Alzheimer's disease: the size of the problem, clinical manifestation and heterogeneity

Age is the major demographic risk factor for the development of Alzheimer's disease (AD) and the ageing of our society has contributed to the growing importance of AD. The problem of AD has been tackled from numerous clinical and scientific angles. The traditional clinico-pathological disease concept, which relies on the manifestation of a dementia syndrome and the elimination of other relevant systemic and brain diseases for a diagnosis of AD, accommodates a number of genetically and clinically heterogeneous conditions, but cannot promote our understanding of the preclinical pathogenetic processes and their interaction. If new molecular biological discoveries cannot be integrated with this traditional clinico-pathological model, it may have outlived its usefulness.