Alzheimer's brains have key genetic differences

by Bradley J. Fikes for U~T San Diego:

Alzheimer's patients have brains with significantly more genetic variation than normal brain, including extra copies of a gene linked to the disease, according to a study led by scientists at The Scripps Research Institute.

The finding may help scientists track down the mechanism that causes nearly all cases of Alzheimer's, a mechanism that is not well understood. And with a better understanding of the mechanism, a treatment for Alzheimer's might be developed, the scientists say.

A study led by TSRI professor Jerold Chun found that neurons in brains of Alzheimer's patients had significantly more copies of fragments from chromosome 21, but not more whole chromosomes.

The fragments carry the gene for APP, or amyloid precursor protein, which has been linked to Alzheimer's. Moreover, those with Down syndrome carry three copies of chromosome 21 throughout their body, and those with Down syndrome tend to develop Alzheimer's as they age.

The Alzheimer's brain cells also contain on average about 200 million extra base pairs, Chun said in a Wednesday interview. The researchers don't know where that extra DNA is from.

Variations within the genetic makeup of a single organism is called genetic mosaicism. Its presence in people has only been appreciated in recent years. The traditional assumption has been that the great majority of cells in humans are genetically identical.

This is the first time DNA variation in individual neurons has been linked to Alzheimer's disease, said Chun, the study's senior author. Chun is a professor at TSRI and at the institute's Dorris Neuroscience Center. Diane M. Bushman and Gwendolyn E. Kaeser, of Chun's lab, are the study’s co-first authors.

The study was published in the journal eLife. It examined post-mortem brains from 32 Alzheimer's patients and 21 non-Alzheimer's patients.

Source: http://bit.ly/1zhemOZ