Dementia: The greatest health challenge of our time
Ageing is the biggest risk factor for developing dementia.
Dementia is the greatest health challenge of our time, the charity Alzheimer's Research UK has warned.
Dementia was first described by the German doctor Alois Alzheimer in 1906 after he performed an autopsy on a woman with profound memory loss.
What he found was a dramatically shrunken brain and abnormalities in and around nerve cells.
At the time dementia was rare and was then barely studied for decades.
But today somebody is diagnosed with it every three seconds, it is the biggest killer in some wealthier countries and is completely untreatable.
Is dementia the same as Alzheimer's?
No - dementia is a symptom found in many diseases of the brain.
Memory loss is the most common feature of dementia, particularly the struggle to remember recent events.
Other symptoms can include changes to behaviour, mood and personality, becoming lost in familiar places or being unable to find the right word in a conversation.
It can reach the point where people don't know they need to eat or drink.
Alzheimer's disease is by far the most common of the diseases that cause dementia.
Others include vascular dementia, dementia with Lewy bodies, fronto-temporal dementia, Parkinson's disease dementia, amyotrophic lateral sclerosis and the newly discovered Late.
New type of dementia discovered
Is it really the biggest health problem of our time?
Globally around 50 million people are currently living with dementia.
But cases are predicted to soar to 130 million by 2050 as populations age.
According to the World Health Organization, deaths from dementia have doubled since 2000 and dementia is now the fifth biggest killer worldwide.
There is also a key difference with other major killers such as cancer or heart disease, because there is not a single treatment that either cures or slows the pace of any dementia.
Why is it becoming more common?
The answer is simple - we are living longer and the biggest risk factor for dementia is age.
That is why huge increases in dementia cases are predicted for Asia and Africa.
With a more philosophical hat on, you can see dementia as the price we pay for progress in treating deadly infections, heart attacks and cancer.
Although there is an unexpected and hopeful trend emerging that has surprised some in the field - the proportion of elderly people getting dementia is falling in some countries.
Studies have shown the dementia rate (the number of cases per 1,000 people) falling in the UK, Spain and the US and stabilising in other countries.
This is largely being put down to improvements in areas like heart health and education which in turn benefit the brain.
Why do trials of drugs keep failing?
Be in no doubt - even a drug that just slows the progression of dementia would make someone a fortune.
It is not for the want of trying that there is no treatment for dementia.
Aducanumab, a drug that many hoped would work in Alzheimer's disease, is just the latest to fall by the wayside.
In March this year, Biogen and Eisai announced their drug was unlikely to be effective and ended the trial early.
Aducanumab, like those that have failed before, had been designed to target a toxic protein called amyloid beta that builds up inside the brain of patients with Alzheimer's disease.
If you go back to Dr Alzheimer in 1906, then some of the abnormalities he found in that brain autopsy were plaques of amyloid beta.
So a clear connection between amyloid beta and Alzheimer's emerged and the assumption was that the protein was killing brain cells.
Therefore removing amyloid beta should save brain cells and slam the brakes on Alzheimer's, experts thought.
Has science made a massive, expensive mistake? Is the "amyloid hypothesis" dead? These are questions being asked.
Prof Bart De Strooper, the director of UK Dementia Research Institute, told me: "The amyloid hypothesis as has been formulated over the last 20 years is dead, that I would accept.
"What I won't accept is that the importance of amyloid is dead."
A new theory for Alzheimer's?
Some researchers are pinning hopes on another protein called tau.
If amyloid beta is the trigger, tau may be the bullet.
Focusing on neurones and dangerous proteins can miss the bigger picture of what is happening in the brain.
This is a lesson being learned from cancer, where understanding the role the immune system plays has led to a whole new branch of medicine - cancer immunotherapy.
The immune system is being heavily implicated in dementia too.
If you look at genetic mutations that increase the risk of developing dementia, then a good chunk of them are involved in the immune system.
While your brain is packed with neurones that do the "thinking" - they are ably assisted by special immune cells called microglia.
They do fight infections, but also keep the brain running smoothly by munching up anything that should not be there.
And the blood vessels in the brain are increasingly being seen as a key player, not just in vascular dementia, but other dementias too.
Prof De Strooper still sees abnormal proteins as the trigger, but "then you have the response of the brain on that threat".
Prof De Strooper said: "All of a sudden, you open a broad box of possible drug targets, because you can then start to think about how do we improve the response of the brain at the inflammatory side, at the vascular side, at the neuronal side?
Well how will treatments work then?
Let's fast forward to a world where we do have treatments and now the brain's great asset, its adaptability, is the problem as it may have masked the disease for more than a decade.
Ms Evans, from Alzheimer's Research UK, said: "There's no point halting the progression of the disease in end stage disease."
But equally it will not be practical for everybody to have a regular brain scan to catch dementia early, because those scans are incredibly expensive.
One option is the approach taken in heart disease, where millions of people take pills to lower cholesterol levels in order to stop their arteries being clogged up.
Statins lower risk before people have a medical problem.
Prof de Strooper envisages a system of screening people that may even start at birth with a DNA test that predicts who is at greater risk.
Is there anything I can do to dodge dementia?
Or do they prepare the brain for dementia by increasing the connections and flexibility of the brain so that as neurones start to die, the brain can compensate for longer and symptoms don't emerge?
On a personal level it probably doesn't matter - not getting dementia, is not getting dementia. But scientifically the questions matter as the answers will illuminate what is going on in the brain.
"People who are very healthy and take good care of themselves are the group that I would say is most resilient to Alzheimer's disease," says Prof Spires-Jones.
So is there any hope?
There is now far more money being spent on dementia research.
The optimistic view is that we are at the same point as the Aids crisis was in the 1980s, when an HIV infection was a death sentence.
But now people who get anti-viral drugs have a nearly normal life expectancy.
Prof Spires-Jones said: "We know from things like cancer, that if you do a lot of science and research into a field, you can make a huge difference and find cures and treatments for these complex diseases. -BBC