Eight subjects were enrolled into two dose cohorts of the trial.
The international trial is being carried out at sites in the US and Brazil.
Further interim findings from the trial are anticipated to be reported in the first half of next year.
Assessing the safety of RGX-111 is the primary endpoint of the trial.
Biomarkers of IDUA enzyme activity in the cerebrospinal fluid (CSF), serum, and urine, as well as neurodevelopmental evaluations and caregiver-reported outcomes, comprise the secondary and exploratory endpoints.
A one-time gene therapy, RGX-111 offers the gene that encodes the α-l-iduronidase (IDUA) enzyme leveraging the NAV AAV9 vector.
RegenxBio chief medical officer Steve Pakola said: “We have made great progress this year advancing our pipeline of neurodegenerative disease programmes, and completing the dosing in this MPS I trial is another important clinical milestone as we continue to develop potential one-time gene therapies for patients.
“We intend to advance the programme for RGX-111, with the aim of providing a much-needed new treatment option for the MPS I community as quickly as possible.”
The company intends to continue having initial and frequent discussions with regulatory authorities about pathways to speed up the neurodegenerative disease pipeline development.
In the first half of next year, the company plans to utilise its Manufacturing Innovation Center for producing RGX-111 commercial-scale cGMP material from its NAVXPress suspension-based manufacturing process.
A rare autosomal recessive genetic ailment, MPS I is caused by a lysosomal enzyme IDUA deficiency.