Alzheimer's disease (AD) is a neurodegenerative disease that slowly and progressively destroys brain cells. As the most common cause of dementia, it affects 60-65% percent of people with dementia. It is named after German neurologist Aloïs Alzheimer, who in 1906 first described the symptoms as well as the neuropathological features of the disease, such as amyloid plaques and tangles in the brain. AD affects memory and cognitive function, which may, for example, over time lead to confusion, changes of mood and getting lost even in familiar places. It is neither infectious nor contagious.
Most often, AD dementia is diagnosed in people over 65 years of age. Early symptoms of AD dementia, such as memory issues and partial loss of certain cognitive abilities may go unnoticed at first, both by the people concerned and by their loved ones. As the disease progresses, however, the symptoms become more noticeable and can interfere with day-to-day life. Practical difficulties with daily tasks such as dressing, washing and eating gradually become more severe. Eventually, people with AD dementia need help and support from others to manage such tasks. AD dementia causes a general deterioration in health, including increased frailty, and is terminal. The most common cause of death is pneumonia because as the disease progresses the immune system deteriorates and weight loss usually occurs, which increases the risk of throat and lung infections. There is currently no known cure.
Nevertheless, significant progress in biomedical research has been made in the field of AD by renowned researchers and clinicians. These recent advances have led to a radical change in the way that AD is conceptualised. For example, in the past the term Alzheimer’s disease was considered practically synonymous with dementia. Nowadays, signs of abnormal changes in the brain associated with AD can be detected long before the occurrence of any symptoms of AD dementia and the term is no longer limited to the AD dementia stage.
Despite a few differences, two key research groups agree that AD should be considered as occurring along a continuum. Both groups also agree on the importance of biomarkers in the procedure leading to a potential diagnosis of AD dementia. In order to reach a consensus on the diagnostic criteria and harmonisation of standards for research, Dubois and colleagues (2010 & 2016) developed and recently revised a new consensus lexicon to unify all definitions, stages and processes. According to this new lexicon, the definition of AD has been extended to encompass the full spectrum of the disease, including both pre-dementia (preclinical and prodromal AD or MCI due to AD) and dementia phases. Its diagnosis can, through the identification of biomarkers, be established in vivo (i.e. in a living person).
 The first is the International Working Group (IWG and IWG2) led by Dubois et al. (2007, 2014 & 2016) and the second is the National Institute on Aging and the Alzheimer’s Association (NIA-AA) (see Jack et al., McKhann et al., Albert et al. and Sperling et al., all in 2011).