| Summary: | Summary: We identified osteoclast defects in craniometaphyseal dysplasia (CMD) using an easy-to-use protocol for differentiating osteoclasts from human induced pluripotent stem cells (hiPSCs). CMD is a rare genetic bone disorder, characterized by life-long progressive thickening of craniofacial bones and abnormal shape of long bones. hiPSCs from CMD patients with an in-frame deletion of Phe377 or Ser375 in ANKH are more refractory to in vitro osteoclast differentiation than control hiPSCs. To exclude differentiation effects due to genetic variability, we generated isogenic hiPSCs, which have identical genetic background except for the ANKH mutation. Isogenic hiPSCs with ANKH mutations formed fewer osteoclasts, resorbed less bone, expressed lower levels of osteoclast marker genes, and showed decreased protein levels of ANKH and vacuolar proton pump v-ATP6v0d2. This proof-of-concept study demonstrates that efficient and reproducible differentiation of isogenic hiPSCs into osteoclasts is possible and a promising tool for investigating mechanisms of CMD or other osteoclast-related disorders. : In this article, Chen and colleagues generated isogenic hiPSCs with or without ANKH mutations identified in patients with craniometaphyseal dysplasia (CMD). By differentiating hiPSC into osteoclasts, they demonstrate that mutations in ANKH lead to decreased osteoclast formation, marker gene expression, and bone resorption. Furthermore, hiPSC osteoclasts from CMD patients have decreased protein levels of ANKH and the vacuolar proton pump ATP6v0d2. Keywords: hiPSC differentiated osteoclasts, craniometaphyseal dysplasia, rare genetic bone disorder, osteoclastogenesis
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