Alzheimer's disease AD is a neurodegenerative disease that usually starts slowly and progressively worsens. Although the speed of progression can vary, the average life expectancy following diagnosis is three to twelve years. The causes of Alzheimer's disease remain poorly understood.
The strongest genetic risk factor is from an allele of apolipoprotein E. These misfolded protein aggregates interfere with normal cell function, and over time lead to irreversible degeneration of neurons and loss of synaptic connections in the brain. No treatments can stop or reverse its progression, though some may temporarily improve symptoms.
As of , there were approximately 50 million people worldwide with Alzheimer's disease. Given the widespread impacts of Alzheimer's disease, both basic-science and health funders in many countries support Alzheimer's research at large scales. The course of Alzheimer's is generally described in three stages, with a progressive pattern of cognitive and functional impairment.
As the disease progresses so does the degree of memory impairment. The first symptoms are often mistakenly attributed to aging or stress. Subtle problems with the executive functions of attentiveness , planning , flexibility, and abstract thinking , or impairments in semantic memory memory of meanings, and concept relationships can also be symptomatic of the early stages of Alzheimer's disease.
If memory loss is the predominant symptom of MCI, it is termed amnestic MCI and is frequently seen as a prodromal or early stage of Alzheimer's disease. In people with Alzheimer's disease, the increasing impairment of learning and memory eventually leads to a definitive diagnosis. In a small percentage, difficulties with language, executive functions, perception agnosia , or execution of movements apraxia are more prominent than memory problems.
