iPSC-based modeling reveals defects in chondrogenic and osteogenic differentiation in VKCFD1

Introduction Vitamin K (VK) is a crucial cofactor for hemostasis, enabling γ-carboxylation and subsequent activation of several pro- and anti- coagulant factors. Homo- or compound heterozygous mutations in γ-glutamyl carboxylase (GGCX), the enzyme catalyzing VK–dependent (VKD) γ-carboxylation, cause a bleeding tendency classified as VKD coagulation factor deficiency type 1 (VKCFD1). Importantly, VKCFD1 manifests beyond coagulation defects; patients may experience diverse abnormalities, including skeletal deformities such as mid-facial hypoplasia, strippling of fingers and growth delay. These most likely reflect defective γ-carboxylation of other VKD proteins (VKDPs) involved in bone and cartilage metabolism [ 1 ]. Key VKDPs in this respect include osteocalcin, which regulates bone mineralization, and MGP, which prevents ectopic calcification [ 2 ]. However, the underlying mechanism is unknown. Notably, VK 1 supplementation is a common treatment to restore hemostasis while an effective therapy to treat non-hemostatic phenotypes in VKCFD1 patients is still unclear [ 3 ]. This discrepancy highlights the need to investigate how GGCX mutations and VK metabolism influence the development and maintenance of bone and cartilage. Method Induced pluripotent stem cells (iPSCs) derived from VKCFD1 patients with and without skeletal abnormalities and healthy controls were differentiated into mesenchymal stem cells (MSCs). MSCs were subsequently directed towards osteo- or chondrogenic lineages using established protocols and further analyzed for their potential to differentiate properly. Chondrocytes were analyzed for glycosaminoglycan content in 3D pellet cultures. Early osteogenic differentiation was assessed by alkaline phosphatase (ALP) staining and fluorometric ALP activity. Matrix mineralization was evaluated by calcium deposition, optical density, and phosphate ion release. Expression of lineage-specific markers was quantified. Results Patient-derived MSCs showed impaired osteogenic differentiation and decreased matrix mineralization. Chondrogenic differentiation was also affected, as indicated by lower glycosaminoglycan content. The severity of these defects depended on the specific mutation and phenotype. Conclusion Differentiation of iPSCs into osteo- and chondrogenic lineages has the potential to uncover precise pathophysiological pathways and identify targeted therapeutic strategies in a patient-specific setting. Thus, employing iPSC models to dissect the impact of VK deficiency and GGCX mutations on bone and cartilage development promises insights essential for improving clinical management beyond coagulation correction. Future studies in the patient-specific iPSC model will address whether distinct VK forms, particularly VK 2 , can enhance γ-carboxylation of relevant extra-hepatic VKDPs and thereby restore bone and cartilage differentiation in GGCX-deficient cells. In the long term, this approach may pave the way for targeted therapies to mitigate or prevent skeletal malformations in VKCFD1 patients. Publication History Article published online: 17 February 2026 © 2026. Thieme. All rights reserved. Georg Thieme Verlag KG Oswald-Hesse-Straße 50, 70469 Stuttgart, Germany