Alzheimer's disease (AD) is a neurodegenerative disease that usually starts slowly and progressively worsens. It is the cause of 60–70% of cases of dementia. The most common early symptom is difficulty in remembering recent events. As the disease advances, symptoms can include problems with language, disorientation (including easily getting lost), mood swings, loss of motivation, self-neglect, and behavioral issues. As a person's condition declines, they often withdraw from family and society. Gradually, bodily functions are lost, ultimately leading to death. Although the speed of progression can vary, the typical life expectancy following diagnosis is three to nine years. The disease is named after German psychiatrist and pathologist Alois Alzheimer, who first described it in 1906. Alzheimer's financial burden on society is large, with an estimated global annual cost of US$1 trillion. Alzheimer's disease is currently ranked as the seventh leading cause of death in the United States. No treatments stop or reverse its progression, though some may temporarily improve symptoms More than 6 million Americans, many of them age 65 and older, are estimated to have Alzheimer’s disease. That’s more individuals living with Alzheimer’s disease than the population of a large American city. Many more people experience Alzheimer's in their lives as family members and friends of those with the disease. The symptoms of Alzheimer’s disease — changes in thinking, remembering, reasoning, and behavior — are known as dementia. That’s why Alzheimer’s is sometimes referred to as “dementia.” Other diseases and conditions can also cause dementia, with Alzheimer’s being the most common cause of dementia in older adults. Alzheimer’s disease is not a normal part of aging. It’s the result of complex changes in the brain that start years before symptoms appear and lead to the loss of brain cells and their connections. The course of Alzheimer's is generally described in three stages, with a progressive pattern of cognitive and functional impairment. The three stages are described as early or mild, middle or moderate, and late or severe. The disease is known to target the hippocampus which is associated with memory, and this is responsible for the first symptoms of memory impairment. As the disease progresses so does the degree of memory impairment.