BACE1 and Alzheimer disease: As this association was present in persons with AD dementia but not in individuals with NCI or MCI, who present with lesser β-amyloid load, and since bace-1 methylation levels are similar across NCI, MCI and AD groups, this suggests that in the human brain very large amounts of Aβ peptides in the form of plaques are needed to impact methylation in the dorsolateral prefrontal cortex.