Prediction of Alzheimer’s Disease Using the CSF Aβ42/Aβ40 Ratio in Patients with Mild Cognitive Impairment

Evidence supports an important role for beta-amyloid (Abeta) in the pathogenesis of Alzheimer's disease (AD). Here, we investigate baseline levels of the 40- and 42-amino-acid-long Abeta peptides (Abeta40 and Abeta42) in cerebrospinal fluid (CSF) from a cohort of patients with mild cognitive impairment (MCI, n = 137) in relation to the final diagnosis after 4-6 years of follow-up time. CSF Abeta42 concentration at baseline and the Abeta42/Abeta40 ratio were significantly decreased in the MCI patients who developed AD as compared to cognitively stable MCI patients and MCI patients who developed other forms of dementia (p < 0.001). The baseline levels of Abeta40 were similar in all MCI groups but correlated with change in Mini Mental State Examination scores in converters to AD. The Abeta42/Abeta40 ratio was superior to Abeta42 concentration with regard to identifying incipient AD in MCI (p < 0.05). In conclusion, the data provide further support for the view that amyloid precursor protein metabolism is disturbed in early sporadic AD and points to the usefulness of the Abeta42/Abeta40 ratio as a predictive biomarker for AD.