Lysogene reports biomarker data from the ongoing AAVance clinical trial with LYS-SAF302 for the treatment of MPS IIIA (NCT03612869) presented at the WORLDSymposium™ 2021 by Dr. Michaël Hocquemiller, Head of Non-Clinical Development, during the Late-Breaking Science session held on February 12, 2021. Concentration of heparan sulfate (HS) in the cerebrospinal fluid (CSF) has been analyzed in 9 patients so far, with samples at baseline (n=9), 6 months (n=8) and 12 months (n=5) after LYS-SAF302 administration. The concentration of abnormally elevated HS-derived oligosaccharides in the CSF was reduced from baseline by 27% and 30% at 6 and 12 months, respectively (p<0.005 and p<0.05 by paired t-test vs baseline, respectively). In contrast, changes in HS concentrations in serum samples from the same patients were not statistically significant, confirming that the reduction of HS in CSF after LYS-SAF302 treatment is linked to a reduction of HS entering the CSF from the brain parenchyma and not an indirect consequence of a reduction of HS entering the CSF from extra-parenchymal sources, such as choroid plexus or blood. Additionally, changes in dermatan sulfate (DS) and keratan sulfate (KS), which do not accumulate in MPS IIIA, were not statistically significant in serum and CSF, confirming the specificity of HS accumulation in the CSF.