Alzheimer’s Diseases: Towards Biomarkers for an Early Diagnosis

Abstract

Alzheimer’s diseases (AD) are the most frequent dementias across the world and represent more than 60% of all neurodegenerative dementias including those with Lewy bodies (DLB) and frontotemporal lobar degeneration (FTLD). Most neurodegenerative dementias are induced by aggregation of different brain proteins; they are nosologically grouped into a large pathological entity named proteinopathy. Prevalence of dementias is more than 20% in 85 years old aged population and linearly increases with the age (Ferri, Prince et al. 2005). The international impact of degenerative dementias across the world is estimated to touch more than 24 million patients with an incidence about 4.6 million new cases by year. Diagnosis of AD is still based on the integration of clinical examination, neuropsychological data, radiological and biological analyses. The final diagnosis is established after neuropathological examination of brain and observation of typical cerebral failures, in consequence, the clinical diagnosis is “probable AD” when typical criteria are found and “possible AD” if atypical elements are present during clinical examination. Nevertheless, the clinical diagnosis performance for “probable AD” is relatively low with a sensitivity and a specificity of 80% and 70% respectively (Knopman, DeKosky et al. 2001). Because a consequent clinical overlap does exist between etiological AD and others causes of dementia, the clinical diagnosis specificity for a possible AD is less than 50%. Paraclinical analyses such as radiological and biological examinations tend to increase accuracy of differential diagnoses as well as diagnosis precocity for these patients.