Alzheimers 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 persons 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 cause of Alzheimers disease is poorly understood. There are many environmental and genetic risk factors associated with its development. The strongest genetic risk factor is from an allele of APOE. Other risk factors include a history of head injury, clinical depression, and high blood pressure. The disease process is largely associated with amyloid plaques, neurofibrillary tangles, and loss of neuronal connections in the brain. A probable diagnosis is based on the history of the illness and cognitive testing with medical imaging and blood tests to rule out other possible causes. Initial symptoms are often mistaken for normal aging. Examination of brain tissue is needed for a definite diagnosis, but this can only take place after death. Good nutrition, physical activity, and engaging socially are known to be of benefit generally in aging, and these may help in reducing the risk of cognitive decline and Alzheimers; in 2019 clinical trials were underway to look at these possibilities.
Spirochete infections have also been linked to dementia. DNA damages accumulate in AD brains; reactive oxygen species may be the major source of this DNA damage.Sleep disturbances are seen as a possible risk factor for inflammation in Alzheimers disease. Sleep problems have been seen as a consequence of Alzheimers disease but studies suggest that they may instead be a causal factor. Sleep disturbances are thought to be linked to persistent inflammation. The cellular homeostasis of biometals such as ionic copper, iron, and zinc is disrupted in Alzheimers disease, though it remains unclear whether this is produced by or causes the changes in proteins. Smoking is a significant Alzheimers disease risk factor. Systemic markers of the innate immune system are risk factors for late-onset Alzheimers disease. Exposure to air pollution may be a contributing factor to the development of Alzheimers disease.One hypothesis posits that dysfunction of oligodendrocytes and their associated myelin during aging contributes to axon damage, which then causes amyloid production and tau hyper-phosphorylation as a side effect. Retrogenesis is a medical hypothesis that just as the fetus goes through a process of neurodevelopment beginning with neurulation and ending with myelination, the brains of people with Alzheimers disease go through a reverse neurodegeneration process starting with demyelination and death of axons (white matter) and ending with the death of grey matter.