Brain to Z: D is for dementia

D is for dementia.

Dementia is an umbrella term for a group of symptoms that affect our cognitive abilities.

People are mostly familiar with its impact on memory, but dementia can also change the way someone thinks and behaves: someone may start experiencing hallucinations, for example, or lose interest in socialising.

It’s normal for our cognitive abilities to change as we age, but dementia is more severe than occasionally forgetting something. People with dementia can’t carry out ordinary tasks of the day without help, and their symptoms are progressive, which means they will get worse over time.

Dementia is not a disease itself. Instead, it is caused by diseases that damage the brain. 55 million people worldwide are thought to be affected.

Alzheimer’s disease is cited as being responsible for 70% of dementia cases. Its causes are complex, but a key element is the build-up of misfolded proteins in the brain, one of these a form of amyloid. If these substances clump together, they form plaques and tangles which disrupt the normal functions of brain cells.

In 2022, putting an end to decades of failure, the first drug treatment for Alzheimer’s showed success in slowing cognitive decline in large scale trials. Lecanemab works by attaching itself to sticky beta amyloids which have collected around the neurons of Alzheimer’s patients. Then, it attracts the body's immune cells to break down the harmful clumps.

While the effect of lecanemab was recorded as statistically significant, it is still relatively small.

There are also those who say the benefits of lecanemab do not counterbalance the risk of serious side effects like bleeding and swelling in the brain. It’s also extremely expensive, costing about £20,000 per patient per year in the US.

Writing in The Journal of the Alzheimer's Association, Carol Brayne, Professor of Public Health Medicine from the University of Cambridge says that, “While the current amyloid immunotherapies may show a glint of promise for very selected groups, it’s clear these drugs will not address dementia risk at scale.”

A sobering conclusion, and recently The European Medicines Agency has rejected a licence for the drug, but the US Food and Drug Administration has licenced lecanemab, and another amyloid immunotherapy, donenemab.

Despite this, the fact that it works at all has been seen as a huge step forward in treating Alzheimer’s by some. Here’s Will McEwan from Cambridge University’s UK Dementia Research Institute speaking on the Naked Scientists…

'These are not the ideal drugs. These are not the drugs that will be prescribed in 20 or 30 years, but they will be the turning point. They'll be seen as the moment where we know that this is ultimately a treatable disease.'