Phase 3 Efficacy Study With Concurrent Control of IT MELPIDA in SPG50.Concurrent Controls.

Male and females between the ages of 4 months to 72 months at the time of screening.

Molecularly-confirmed diagnosis of SPG50 (confirmed by a CLIA certified, CE-marked, or equivalent lab): Genomic DNA mutation analysis demonstrating bi-allelic pathogenic or likely pathogenic variants in the AP4M1 gene.

Subjects must have features of neurologic dysfunction by clinical history and physical examination.

Stable doses of concomitant medications such as anti-spasticity medications, anti-seizure medications, behavioral management medications, sleep medications, and special diets, supplements, or nutritional support for at least 3 months prior to Screening. If recent changes (< 3 months) in medications, the subject may be allowed per Investigator judgement.