Establishment of FGF23-null mice. (a) Targeted ablation of Fgf23 gene. Construct of a targeting vector (top), wild-type allele (middle), and targeted mutant allele (bottom) are shown. DT-A, diphtheria toxin-A fragment; H, HindIII. (b) Genomic Southern blot analysis. Genomic DNAs (5 μg) isolated from transfected ES clones were digested with HindIII and hybridized to the indicated probe. (c) Gross phenotypes of heterozygous and homozygous founders at 6 weeks of age. (d) Growth curves and (e) survival ratios for male (filled) or female (open) WT (circles), heterozygotes (triangles), and homozygotes (squares). Data are represented as mean ± SEM. Statistical analysis in each sex was carried out by Dunnett’s method. Statistically significant results are marked by asterisk (male) or cross (female) (*P < 0.05, §P < 0.01, †P < 0.05, #P < 0.01). Numbers of animals used in this study: male WT (+/+), n = 9; female WT, n = 15; male heterozygotes (+/–), n = 20; female heterozygotes, n = 19; male homozygotes (–/–), n = 7; female homozygotes, n = 6.