Biological Markers and Early Diagnosis of AD

With regard to AD, antemortem biochemical markers have been sought for years in different tissues and cells, such as CSF, plasma, erythrocytes [62], lymphocytes [63], urine [64, 65], hair [66, 67], and skin [68, 69]. 

In fact, despite the attempts to identify biochemical markers related to AD have led to promising results, the field is far from being satisfied, as the diagnostic value of most hitherto proposed biochemical markers has been limited by considerable overlap between AD patients, patients with other dementing illnesses, and normal subjects. 

One of the major difficulties in identifying potential biomarkers related to AD is likely a result of the fact that specific proteins involved in the pathogenetic mechanisms are low abundant in CSF and serum, while a small number of proteins such as albumin, transferrin, and immunoglobulins provide a significant background that makes it difficult to identify low-abundance proteins. 

More important, some biochemical markers were not at all designed to assess a given biochemical metabolite as a diagnostic test, as in some cases they were designed to study pathophysiological processes involved in neurodegeneration and to assess the possible involvement of the given metabolite in AD. 

Several studies have found that CSF levels of sAPPq are slightly decreased in AD compared to controls, with too much overlap for diagnostic utility, whereas levels of sAPP/3 do not appear to differ [70], 

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