ALZHEIMER'S DISEASE BIOMARKERS AND COGNITION

Lowered cerebrospinal fluid (CSF) levels of Aβ 1-42, and heightened levels of t-tau, p-tau levels are found in Alzheimer's disease (AD). They are reliable biomarkers in diagnosis of AD, but their value in predicting disease severity is controversial. In this study, we asked whether levels of these biomarkers are associated with cognitive function in AD and in Parkinson's disease (PD), another neurodegenerative disease with different protein pathology. We studied 16 patients with mild to moderate AD, 9 patients with PD, and 14 cognitively normal controls. Neuropsychological evaluation was performed in all subjects. CSF was collected and stored in a standardized protocol. We determined CSF Aβ 1-42, t-tau, p-tau levels using ELISA (Innotest, Innogenetics, Ghent, Belgium). MMSE scores of AD, PD patients and controls were 17.6±6.8, 24.7±6.6 and 27.1±3.5, respectively. CSF Aβ 1-42 level was lower in AD than in PD and controls (814.5±335.8 vs 1165.8±185.8 and 1207.2±197.9; p<0,05). In AD, both CSF t-tau (629.5±237.5 vs 212.5±139.8 and 258.5±163.4) and p-tau levels (89.9±28.4 vs 43.7±19.8 and 42.2±22.9) were significantly higher than in PD and the controls. CSF levels of none of these proteins correlated with any of the cognitive test scores including MMSE in AD or PD groups. But t-tau and p-tau levels are positively correlated with age and negatively correlated with MMSE in the whole study groups (p<0.05). CSF levels of biomarkers related to neuronal pathology such as t-tau was highly correlated with cognitive functions in previous studies involving large subject groups. On the other hand, CSF levels of markers for amyloid deposition such as Aβ 1-42 were not significantly related to clinical symptoms and cognitive severity in those studies. Here, we did not find any association of CSF levels of Aβ 1-42, t-tau and p-tau and measures of cognitive functions in AD and also in PD. Further studies in larger study groups are necessary to show differential association of AD biomarkers in cognitive functions of AD and PD. Funded by TUBITAK (SBAG 112S360).