Treatment with Minicircle DNA Expressing a FGF23 Fragment in a Clinically relevant Mouse Model of X-Linked...

X-linked hypophosphatemic rickets (XLHR) is a rare X-linked dominant skeletal dysplasia caused by phosphate regulating endopeptidase homolog X-linked (PHEX) gene mutation. Until now, the pathogenic role of PHEX has not been fully determined, and there has been no radical cure for XLHR. In the previous study, a novel PHEX variant (c.T1349C; p.L450P) is identified in a child with XLHR. The present study aims to reveal its pathogenic role and evaluate the therapeutic effects of the minicircle (MC)-DNA in XLHR. In vitro, the wildtype and mutant plasmids are introduced into HEK293 cells. In vivo, a new knock-in XLHR mouse model carrying the novel variant is established. Furthermore, this study makes the first attempt to perform gene therapy using a MC-DNA vector expressing a fragment of FGF23 (amino acids 180-251) in the Phex-T1349C mice. The new mouse model demonstrates the clinical manifestations of XLHR seen in the patient, including a gene dosage effect. Furthermore, MC-DNA is found to slightly increase blood phosphorus levels, significantly decrease serum alkaline phosphatase levels, and improve bone mineralization without apparent adverse effects for at least 6 weeks. This study suggests MC-DNA as a promisingly safe and effective therapeutic strategy to treat XLHR.