Nearly everyone with Alzheimer’s disease will eventually have the same symptoms -- memory loss, confusion, trouble with once-familiar tasks, and making decisions. While the manner of the disease development remains unclear, all forms of Alzheimer's appear to share overproduction and/or decreased clearance of a type of protein called amyloid beta peptides. Though the effects of the disease are similar, there are two main types.
Early-onset Alzheimer's. This type happens to people who are younger than age 65. Often, they’re in their 40s or 50s when they’re diagnosed with the disease. It’s rare -- up to 5% of all people with Alzheimer's have early-onset. People with Down syndrome have a higher risk for it.
Scientists have found a few ways in which early-onset Alzheimer’s is different from other types of the disease. People who have it tend to have more of the brain changes that are linked with Alzheimer’s. The early-onset form also appears to be linked with a defect in a specific part of a person’s DNA: chromosome 14. A form of muscle twitching and spasm, called myoclonus, is also more common in early-onset Alzheimer's.
- Late-onset Alzheimer's. This is the most common form of the disease, which happens to people age 65 and older. It may or may not run in families. So far, researchers haven’t found a particular gene that causes it. No one knows for sure why some people get it and others don’t.
Familial Alzheimer's disease (FAD) is a form of Alzheimer's disease that doctors know for certain is linked to genes. In families that are affected, members of at least two generations have had the disease. FAD makes up less than 1% of all cases of Alzheimer's. Most people who have early onset Alzheimer's have FAD.