CD4 and Tangier disease: These findings suggest that hypomagnesemia may serve as an early prognostic biomarker for delayed immune reconstitution, reduced CD4+ T cell counts, and prolonged engraftment in pediatric allo-HSCT recipients, and, with significant clinical implications, provide novel evidence of a potential interplay between magnesium deficiency, iron overload, and impaired immune recovery post-transplant [13].