An extended family in Colombia struck by hereditary and very early onset Alzheimer's is taking part in a new drugs trial that doctors hope will lead to a cure for sufferers worldwide.
Johnhaider sits in a wheelchair, rubbing one leg compulsively. His eyes are empty. He can no longer talk. He doesn't know where he is. He doesn't know his sister Patricia.
Johnhaider is in the final stages of Alzheimer's disease - the most common form of dementia.
This is remarkable for two reasons. He is only 53, when most patients at the same stage of this terminal illness are in their mid-60s at least.
He is also a member of an extended Colombian family, half of whom will contract Alzheimer's at an early age, according to medical researchers who have been monitoring the occurrence of the disease in the clan.
There is now hope that research involving this family - who are described by one scientist as a "natural laboratory" - will help speed the discovery of a cure for this devastating condition.
The clan is currently about 5,000-strong and scattered across remote villages in the Andes mountains that surround the northerly city of Medellin - the second largest in Colombia. All are descendants of one couple of Basque origin, who settled here in the early 1700s.
The man responsible for uncovering this family's cruel medical history is Dr Francisco Lopera, a behavioural neurologist at Medellin's University of Antioquia.
Dr Lopera first stumbled on the phenomenon in the early 1980s.
"I saw a man of 47 with dementia that was very similar to Alzheimer's disease. That was curious because he was very young."
Then Dr Lopera learned that the man's father, grandfather and several brothers had also suffered from dementia.
"I saw we had three generations affected, and in each generation half of the children were affected. This was hereditary."
Dr Lopera and a small team from his university scoured the region, despite the risks from drug traffickers and rebels of the Revolutionary Armed Forces of Colombia (Farc).
By the end of the 1980s, he had assembled a family tree stretching back nearly 300 years, big enough to cover the wall of an auditorium.
It took another decade to isolate the cause - a gene thought to trigger early onset of the disease.
If one parent has the gene, there is a 50% chance their child will have it too. Half the Colombian family members carry the gene, called the paisa mutation - "paisa" refers to the people of the region.
This rare mutation in an isolated population has attracted scientists from the Banner Institute in Phoenix, Arizona - a world leader in dementia research.
Dr Adam Fleisher, a geriatric neurologist at the institute, says Alzheimer's is like "an approaching pandemic". With life expectancy increasing, and the number of dementia suffers growing exponentially, the disease has the potential to devastate public healthcare systems in developed countries, he says.
"The truth is it's going to affect you, and your ability to get healthcare, whether you get Alzheimer's or not. We need to find a cure."
The Banner Institute scientists will test drugs on the family which are designed to attack a neural plaque that builds up on the brains of all Alzheimer's sufferers. The sticky, chewing gum-like plaque is caused by a malfunction which causes the misproduction of a starch-like protein called amyloid.
The hope is that by using experimental drugs, growth of this amyloid plaque will be inhibited before the illness strikes.
The Colombian family present researchers with the chance to work with healthy people before they develop dementia.
Using lumbar punctures, brain scans and other techniques, they will monitor and measure those on the drugs and those receiving a placebo.
The hope is that with funding in place, the trials can begin in late 2012.
If in the extended family the onset of Alzheimer's is delayed, or stopped, then the researchers will have hit the mother lode - a potential cure for sufferers worldwide. That remains a big if.
No-one yet knows if amyloid plaque is the cause or an effect of Alzheimer's. As Joseph Arboleda, a Harvard-based researcher working with Dr Lopera says, the trial puts this hypothesis to the test.
It is possible that drugs will inhibit the brain plaque and yet the family will still get dementia. Such results would prove devastating for current research.
"It would be a huge setback for everybody," says Arboleda. "The patients, the scientists - this is the best we've got. If it falls down everyone is in trouble."
For the family, though, the burden of care, the terrible knowledge that for half of them the disease is inevitable, and that the paisa mutation will be passed on to half of their children far outweighs the risk of trialling unproven drugs.
Johnhaider was in his mid-40s when the symptoms first struck, and by that time his mother had already died from the disease. She too had begun to exhibit symptoms in her mid-40s.
Johnhaider's sister, Patricia, does not know if she carries the gene. At 49, and with no signs yet, she is hopeful but worried, and that is why she is prepared to take part in the trial.
"I have no options," she says, gently adjusting a worn blanket that covers her brother's thin legs.
"I am a little bit worried," says Patricia. "But I want to participate: it's for me, it's for my family, and it's for the rest of the world."