In the largest-ever genetic analysis of Alzheimer's, scientists have discovered 11 genes that may be tied to the late-onset form of the dementia disease.

Scientists scanned the brains of 74,076 older volunteers with Alzheimer's and others who did not have the disease in 15 countries to come up with their findings. The study was published in Nature Genetics.

Only 11 gene variants had been linked to late-onset Alzheimer's disease, including one called Apolipoprotein E-e4 (APOE-e4) which appeared to have the strongest effect on risk.

Now, with the latest research, scientists have doubled the known gene variants linked to the disease to 22.

These genes may play a role in how cells function, including how microglial cells (cells that form the support structure of the central nervous system) react to areas of inflammation. Other gene variants were shown to affect brain cell function and synaptic function in the hippocampus, which is the area of the brain responsible for memory and learning.

In particular, researchers say the link to one newly discovered gene variant known as HLA-DRB5/DRB1 is a landmark finding. It plays a large role in the major histocompatibility complex region of the brain, which is an area of cell surface molecules that control how white blood cells -- which are involved in the immune system -- interact. This area of the brain has also been connected with multiple sclerosis and Parkinson's disease. It could mean that the immune system has something to do with Alzheimer's.

"We've doubled the number of genes discovered and a very strong pattern is emerging," Julie Williams, a professor at the Neuroscience and Mental Health Research Institute at Cardiff University who lead part of the international study, told the BBC. "There is something in the immune response which is causing Alzheimer's disease and we need to look at that."

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