Single & Multiple Ascending Dose Study of SAR443820 in Healthy Adult Participants

This is a Phase 1, single-center study conducted in 2 parts: Part 1a, single ascending dose (SAD-TDU16519): Double-blind, randomized, placebo-controlled sequential ascending single oral doses including up to 6 cohorts. Each cohort will include 8 participants (6 receiving SAR443820 and 2 placebo). Part 1b (TDU16519): - Open label, single SAR443820 dose in one or two separated cohort(s) for SAR443820 measurements in CSF and in plasma. Part 2, multiple ascending dose (MAD -TDR16520): Double-blind, randomized, placebo-controlled, sequential ascending repeated oral doses for 14 days, including up to 4 cohorts. Each cohort will include 10 participants (8 receiving SAR443820 and 2 placebo).