Long before memory loss and dementia take hold, the sticky material that builds up and leads to Alzheimer’s disease starts to accumulate in the olfactory bulb: the part of the brain that processes smell. Researchers at McGill University are hopeful that a simple smell test may help them sniff out people with Alzheimer’s earlier, initiating treatment before irreversible symptoms set in.
Many of the most promising Alzheimer’s drugs in development today are geared towards slowing down disease progression. This means that earlier diagnosis could soon help patients stall the disease before the impact on memory and cognition becomes noticeable.
John Breitner, study co-author and director of the Centre for Studies on Prevention of Alzheimer’s Disease at McGill University, says that delaying the onset of symptoms by five years would be enough to reduce their severity by over 50 percent.
While smell has been the focus of many studies on detecting early Alzheimer’s, this study is the first to show that worsening smell test scores correlate with increased biological markers of Alzheimer’s.
Breitner and his team used a multiple choice scratch-and-sniff smell test, asking participants to identify strong and distinctive scents like bubblegum, gasoline, and lemon. They recruited 300 people to take the test, all considered at high risk because one of their parents had been diagnosed with Alzheimer’s. Participants also took a standard cognition test to look for symptoms of Alzheimer’s.
At the same time, 100 participants also volunteered to have regular lumbar punctures, allowing the researchers to sample the cerebrospinal fluid that bathes the brain and spinal cord. These fluid samples were tested for Alzheimer’s biomarkers total tau and phospho-tau, and their ratios with beta-amyloid.
The study found that decreased ability to identify smells was associated with lower cognitive scores and older age. Lower smell test scores were also paired with increased presence of Alzheimer’s biomarkers in cerebrospinal fluid.
Loss of smell is also associated with other neurodegenerative diseases, such as Parkinson’s, and a smell test is simple, inexpensive, and non-invasive. More testing is still needed, and smell tests may never replace standard biomarker and cognition tests, but one day they may be robust enough to help identify high risk patients for an earlier diagnosis.
