Fgfr3 gain-of-function mutation impacts bone homeostasis in hypochondroplasia mouse model

Correction of a knock-in mouse model of acrodysostosis with gene therapy using a rAAV9-CAG-human PRKAR1A vector

Acrodysostosis is a rare skeletal dysplasia caused by loss-of-function mutations in the regulatory subunit of protein kinase A (PRKAR1A). In a knock-in mouse model (PRKAR1A^wt/mut) expressing one copy of the recurrent R368X mutation, we tested the effects of a rAAV9-CAG-human PRKR1A (hPRKAR1A) vector intravenously administered at 4 weeks of age. Caudal vertebrae and tibial diaphyses contained 0.52 ± 0.7 and 0.13 ± 0.3 vector genome per cell (VGC), respectively, at 10 weeks of age and 0.22 ± 0.04 and 0.020 ± 0.04 at 16 weeks while renal cortex contained 0.57 ± 0.14 and 0.26 ± 0.05 VGC. Vector-mediated hPRKAR1A expression was found in growth plate chondrocytes, osteoclasts, osteoblasts, and kidney tubular cells. Chondrocyte architecture was restored in the growth plates. Body length, tail length, and body weight were improved in vector treated PRKAR1A^wt/mut mice, not the bone length of their limbs. These results provide one of the few proofs for gene therapy efficacy in a mouse model of chondrodysplasia. In addition, the increased urinary cAMP of PRKAR1A^wt/mut mice was corrected almost to normal. In conclusion, gene therapy with hPRKAR1A improved skeletal growth and kidney dysfunction, the hallmarks of acrodysostosis in R368X mutated mice and humans.