However, evidence from multiple research groups is converging towards this conclusion.
"During the aging process ... some genes need to be turned on, and some turned off".
In people with Alzheimer's disease, tau tangles tend to emerge in parts of the brain important for memory-the hippocampus and entorhinal cortex-and then spread to other brain regions.
When we're awake, we keep the neurons within our brains busily signaling and releasing a protein called tau. Previously, altered sleep patterns have been linked to increased levels of beta-amyloid. Another small study published in 2016 in the journal PLOS ONE found gum disease was associated with a six-fold increase in the rate of cognitive decline in people with mild to moderate dementia.
Much the same effect was seen in people.
Researchers at Shiley-Marcos Alzheimer's Disease Research Center, part of the University of California San Diego School of Medicine, found that autopsies of patients diagnosed with AD when they were alive-and confirmed by autopsy-indicate several cognitive issues symptomatic of the condition are less noticeable in living Latino patients.
The causes of Alzheimer's disease are still debated.
Jucker's team measured the rate of change in NfL using a blood test in 405 individuals from across the world enrolled in the Dominantly Inherited Alzheimer's Network - an worldwide research effort focused on dominantly inherited Alzheimer's disease, a rare form of the illness that represents less than 1% of all cases of Alzheimer's, according to the National Institute on Aging.
"There have been very few autopsy studies in Hispanic elderly with Alzheimer's disease that have allowed researchers to gain insight about factors that might make it more hard to clinically diagnose the disease in this demographic", said senior author David P. Salmon, PhD, professor in the Department of Neurosciences and Helen A. Jarrett Chair in Alzheimer's Research at UC San Diego School of Medicine.
We have another entry in the "Is Alzheimer's caused by infectious disease?" drawing, and it's a good one.
The researchers of this new study say one explanation for the link is that bacteria from gum disease may access the brain by infecting immune system cells or spreading through cranial nerves passing through the head and jaw.
Mice are nocturnal creatures and researchers found tau levels in the fluid surrounding brain cells were about twice as high at night, when the animals were more awake and active, than during the day, when the mice dozed more frequently. The result suggests the bacterium may play a role in driving the development of the disease, researchers reported yesterday (January 23) in Science Advances.
They add: "We also demonstrated [in living animals] that an orally-administered [gingipain] inhibitor is more effective than a high-dose subcutaneous broad spectrum antibiotic in clearing P. gingivalis from the brain". They did not resist the gingipain blockers. Each research organization was responsible for bringing in the trial's clinical patients and collecting the resources and data the USC team used to inform its findings.
In addition to Pg itself, the study team also detected the organism's toxic proteases, or gingipains, in the neurons of patients with AD.
"We now have strong evidence connecting P. gingivalis and Alzheimer's pathogenesis, but more research needs to be done before P. gingivalis is explicitly implicated in the causation or morbidity of Alzheimer's disease", said study co-author Jan Potempa.