NK and CD8 T cells in chronic EBV infection through NKG2D.

The magnesium transporter 1 (MAGT1) is a critical regulator of basal intracellular free magnesium (Mg(2+)) concentrations. Individuals with genetic deficiencies in MAGT1 have high levels of Epstein-Barr virus (EBV) and a predisposition to lymphoma. We show that decreased intracellular free Mg(2+) causes defective expression of the natural killer activating receptor NKG2D in natural killer (NK) and CD8(+) T cells and impairs cytolytic responses against EBV. Notably, magnesium supplementation in MAGT1-deficient patients restores intracellular free Mg(2+) and NKG2D while concurrently reducing EBV-infected cells in vivo, demonstrating a link between NKG2D cytolytic activity and EBV antiviral immunity in humans. Moreover, these findings reveal a specific molecular function of free basal intracellular Mg(2+) in eukaryotic cells.