Young-onset Alzheimer's

A very small percentage of people who develop Alzheimer's disease have the young-onset type. Signs and symptoms of this type usually appear between ages 30 and 60 years. This type of Alzheimer's disease is very strongly linked to your genes.

Scientists have identified three genes in which mutations cause early-onset Alzheimer's disease. If you inherit one of these mutated genes from either parent, you will probably have Alzheimer's symptoms before age 65. The genes involved are:

• Amyloid precursor protein (APP)
• Presenilin 1 (PSEN1)
• Presenilin 2 (PSEN2)

Mutations of these genes cause the production of excessive amounts of a toxic protein fragment called amyloid-beta peptide. This peptide can build up in the brain to form clumps called amyloid plaques, which are characteristic of Alzheimer's disease. A buildup of toxic amyloid-beta peptide and amyloid plaques may lead to the death of nerve cells and the progressive signs and symptoms of this disorder.

As amyloid plaques collect in the brain, tau proteins malfunction and stick together to form neurofibrillary tangles. These tangles are associated with the abnormal brain functions seen in Alzheimer's disease.

However, some people who have early-onset Alzheimer's don't have mutations in these three genes. That suggests that some early-onset forms of Alzheimer's disease are linked to other genetic mutations or other factors that haven't been identified yet.

One of the active research trials is the Dominantly Inherited Alzheimer Network (DIAN), which studies individuals with dominant Alzheimer's mutations (PSEN1, PSEN2 or APP). This research network includes observational studies and clinical trials.