Tmprss6^–/– mice, regardless of their Fgf23 genotype, show EPO elevation and increased circulating levels of cFGF23. (A) Serum EPO, (B) plasma cFGF23, and (C) plasma iFGF23 of 8-week-old male mice with different Tmprss6-Fgf23 genotype combinations (n = 5-7 per group). Using two-way ANOVA in male mice, Tmprss6 genotype had statistically significant effects on serum EPO (P < .0001), plasma cFGF23 (P < .0001), and plasma iFGF23 (P = .0081), whereas the Fgf23 genotype had no significant effect on these parameters. (D) Serum EPO, (E) plasma cFGF23, and (F) plasma iFGF23 of 8-week-old female mice with different Tmprss6-Fgf23 genotype combinations (n = 5-8 per group). Two-way ANOVA in female mice revealed statistically significant effects of both Tmprss6 and Fgf23 genotypes on serum EPO (Tmprss6 genotype: P < .0001; Fgf23 genotype: P = .0297), plasma cFGF23 (Tmprss6 genotype: P < .0001; Fgf23 genotype: P = .0075), and plasma iFGF23 (Tmprss6 genotype: P = .0191; Fgf23 genotype: P = .0063). For panels A-F, data represent mean ± standard deviation. ∗P < .05; ∗∗P < .01; ∗∗∗P < .001; and ∗∗∗∗P < .0001 using two-way ANOVA with Tukey post hoc test. (G) Plasma cFGF23 vs serum EPO and (H) plasma iFGF23 vs serum EPO in individual Fgf23^+/+ mice with different Tmprss6 genotypes (8-week-old mice, both sexes pooled): ^+/+ male (●), ^+/− male (▲), ^–/– male (■), ^+/+ female (○), ^+/− female (△), and ^–/– female (□). R² represents the coefficient of determination using a linear regression model (ie, goodness of fit). The P value of the Pearson correlation is shown.