Cerebrospinal fluid amyloid β_1-42 levels in the mild cognitive impairment stage of Alzheimer's disease

Cerebrospinal fluid (CSF) levels of amyloid β-protein ending at amino acid position 42 (CSF-A β_1-42) and CSF-tau levels were quantified by sandwich ELISAs in 19 patients with mild cognitive impairment (MCI) who eventually developed Alzheimer's disease (AD) on follow-up as well as in 15 age-matched normal controls and 54 AD patients at diverse stages of the disease. In the present study, the annual conversion rate was approximately 15%. The CSF-A β_1-42 levels did not differ significantly between the normal control group and the MCI group, however, these values declined significantly once AD became clinically overt. In contrast to CSF-A β_1-42, CSF-tau levels were significantly increased in the MCI stage, and these values continued to be elevated thereafter, indicating that increased levels of CSF-tau may help in detecting MCI subjects who are predicted to develop AD. We propose that CSF-tau and CSF-A β_1-42 must be used as two distinct biomarkers that should be applied appropriately in clinical settings.