Genetic polymorphism in β-site amyloid precursor protein-cleaving enzyme 1 affects the structure of medial temporal lobe and cognition in Alzheimer's disease: an exploratory study

The β-site amyloid precursor protein-cleaving enzyme 1 (BACE1) gene polymorphism (rs638405) has been widely reported to be associated with Alzheimer's disease (AD) risk. However, studies on the relationship between BACE1 gene polymorphism (rs638405), brain volume, and cognition in AD patients remain scarce. To investigate the effect of genetic polymorphism in BACE1 on gray matter volume (GMV) and cognition in AD, this study recruited 111 cognitively unimpaired (CU) controls and 144 AD patients. The effect of BACE1 rs638405 polymorphism on cognition was explored in CU and AD groups. Then the interaction effect of the diagnosis and BACE1 rs638405 polymorphism on GMV was performed, following the post-hoc analysis of regions of interest (ROIs) in interaction analysis. Mediation analysis was used to elucidate the relationship among genotypes, ROIs and cognition. BACE1 rs638405 G carriers (BACE1 G+) showed significantly lower scores in global cognition and memory function than noncarriers (BACE1 G-) in AD group. Genotypes (G+/G-) and diagnosis (CU/AD) have interaction on GMV of medial temporal lobe (MTL) including the left parahippocampus and right hippocampus. Post-hoc analysis revealed that BACE1 G+ exhibited significantly lower GMV in ROIs compared to BACE1 G- in AD. Finally, mediation analysis further demonstrated that the GMV of ROIs mediated the effect of BACE1 rs638405 polymorphism on cognition in AD. Our results emphasize the BACE1 rs638405 gene polymorphisms may affect the GMV of MTL and cognition in AD, deepening the understanding of AD pathogenesis.