Alzheimer's disease is a mental disorder that causes memory loss and other cognitive abilities serious enough to interfere with daily life. It is the most common form of dementia. Alzheimer's disease accounts for 65 to 80 percent of dementia cases. Alzheimer's disease is a progressive disease, where dementia symptoms gradually worsen over several years. In its early stages, memory loss is mild, but in the late-stage of Alzheimer's disease, individuals lose the ability to carry on a conversation and respond to their environment. Basically, symptoms usually develop slowly and get worse over time, becoming severe enough to interfere with daily tasks. No treatments stop or reverse its progression, though some may temporarily improve symptoms.