Causes Alzheimer's Disease

In some rare cases, people develop Alzheimer's in their late 30s, 40s, or 50s. This form of the disease, called early-onset dominantly inherited Alzheimer's disease, always runs in families and is caused by a mutation in one of three genes that a person has inherited from a parent. An NIA-funded clinical study is underway to identify the sequence of brain changes in this form of early-onset Alzheimer's, even before symptoms appear.

For more information about early-onset Alzheimer's, view this webinar video, which discusses research in families in Colombia, South America. The webinar was hosted by the NIH Fogarty Center as part of its Brain Disorders in the Developing World program.

More than 90 percent of Alzheimer's cases occur in people age 60 and older. The development and progression of this late-onset form of the disease are very similar to what is seen in the early-onset form of the disorder. The causes of late-onset Alzheimer's are not yet known, but they are believed to include a combination of genetic, environmental, and lifestyle factors. The importance of any one of these factors in increasing or decreasing the risk of developing Alzheimer's differs from person to person-even between twins.

Much basic research in Alzheimer's disease has focused on genes that cause the early-onset form of the disease and on how mutations in these genes disrupt cellular function and lead to the disorder. Scientists hope that what they learn about early-onset Alzheimer's disease can be applied to the late-onset form of the disease.

Perhaps the greatest mystery is why Alzheimer's disease largely strikes people of advanced age. The single best-known risk factor for Alzheimer's is age, and studies show that the prevalence of the disease dramatically increases after age 70. Research on how the brain changes normally as people age will help explain Alzheimer's prevalence in older adults. Other risk factors for Alzheimer's may include cardiovascular disease, diabetes, depression, and certain lifestyle factors such as being physically inactive.