Gain-of-function mutation in TRPV4 identified in patients with osteonecrosis of the femoral head

Background Osteonecrosis of the femoral head is a debilitating disease that involves impaired blood supply to the femoral head and leads to femoral head collapse. Methods We use whole-exome sequencing and Sanger sequencing to analyse a family with inherited osteonecrosis of the femoral head and fluorescent Ca²⁺ imaging to functionally characterise the variant protein. Results We report a family with four siblings affected with inherited osteonecrosis of the femoral head and the identification of a c.2480_2483delCCCG frameshift deletion followed by a c.2486T>A substitution in one allele of the transient receptor potential vanilloid 4 (TRPV4) gene. TRPV4 encodes a Ca²⁺-permeable cation channel known to play a role in vasoregulation and osteoclast differentiation. While pathogenic TRPV4 mutations affect the skeletal or nervous systems, association with osteonecrosis of the femoral head is novel. Functional measurements of Ca²⁺ influx through mutant TRPV4 channels in HEK293 cells and patientderived dermal fibroblasts identified a TRPV4 gain of function. Analysis of channel open times, determined indirectly from measurement of TRPV4 activity within a cluster of TRPV4 channels, revealed that the TRPV4 gain of function was caused by longer channel openings. Conclusions These findings identify a novel TRPV4 mutation implicating TRPV4 and altered calcium homeostasis in the pathogenesis of osteonecrosis while reinforcing the importance of TRPV4 in bone diseases and vascular endothelium.