An anonymous reader quotes a report from the Guardian: The largest genetic study of Alzheimer’s to date has provided compelling evidence linking the disease to disruption in the brain’s immune system. The study, using the genomes of 100,000 people with Alzheimer’s and 600,000 healthy people, identified 75 genes linked to an increased risk of the disease, including 42 that had not previously been implicated. The findings suggest degeneration in the brains of dementia patients could be spurred on by “over-aggressive” activity in the brain’s immune cells, called microglia.

The study, the largest of its kind to date, also allowed scientists to devise a genetic risk score that could predict which patients with cognitive impairment would, within three years of first showing symptoms, go on to develop Alzheimer’s. The score is not intended for clinical use at the moment, but could be used when recruiting people for clinical trials of drugs aimed at treating the disease in the earliest stages. The latest work highlights different sets of genes seen in more common forms of Alzheimer’s, including a role for the immune system. “If [at the outset] we’d seen the genetics of common disease, we would’ve said this is an immune disease,” said professor Julie Williams, the director of the UK Dementia Research Institute at Cardiff University and a co-author of the study. “It’s not the same disease.”

Risk genes highlighted in the study include ones that affect how efficiently the brain’s immune cells, microglia, clear away tissue that is distressed. In people at risk, these housekeeper cells appeared to be working too aggressively. A similar pattern was found for genes that control how readily synapses, which connect neurons, send out an “eat me” signal when in distress. The high-risk variants appeared to lower the threshold for synapses sending out distress signals, causing the brain to purge connections at a quicker rate. The findings, published in the journal Nature Genetics, fit with previous results pointing to a role for the immune system. People with diabetes, which affects the immune system, are at considerably higher risk, for instance, and once dementia has been diagnosed infections can trigger more rapid cognitive decline.

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Source: Slashdot – Alzheimer’s Study Finds 42 More Genes Linked To Higher Risk of Disease