Sense of smell may be the first to go in people who carry a gene variant that’s linked to the highest risk for Alzheimer’s disease, according to a new study.

People with the APOE e4 gene variant may lose their ability to detect odors prior to those who don’t carry the variant, the research found. It could be an early sign of the disease, the scientists behind the study say. The report was published Wednesday in Neurology.

“Testing a person’s ability to detect odors may be a useful way to predict future problems with cognition,” Matthew S. GoodSmith, MD, a resident physician at the University of Chicago, said in a statement. “While more research is needed to confirm these findings and determine what level of smell loss would predict future risk, these results could be promising, especially in studies aiming to identify people at risk for dementia early in the disease.”

Researchers looked at surveys conducted at home from 865 people twice, five years apart. They asked the subjects if they could detect an odor and identify the source of the odor. They also tested thinking and memory skills twice. Each participant had their DNA evaluated so the scientists knew who carried the APOE e4 gene. The study participants didn’t include people with severe dementia. 

People who had the APOE e4 gene variant were 37% less likely to have good odor detection than people without the gene at a single point in time. Between the ages of 65 and 69, people carrying the Alzheimer’s gene started being able to smell less. In fact, they could pinpoint 3.2 of the odors, compared to 3.9 in people without the gene.

The people with the gene variant didn’t demonstrate a difference in their ability to identify what odor they were smelling until they were 75 to 79 years old. Once their odor-identification skills declined, their ability to detect odors decreased more quickly than those without the gene. Just like with odor skills waning, those with the gene had more rapid declines in thinking compared to those without the gene. 

“Identifying the mechanisms underlying these relationships will help us understand the role of smell in neurodegeneration,” GoodSmith said.

This adds to other research showing that loss of smell is tied to cognitive decline. Research out earlier this year found that having a good sense of smell is linked to slower brain volume loss and cognitive decline in older adults. Researchers found that the link between brain changes and scent may be significant in people with cognitive impairments or dementia. Scent issues also have been linked to depression later in life.