Magnesium (Mg2+) is an abundant cation that is important for many intracellular biochemical functions, especially as a cofactor for ATP. Intracellular Mg2+ concentrations must be finely regulated and recently, transporters for this cation have been elucidated. The human genes SLC41A1 and SLC41A2 encode magnesium transport proteins 1 and 2 respectively (MagT1 and MagT2). They both mediate the uptake of Mg2+ into cells (Goytain A and Quamme GA, 2005; Sahni J et al, 2007). A third human gene, SLC41A3, is also thought to encode a MagT protein but has not been characterized yet.