The study, published in January 2017 in JAMA Neurology journal, suggests that early risk factors for developing the disease are linked to changes in myelin.

Myelin changes in Alzheimer's are suspected by many researchers but have been understudied in humans. "The results from this paper suggest that those changes may play a key role in the onset of the disease," says Asthana, head of the Geriatric, Research, Education, and Clinical Center at the William S. Middleton Memorial Veterans Hospital in Madison, Wisconsin.

According to Asthana, the idea that myelin is involved in Alzheimer's can be traced back several decades to two German doctors who studied degenerative changes in the brain. Heiko Braak and Eva Braak analyzed brains after people died and found that regions that developed myelin later in life were also areas that were first affected by Alzheimer's.

More recently, Alzheimer's research by another co–author of Asthana's study, Dr. Barbara Bendlin of the University of Wisconsin, found through brain scans of middle–aged and older adults that white matter seemed to be damaged. "No one had shown that relationship in living humans before Dr. Bendlin published her paper," Asthana says. "That brought attention to the possibility that white matter changes may be very important in causing Alzheimer's. We wanted to see if this damage is related or unrelated to Alzheimer's disease pathology."

Asthana's study included 71 healthy participants – 52 women and 19 men – ranging in age from 48 to 72. The average age was 61.6.

The participants were Alzheimer's asymptomatic but at high risk for the disease because at least one of their parents had it. Asthana explains that any person with Alzheimer's can show changes in myelin regardless of their parents' history with the disease, but that people with a family history are at much higher risk of such changes. His chances of getting Alzheimer's, for example, are up at least 30 percent because his father had the disease, he says. The researchers used a novel MRI technique that makes it easier to analyze the quantity of myelin content. They tested the participants for four cerebrospinal fluid (CSF) biomarkers consistent with signs of Alzheimer's (beta–amyloid 42, total tau protein, phosphorylated tau 181, soluble amyloid precursor protein). The CSF, which is in the brain and spine and acts as a cushion for the brain's cortex, was extracted with lumbar punctures.

The scientists found widespread changes in myelin content associated with increasing age, including in areas of the brain such as the frontal white matter. The findings showed "for the first time to our knowledge," the researchers write, that lower concentrations of beta–amyloid 42 and higher concentrations of total tau protein, phosphorylated tau 181, and soluble amyloid precursor protein, and their ratios with beta–amyloid 42, are closely linked to changes in myelin content.

"Furthermore, we show that the age–related decline in myelin content is influenced by the levels of CSF biomarkers," the researchers explain.

Asthana and his colleagues were surprised by the findings partly because in Alzheimer's research the widely held assumption is that everything takes place in the gray matter of the brain, not in white matter. "So this in some way established that that is not true," he says.

Clarifying the extent of myelin damage in preclinical Alzheimer's may be informative in understanding the course of the disease and may lead to new biomarkers for prevention and treatment trials, according to the study.

Asthana says any future treatments for myelin changes may be in the form of drugs, but that simply maintaining a healthy diet and lifestyle will be important, too.