An international team of researchers led by Tony Wyss-Coray of the Department of Neurology and Neurological Sciences at Stanford University School of Medicine report that they have developed a blood test that can predict with 90% accuracy the early stages of Alzheimer's Disease.

By analyzing the concentrations of 18 different biomarkers, Wyss-Coray and his colleagues were able to identify, long before any symptoms were evident, those patients with mild cognitive impairment that progressed to Alzheimer's 2-6 years later.

Alzheimer's Disease is a progressive neurodegenerative disorder which can take up to 20 years to develop. Its early diagnosis is extremely difficult, because patients do not present with the characteristic symptoms until later stages of the disease, by which time irreparable damage to the brain has already occurred.

This is complicated by the fact that not all patients who are diagnosed with mild cognitive impairment go on to develop Alzheimer's, and because there are many other possible causes of some of the symptoms of the condition. An unequivocal diagnosis of Alzheimer's therefore is only obtained upon post-mortem.

The researchers collected 259 blood plasma samples from individuals with different stages of the condition. Some of the samples were taken from healthy people, and others from patients with mild cognitive impairment and with late-stage Alzheimer's. All of the people from whom sampels were taken were followed up, to determine which of them developed Alzheimer's.

Sophisticated microarray technology was then used to compare the plasma concentrations of 120 well-known signalling proteins from these samples to those obtained from healthy individuals. Towards the end of the study, a statistical analysis showed differential expression of 18 of the proteins in those patients who later went on to develop Alzheimer's.

This "signature" of biomarkers included proteins that are involved in the immune response, brain inflammation, neuroprotection, haematopoesis (blood formation) and apoptosis (programmed cell death), all of which have recently been implicated in the complex aetiology of the condition.

The new findings suggest that a test for easily - and cheaply - diagnosing Alzheimer's early on may be available in the foreseeable future. The ability to diagnose the disease at its earliest stages will be essential in providing treatments that can effectively slow its progression.

Reference:

Ray, S., et al. (2007). Classification and prediction of clinical Alzheimer's diagnosis based on plasma signaling proteins. Nat. Med. DOI:10.1038/nm1653. [Abstract]