Alzheimers: Introduction Alzheimer's disease (AD) affects the mental abilities including memory, language, and cognition. Progressively it leads to dementia and death. AD usually arises in late middle age or the elderly but there is a rare familial subtype that occurs earlier. Because AD is so well-known, other causes of dementia or memory loss may be overlooked. Other possible diagnoses include normal aging (if very mild symptoms), emotional problems, fatigue, depression, and certain medical conditions such as thyroid disease, brain tumors, multi-infarct disease, or Huntington's disease. In its early stages, a correct diagnosis of AD can also be overlooked itself and misdiagnosed as other conditions such as depression, dementia, simple forgetfulness, or senility.