The sixth leading cause of death in the US, Alzheimer's disease is believed to currently affect 5.3 million Americans, according to the Centers for Disease Control and Prevention (CDC). One tenth of people aged over 65 have the condition.
Published in the journal Nature Neuroscience, the researchers claim the new research is the first large-scale study to look at chromosomal make-up in relation to the brain and Alzheimer's disease.
"Our study approach may help us to better understand the biological impact of environmental risk factors and life experiences on Alzheimer's disease," says lead study author Dr. Philip L. De Jager, from Brigham and Women's Hospital's Departments of Neurology and Psychiatry.
"There are certain advantages to studying the epigenome, or the chemical changes that occur in DNA. The epigenome is malleable and may harbor traces of life events that influence disease susceptibility, such as smoking, depression and menopause, which may influence susceptibility to Alzheimer's and other diseases."
The team analyzed samples from 708 donated brains in the Religious Orders Study and Rush Memory and Aging Project.
CpG markers and Alzheimer's
The researchers were particularly interested in CpG markers - pairs of DNA building blocks consisting of a cytosine and guanine nucleotide located next to each other. Examining the donated brain samples, the researchers found that 71 of the 415,848 CpG markers they analyzed correlated with Alzheimer's disease.
"Our work has helped identify regions of the human genome that are altered over the life-course in a way that is associated with Alzheimer's disease," claim the researchers.
The 71 markers were located in the ANK1, RHBDF2, ABCA7 and BIN1 genes, some of which have been previously associated with gene variants implicated in Alzheimer's risk.
Looking more closely at the CpG markers, the team also discovered nearby genes that exhibited altered RNA expression in the brain samples from Alzheimer's patients. These genes are ANK1, CDH23, DIP2A, RHBDF2, RPL13, RNF34, SERPINF1 and SERPINF2.
"It appears that these DNA methylation changes may play a role in the onset of Alzheimer's disease," says Dr. De Jager.
"Moreover," he says, "our work has helped identify regions of the human genome that are altered over the life-course in a way that is associated with Alzheimer's disease. This may provide clues to treating the disease by using drugs that influence epigenomic function."
Recently, Medical News Today reported on a study that found an association between vitamin D deficiency and dementia.
Participants in that study who had low levels of vitamin D were calculated as having a 70% increased risk of developing Alzheimer's disease. Participants with severe vitamin D deficiency, meanwhile, had an increased risk of 120%, compared with study participants who had normal levels of vitamin D.
Another recent study, published in the journal Neurology, suggested that depression in later life may increase risk of mild cognitive impairment - a condition that is a common precursor to Alzheimer's.