ESPE Abstracts

The use of recombinant adeno-associated viruses (rAAV) as safe vectors have allowed hundreds of gene therapy attempts to treat monogenic diseases not including bone genetic diseases (Gao G, Nat Rev Drug Dis 2019). To our knowledge, there has been few attempts to apply gene therapy to monogenic bone diseases, largely because most skeletal malformations are being developed during fetal life. Patients affected with acrodysostosis are known to aggravate their skeletal malformations during postnatal development and to suffer from various organ dysfunctions related to the impairment of the PKA pathway.

We have produced an acrodysostotic mouse model as a knock-in (KI) of the recurrent R368X mutation to characterize phenotypic traits and attempt their correction with gene therapy. Heterozygous mice recapitulate the major phenotypic traits of the human disease, notably the skeletal and renal abnormalities (Le Stunff, J Bone Min Res 2017). Herein we report our preliminary observations of the use of rAAV in this model. We designed a therapeutic cassette made of the CAG promoter and the human PRKAR1A cDNA (single strand). We validated the function of this cassette by plasmid transfection in HEK cells, then produced a AAV9 vector carrying this cassette. At 1 month of age, KI R368 mice were injected intravenously with 2 x 10¹³ vg/kg (n=9) or PBS (n=8). Littermate WT mice (n=11) were sham injected as controls. Mice were kept alive to follow phenotypic traits, thus we do not have yet data about biodistribution and expression of the vector in body tissues.

Our preliminary results show that after 6 months of follow-up, the growth of the vector-injected mice was 15-20% more rapid than the PBS-injected mice and was 85% of the wild type control mice. Urinary cAMP measurements at 4 months showed a non-significant diminution in the treated mice. Despite the observed effect in skeletal growth and renal physiology, the small number of mice in each group did not allow statistics to be significant. Further studies are needed to confirm our observation in a larger group of diseased mice followed 1 yr and to study the skeletal and renal expression of the vector.

Although yet preliminary, the current data are encouraging for attempting gene therapy in various genetic bone diseases if it may improve patients' clinical status.