The amyloid-β oligomer count in cerebrospinal fluid is a biomarker for Alzheimer's disease.

Recent studies indicate that small amyloid- peptide (A) oligomers are the major toxic species responsible for development and progression of Alzheimer's disease (AD). Therefore, we suggest that the number of A oligomers in body fluids is the most direct and relevant biomarker for AD. Determination of the A oligomer content of cerebrospinal fluid (CSF) samples from 14 AD patients and 12 age-matched controls revealed a clear distinction between both groups. All samples of the control group showed homogenously low numbers of A oligomers, while the samples of the AD group exhibited significantly higher levels of A oligomers. The A oligomer numbers correlated with the patients' Mini-Mental State Examination scores. This indicates that the quantity of A oligomers in CSF reflects the severity of the disease and that A oligomers play a crucial role in AD pathology and in turn can be used as a diagnostic biomarker.