Phase I/II/III Gene Transfer Clinical Trial of scAAV9.U1a.hSGSH

This gene therapy trial treats children with MPS IIIA (Sanfilippo Syndrome Type A) — a severe inherited disorder where a missing enzyme causes a buildup of sugar molecules in the brain, leading to progressive mental decline and early death. A single dose of a specially engineered gene therapy (scAAV9.U1a.hSGSH) is given to supply the missing gene and slow or stop the disease. You may be eligible if: - Your child has a confirmed diagnosis of MPS IIIA (through genetic testing and enzyme activity tests) - Your child is old enough and cognitively developed enough to meet the age requirements for each study cohort - Your child is at least 6 months old before receiving treatment - Vaccinations are up to date (for Cohort 4) You may NOT be eligible if: - Your child has two nonsense/null variants in the SGSH gene (for earlier cohorts) - Your child has an S298P mutation in the SGSH gene - Your child shows an attenuated (mild) form of the disease - Your child has a concomitant illness or chronic drug treatment that poses risks for gene transfer - Your child has had a previous bone marrow transplant or gene therapy - Antibody levels to the AAV9 virus are too high (for earlier cohorts) - Your child has active infections including HIV or hepatitis B or C - Your child has uncontrolled seizures or a severe heart condition Talk to your doctor to see if this trial is right for you.