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.
So what is this disease? Why is it becoming more common? And is there any hope?
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.
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.
But dementia has already claimed number one spot in some richer countries.
In England and Wales, one in eight death certificates cite dementia.
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.
"Dementia certainly is the biggest health challenge of our time," Hilary Evans, chief executive of the charity Alzheimer's Research UK, told the BBC.
"It's the one that will continue to rise in terms of prevalence, unless we can do something to stop or cure this disease."
As the disease progresses, people eventually need full-time care and the annual cost of looking after people with dementia is in the region of $1 trillion a year.
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.
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