The role of bilingualism on functional decline and neurodegeneration in distinct ADRD clinical syndromes.

INTRODUCTION

We evaluated a large cohort (N = 408) of monolingual and bilingual speakers with Alzheimer's disease and related dementias (ADRD) syndromes and longitudinal markers of functional decline and neurodegeneration to determine whether bilingual speakers show more cognitive resilience to neurodegenerative processes.

METHODS

Participants (338 monolingual, 70 bilingual) were diagnosed based on established criteria and then categorized into five clinical groups (healthy controls and memory, language, behavioral, motor-predominant syndromes from participants living with ADRD). Linear mixed-effects models estimated longitudinal functional decline (Clinical Dementia Rating) and fluid ADRD biomarker trajectories (plasma neurofilament light chain (NfL) and plasma phosphorylated tau-217 (p-tau217).

RESULTS

Bilingual speakers showed slower progression of functional impairment and lower baseline NfL and p-tau217, but not slower biomarker trajectories, compared to monolingual speakers.

DISCUSSION: We found a protective effect of bilingualism on baseline levels of neuropathology and neurodegeneration and longitudinal functional decline, supporting a role of bilingualism in cognitive resilience across ADRDs.

HIGHLIGHTS: Explored longitudinal effects of bilingualism on functional decline, neurofilament light chain (NfL), andphosphorylated tau-217 (p-tau217). Used syndrome-defined cohorts of monolingual and bilingual speakers. First study using NfL and p-tau217 to study bilingualism's effects in cognitive resilience. Bilinguals showed slower progression of functional impairment. Bilinguals had lower baseline NfL and p-tau217 but longitudinal trajectories did not differ.