The Connection between Down Syndrome and Alzheimer’s Disease
Many, but not all, people with Down syndrome develop Alzheimer’s disease when they get older. Alzheimer’s is an irreversible, progressive brain disorder that slowly destroys memory and thinking skills and, eventually, the ability to carry out simple tasks.
Alzheimer’s disease is the most common cause of dementia among older adults. Dementia is the loss of cognitive functioning—thinking, remembering, and reasoning—and behavioral abilities to such an extent that it interferes with a person’s daily life and activities.
People with Down syndrome are born with an extra copy of chromosome 21, which carries the APP gene. This gene produces a specific protein called amyloid precursor protein (APP). Too much APP protein leads to a buildup of protein clumps called beta-amyloid plaques in the brain. By age 40, almost all people with Down syndrome have these plaques, along with other protein deposits, called tau tangles, which cause problems with how brain cells function and increase the risk of developing Alzheimer’s dementia.
However, not all people with these brain plaques will develop the symptoms of Alzheimer’s. Estimates suggest that 50 percent or more of people with Down syndrome will develop dementia due to Alzheimer’s disease as they age, many now into their 70s.