The observations that wt IDH1 has a lower KM for Mg2+ than R132H IDH1 (Table 1) and that the potency of the R132H inhibitors increases as the Mg2+ concentration decreases (Fig. 6) raise the possibility of a therapy for R132H IDH1 bearing cancers in which inhibitor treatment is combined with restriction of Mg2+ (possibly by diet therapy or inhibitors blocking Mg2+ uptake). The gene discussed is IDH1; the disease is cancer.