Saliva levels of Abeta1-42 as potential biomarker of Alzheimer's disease: a pilot study

Background: Simple, non-invasive tests for early detection of degenerative dementia by use of biomarkers are urgently required. However, up to the present, no validated extracerebral diagnostic markers for the early diagnosis of Alzheimer disease (AD) are available. The clinical diagnosis of probable AD is made with around 90% accuracy using modern clinical, neuropsychological and imaging methods. A biochemical marker that would support the clinical diagnosis and distinguish AD from other causes of dementia would therefore be of great value as a screening test. A total of 126 samples were obtained from subjects with AD, and age-sex-matched controls. Additionally, 51 Parkinson's disease (PD) patients were used as an example of another neurodegenerative disorder. We analyzed saliva and plasma levels of beta amyloid (A beta) using a highly sensitive ELISA kit. Results: We found a small but statistically significant increase in saliva A beta(42) levels in mild AD patients. In addition, there were not differences in saliva concentration of A beta(42) between patients with PD and healthy controls. Saliva A beta(40) expression was unchanged within all the studied sample. The association between saliva A beta(42) levels and AD was independent of established risk factors, including age or Apo E, but was dependent on sex and functional capacity. Conclusions: We suggest that saliva A beta(42) levels could be considered a potential peripheral marker of AD and help discrimination from other types of neurodegenerative disorders. We propose a new and promising biomarker for early AD.