Lifewatch: Family history could reveal Alzheimer's Disease

Reported by Claire Hosmann - email
Posted by Debra Worley - email

(WECT) - 5.2 million Americans are living with Alzheimer's Disease, and half a million of those people are under the age of 65.

The deadly diagnosis slowly robs people of the ability to think, speak, and function.

Doctors say digging into your family history could help predict the future, but the answers aren't always easy to find.

Chuck Jackson has early onset Alzheimer's, a disease that claimed his mother, brother, grandfather, a dozen aunts and uncles, and a growing list of cousins.

Chuck uses his good moments to speak out against the Alzheimer's stigma.  He lobbies for more money and research on the disease.

"[I'm] Trying to help other people rather than hiding in the house saying it's not happening," said Chuck.

Chuck's family passed down a rare genetic mutation that damages a critical protein in the brain, causing early onset Alzheimer's.  It strikes people as young as 30.

About 90% of Alzheimer's cases are late-onset.  There is a genetic test to find out if a person is at risk for this type, but it can't tell you with certainty if you're going to get the disease.

A genetic test for the disease costs anywhere from $400 to several thousand dollars.  Experts ure people to talk to a genetic counselor about the emotional and mental toll before going through with the test.

The National Institute on Aging recently launched two large Alzheimer's genetics studies.

It's collecting and analyzing blood samples from thousands of families around the world who do and do not have late-onset Alzheimer's.

The goal is to study 10,000 samples and identify more risk factors in the next five years.

For more information, please contact:
Alzheimer's Association
(800) 272-3900

BACKGROUND: According to the National Institutes of Health, three-quarters of those who develop Alzheimer's disease (AD) have no family history of the disease; but for the rest, researchers say several genes may contribute to their disorder. AD is an irreversible and progressive condition. It is characterized by inflammation and buildup of amyloid plaque and neurofibrillary tangles in the brain, leading to nerve cell damage. There are two types of AD: early-onset and late-onset, both of which have genetic links.

LATE-ONSET: THE GENETIC LINK: According to the Alzheimer's Association, late-onset is the most common form of Alzheimer's disease and occurs in individuals 65 or older. The most common gene linked to this type of AD is apolipoprotein E (APOE). There are three APOE variations of the gene. APOE e2 occurs least often and appears to reduce the risk of Alzheimer's. APOE e3 is the most common variant and is not believed to affect a person's risk of getting the disease. APOE e4, however, appears to contribute to Alzheimer's. A person may carry two different types of the APOE gene, inheriting one from their mother and another from their father. Therefore, a person can have two APOE e4 genes, which puts them at an even greater risk of developing Alzheimer's.

Other studies link late-onset Alzheimer's to the gene SORL1. One study shows a variation of SORL1 is associated with a three times greater risk of developing AD in Dominican families. Certain variations of the SORL1 increase the production of amyloid-beta, which contributes to the formation of amyloid plaques in the brain. No specific mutation has been identified so far, but researchers say a potential treatment could be to target the gene and increase the production of the SORL1 receptor.

In June of 2008, researchers discovered another gene that increases the risk of late-onset Alzheimer's disease. Having one copy of calcium homeostasis modulator 1 (CALHM1) increases the chance of developing late-onset AD by 44 percent, while having two copies increases it by 77 percent. According to Philippe Marambaud, Ph.D., study author and an assistant professor at The Feinstein Institute for Medical Research in Manhasset, N.Y., roughly a quarter of the population has one copy of the gene. The CALHM1 gene regulates specific calcium channels in the brain, which permit electrically charged calcium molecules to enter cells and trigger production of beta amyloid proteins. Drugs that target calcium channels currently exist; however, none are designed to target the channels the CALHM1 gene controls.

EARLY-ONSET: THE GENETIC LINK: Less than 10 percent of AD sufferers have the early-onset variety, of which three genes have been linked to. Inheriting just one of these mutated genes almost guarantees the disease will strike before you turn 65. Amyloid precursor protein (APP), presenilin 1 (PS1) and presenilin 2 (PS2) all cause too much amyloid-beta peptide to be produced in the brain.

Roughly half of early-onset patients don't present any of these three genetic abnormalities, which means the aggressive version of AD may be caused by other genetic mutations that haven't been discovered.