Dementia describes a group of symptoms associated with a decline in memory, reasoning or other thinking skills. Many different types of dementia exist, and many conditions cause it. Mixed dementia is a condition in which brain changes of more than one type of dementia occur simultaneously. Alzheimer's disease is the most common cause of dementia, accounting for 60-80% of dementia cases. Dementia is not a normal part of aging. It is caused by damage to brain cells that affects their ability to communicate, which can affect thinking, behavior and feelings.
Though the greatest known risk factor for Alzheimer's is increasing age, the disease is not a normal part of aging. And though most people with Alzheimer's are 65 and older, approximately 200,000 Americans under 65 are living with younger-onset Alzheimer's disease.