Phase 2/3 study of gene therapy for young children with MPS IIIA yields mixed results

Lysogene has announced topline results from its phase 2/3 study evaluating LYS-SAF302, an investigational gene therapy for the treatment of mucopolysaccharidosis type IIIA, or Sanfilippo syndrome.

According to a company release, six patients aged younger than 30 months who were enrolled in the open-label, single-arm multicenter AAVance study had statistically significant improvement in cognitive development, as assessed by Bayley Scales of Infant and Toddler Development (third edition), compared with natural history at 24 months post-dosing.

This cohort also achieved secondary efficacy criteria, including percent of participants with stabilized or improved cognitive, language or motor developmental age at 24 months relative to baseline, and evolution of Vineland Adaptive Behavior Scales (second edition) scores compared with natural history data.

However, the company stated that the study did not meet its primary efficacy outcome in the main cohort of 12 patients aged 30 months and older at enrollment compared with the natural history cohort. In addition, key secondary efficacy endpoints were not met.

“While we are disappointed with the results in the main cohort of the patients enrolled at 30 months or older, these can likely be explained by the rapid progression of the disease and the recent learning from other clinical studies that gene therapy treatment of neurodegenerative diseases should be initiated at the earliest possible age in order to provide a therapeutic benefit before the onset of irreversible neuronal damage,” Karen Aiach, founder, chairman and CEO of Lysogene, said in the release.

According to the release, the safety and tolerability of LYS-SAF302 was consistent with what has been previously communicated, namely that white matter abnormalities were observed on the MRIs near injection sites in all treated patients.

In addition, lesions have stabilized or diminished in size in most patients and no clinically significant symptoms have been observed that can be directly attributed to white matter abnormalities. Other adverse effects observed were consistent with the natural history of disease.

Lysogene also stated in the release that it will complete full analysis and evaluation of data from the main study cohort and work with investigators on future presentation and publication of the results.

“I look forward to continuing to work with Lysogene to analyze the phase 2/3 data and determine the most appropriate path to bringing gene therapy with LYS-SAF302 to those patients who have the highest potential to benefit from it,” Chester B. Whitley, MD, PhD, principal investigator of Lysosomal Disease Network and professor of pediatrics and experimental and clinical pharmacology at the University of Minnesota, said in the release.