Confusing the smells of petrol and bubblegum could be an early sign of dementia

Being unable to differentiate between the smell of petrol and the odour associated with bubblegum could be an early sign of dementia. According to a new study carried out by scientists at McGill University in Canada, changes to the sense of smell could be an early warning of the disease.

Such a breakthrough could be significant, as, at present, there is no way to know that the brain is being damaged by Alzheimer’s in its early stages. It can take up to 20 years for the symptoms to show and by then, the condition has already taken hold.

Researchers tested the theory that damage to the olfactory neurons is one of the first side effects to occur when Alzheimer’s begins. In the study, 300 people with a predisposition to the disease were asked to identify different scratch-and-sniff smells. These scents were particularly strong and included the odours of petrol, bubblegum and lemon.

Regular lumbar punctures were also carried out on 100 of the volunteers, in order to monitor the levels of AD-related proteins in the cerebrospinal fluid (CSF). It is the build-up of these proteins or plaques that is thought to create the problems suffered by those with Alzheimer’s.

The scientists discovered that the individuals who had the most difficulties in identifying the different smells were the ones where biological indicators of Alzheimer’s disease were present. Early warning signs make it easier to treat the condition before it has had a chance to affect everyday life.

Marie-Elyse Lafaille-Magnan, a doctoral student at McGill and the first author on the study, said: “This is the first time that anyone has been able to show clearly that the loss of the ability to identify smells is correlated with biological markers indicating the advance of the disease.

“For more than 30 years, scientists have been exploring the connection between memory loss and the difficulty that patients may have in identifying different odours.

“This makes sense because it’s known that the olfactory bulb, involved with the sense of smell and the entorhinal cortex, involved with memory and naming of odours, are among the first brain structures first to be affected by the disease.”

It is thought that some 800,000 people in the UK are currently living with dementia and Alzheimer’s is the most common form of the disease. At present, there is no cure for the condition and drugs to minimise its impact are usually prescribed too late, once symptoms have developed and the irreversible damage to the brain already occurred.

A smell test, if proven to be effective, could be a quick and inexpensive way to detect the disease before it gets to that point. Dr John Breitner, the director of the Centre for Studies on Prevention of Alzheimer's Disease at the Douglas Mental Health Research Centre of McGill University, believes it could be an important step forward.

He has said that delaying the onset of symptoms by as little as five years could reduce the prevalence of the condition, as well as its severity, by as much as 50 per cent. This would allow many people, especially the elderly, to maintain their independence for longer.