Genetic variants beyond amyloid and tau associated with cognitive decline: A cohort study

To identify single nucleotide polymorphisms (SNPs) associated with cognitive decline independent of β-amyloid (Aβ) and tau pathology in Alzheimer disease (AD).

Discovery and replication datasets consisting of 414 individuals (94 cognitively normal control [CN], 185 with mild cognitive impairment [MCI], and 135 with AD) and 72 individuals (22 CN, 39 with MCI, and 11 with AD), respectively, were obtained from the Alzheimer's Disease Neuroimaging Initiative database. Genome-wide association analysis was conducted to identify SNPs associated with individual cognitive function (measured with the Mini-Mental State Examination and Alzheimer's Disease Assessment Scale-Cognitive Subscale ) while controlling for the level of Aβ and tau (measured as CSF phosphorylated-tau/Aβ_1-42). Gene ontology analysis was performed on SNP-associated genes.

We identified 1 significant (rs55906536, β = -1.91, standard error 0.34, p = 4.07 × 10^-8) and 4 suggestive variants on chromosome 6 that were associated with poorer cognitive function. Congruent results were found in the replication data. A structural equation model showed that the identified SNP deteriorated cognitive function partially through cortical thinning of the brain in a region-specific manner. Furthermore, a bioinformatics analysis showed that the identified SNPs were associated with genes related to glutathione metabolism.

In this study, we identified SNPs related to cognitive decline in a manner that could not be explained by Aβ and tau levels. Our findings provide insight into the complexity of AD pathogenesis and support the growing literature on the role of glutathione in AD.