Boston scientists have developed a diagnostic test that might someday literally sniff out Alzheimer’s disease in high-risk groups.

A team of researchers led by Dr. Mark Albers, a neurologist at Massachusetts General Hospital, recruited 183 older patients with varying degrees of cognitive health. The volunteers underwent a series of tests that measured their ability to identify, recall, and distinguish between odors, such as one that asked them to decide whether two consecutive smells were the same or different. Their overall performance correlated with their level of cognitive decline, the researchers found. For instance, people in normal health generally fared better than people with no measured decline but who were worried about their cognitive ability, who in turn were better than volunteers with mild cognitive decline, and they were better than people with suspected full-blown Alzheimer's.

The team’s findings were published Monday in the Annals of Neurology.

“There is increasing evidence that the neurodegeneration behind Alzheimer’s disease starts at least 10 years before the onset of memory symptoms,” said Albers in a statement. “The development of a digitally-enabled, affordable, accessible and non-invasive means to identify healthy individuals who are at risk is a critical step to developing therapies that slow down or halt Alzheimer’s disease progression.”

The hunt for an accurate early diagnostic test has been one of the holy grails of Alzheimer’s research. Currently, doctors can only indirectly diagnose the condition in still-living patients, and usually only after some amount of cognitive decline has already occurred. Genetic factors, like having the E4 version of the APOE-gene, are known to increase the risk of Alzheimer’s as well, but they’re far from a surefire means of detection.

Because our ability to recall and identify smells — what scientists call the olfactory system — is known to decline along with our memories as we develop Alzheimer’s, though, researchers have theorized that our noses could serve as an early warning. Elsewhere, a study detailed by Medical Daily earlier this July found a similar link between a poor sense of smell and dementia risk. Like the current study, the researchers also found that these scores correlated with the thinning of brain regions affected earliest by Alzheimer’s. And while our sniffing prowess differs greatly from person to person regardless of Alzheimer’s risk, Alber’s team found that poor odor recallers were more likely to have the APOE gene as well.

Next on the agenda for Albers’ team is finding more volunteers for a larger study that can hopefully reaffirm their current findings.

“It is well recognized that early diagnosis and intervention are likely to produce the most effective therapeutic strategy for Alzheimer’s disease – preventing the onset or the progression of symptoms,” he said. “If these results hold up, this sort of inexpensive, noninvasive screening could help us identify the best candidates for novel therapies to prevent the development of symptoms of this tragic disease.”

Source: Albers A, Asafu-Adjei J, Delaney M, et al. Episodic Memory of Odors Stratifies Alzheimer Biomarkers in Normal Elderly. Annals of Neurology. 2016.