Alzheimer's disease (AD) is a progressive degenerative disease of the brain, and the most common form of dementia. Some things you should know about Alzheimer's disease: Approximately 4 million Americans have AD. In a 1993 national survey, 19 million Americans said they had a family member with AD, and 37 million said they knew someone with AD. 14 million Americans will have AD by the middle of the next century unless a cure or prevention is found. One in 10 persons over 65 and nearly half of those over 85 have AD. A small percentage of people as young as their 30's and 40's get the disease. A person with AD will live an average of 8 years and as many as 20 years or more from the onset of symptoms. U.S. society spends at least $100 billion a year on AD. Neither Medicare nor most private health insurance covers the long term care most patients need. More than 7 of 10 people with Alzheimer's disease live at home. Almost 75% of the home care is provided by family and friends. The remainder is "paid" care costing an average of $12,500 per year. Families pay almost all of that out-of-pocket. Half of all nursing home residents suffer from AD or a related disorder. The average cost for nursing home care is $42,000 per year but can exceed $70,000 per year in some areas of the country. The average lifetime cost per patient is $174,000. Alzheimer's disease is the third most expensive disease in the United States, after heart disease and cancer. The federal government will spend approximately $309 million for Alzheimer's disease research in 1996. This represents $1 for every $324 the disease now costs society. The federal investment in heart disease, cancer, and AIDS is four to seven times higher.