XMEN: welcome to the glycosphere.

XMEN (X-linked immunodeficiency with magnesium defect, EBV infection, and neoplasia) is a complex primary immunological deficiency caused by mutations in MAGT1, a putative magnesium transporter. In this issue of the JCI, Ravell et al. greatly expand the clinical picture. The authors investigated patients' mutations and symptoms and reported distinguishing immunophenotypes. They also showed that MAGT1 is required for N-glycosylation of key T cell and NK cell receptors that can account for some of the clinical features. Notably, transfection of the affected lymphocytes with MAGT1 mRNA restored both N-glycosylation and receptor function. Now we can add XMEN to the ever-growing family of congenital disorders of glycosylation (CDG).