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

Inclusion: For the treatment group * 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. * Parent/legal guardian willing to provide written informed consent for their child prior to participation in the study, * Subjects and caregivers must demonstrate the ability to travel to the study center. For the 30 days post treatment subjects must reside within 100 miles (approximately 160 km) of the clinical site. For the control group * Male and females between the ages of 4 to 72 months at the time of screening. * A molecularly confirmed diagnosis of SPG47, SPG50 or SPG52 (confirmed by a CLIA certified, CE-marked, or equivalent lab). Genomic DNA mutation analysis demonstrating bi-allelic pathogenic variants in the AP4B1, AP4M1, or AP4S1 gene, * Subjects must have features of n…