Dementia Alzheimer's Type

This is a randomized, placebo-controlled Phase 2 study to evaluate the efficacy and safety of SAR448851 in early Alzheimer's disease (AD) participants. The purpose of this study is to measure efficacy and safety with once daily oral SAR448851 compared to placebo in participants with mild cognitive impairment due to AD or mild AD dementia and with evidence of cerebral amyloid pathology. This Phase 2 study has 2 parts: Part A is a randomized, double-blind, parallel-group, placebo-controlled study with SAR448851 oral once daily. Part B is an open-label extension. All participants who complete Part A may continue to Part B. An optional dose 2 cohort will be considered to evaluate the efficacy and safety of SAR448851 dose 2 oral once daily. The study duration will be up to 111 weeks for Part A and B, and up to 63 weeks for the dose 2 cohort. The treatment duration will be up to 96 weeks for Part A and B, and up to 48 weeks for the dose 2 cohort. Up to 160 participants will be included in this study.