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An analysis of the Global Burden of Disease (GBD) study showed that migraine and headache disorders were leading causes of years lived with disability, and that for individuals aged 15–49 years, migraine is the leading cause of disability for women.

While the most prominent risk factor for AD is increasing age, the disease develops as a result of several risk factors that converge. Environmental factors also contribute to the development of dementia.

Microglial cells are activated by Aß deposits. Continuation of Aß deposition reduces the efficiency of microglial cells, which leads to neuroinflammation. The colocalization of Aβ, tau, and activated microglia in the brain potentiates tau propagation.

The staging method developed by Braak and Braak suggests that the neurofibrillary pathology of AD progresses in a relatively predictable sequence.

The symptoms of AD can be generally divided into three categories – cognitive, functional, and neuropsychiatric.

A variation to the clinical staging of AD was proposed by the National Institute on Aging – Alzheimer’s Association (NIA-AA) working group (2018) using six clinical stages for persons who are amyloid positive.