Impaired bone formation rate in KRN/G7 mice. (A) Osteoblast number/millimeter bone perimeter (No. OB/B.mm). (B) Percentage trabecular surface covered by osteoid (OS.S/B.mm). (C) Bone formation rate (BFR) histomorphometrically quantitated from double calcein labeled tibia. (D) In vivo bone formation was quantified by serum osteocalcin (Osc) level at 6 weeks of age (n = 5). (E) RNA of KRN and KRNxG7 BM was analyzed for gene expression of osteoblast markers, receptor activator of nuclear factor-κB ligand (Rankl), Osteoprotegerin (Opg), Runx2, and Osteocalcin by quantitative RT-PCR. Shown is the mean expression ± SD for each gene normalized to GAPDH. *P < .05. **P < .01. ***P < .001.