Medellin, Colombia - When Gladys Betancur Piedrahita was a young girl growing up on a coffee farm in the Andes mountain town of Angostura in Colombia, her grandmother fell ill. Gladys watched her mother and aunt care for their mother before she died. Soon after, Gladys' aunt developed the same mysterious illness. She suffered for three years until, at the age of 38, she too passed away. Then, about a decade ago, Gladys' mother, Magnolia, started to exhibit the by now familiar symptoms.

At first, Magnolia repeated stories, telling them four or five times. She flung her food or buried it. She left the house and wandered around, lost. A soft-spoken woman, she turned, without warning, wildly aggressive.

Gladys, now 37, recognised the signs. Her mother, like other family members, had early-onset Alzheimer's disease.

Gladys' hometown is one of a handful in Colombia's rugged state of Antioquia where many residents - possibly because the area's remoteness has fostered generations of intermarriage - have a genetic mutation on a chromosome that causes early onset Alzheimer's. The result is that if one parent has the disease, their child has a 50 percent chance of developing it.

A scientific laboratory

In other parts of the world, no one can know if they will get Alzheimer's as no single gene has been identified as causing it. But the certainty of getting the disease if you carry the mutation has made this region a scientific laboratory of sorts, offering something no other place does - a possible answer as to how to prevent a disease that strikes millions around the world.

Medellin, the capital of Antioquia, is now home to a multi-million-dollar drug trial where researchers have enrolled residents to find a solution to early-onset Alzheimer's, in the hope of eventually being able to prevent the late in life form of the disease as well.

"We noticed there were families where generations of people have been sick," says Lucia Madrigal, 64, a nurse who, along with a neurologist, first began researching Alzheimer's in the area. "So we started studying them. Our question was, what happens to these people? What happened to them that so many generations of the same family were sick?"

Although men and women have the same chances of getting Alzheimer's, a disease known for the toll it exacts on caregivers, the burden of care in Colombia, like elsewhere in the world, typically falls on women - wives, mothers, daughters, aunts - who cope with caring for their families even as they know that their loved ones, and they themselves, face frightening odds.

As the research facility at the University of Antioquia races against time to find a preventive solution - they are in the fourth year of the clinical trial and have four more years to go - for most of these families, Alzheimer's is already a reality.

Caring from dawn until after dusk

Gladys never stops working. Her routine has calcified - a relentless march from dawn until after dusk, day in and day out. After she sends off her two daughters - one to work, the other to school - she settles into a daily care routine for Magnolia, now aged 59. Gladys fixes her breakfast, bathes her, then begins physiotherapy, which includes massaging her skin.

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"I take her out when the day is nice and then put her in bed to prepare lunch," she explains. Gladys then single-handedly lifts Magnolia into a chair to feed her, careful not to hurt her mother's spine in the process. "Physically, it's hard because she's very rigid."

In the afternoon, more therapy before Gladys prepares dinner, cleans the house and takes care of her pets (three cats and two dogs). She puts her mother to bed at 8:30pm. "Mentally, it makes me depressed, but you start getting used to it."

Gladys used to run a grocery store, but when her mother fell sick, she quickly realised that taking care of Magnolia would be a full-time job. Although Gladys has two sisters and a brother who could help, they had to keep their jobs to help out financially.

"One of us had to stop working, and I decided to be the one [to] do that," Gladys says. "It was not an obligation," she quickly adds. "It was my wish to do so."

She sold her store and now sells cosmetic products from a catalogue to neighbours and relatives from home.

Clinical trials

The last time Gladys took a day off was a year and a half ago. Her sisters volunteered to take Magnolia for the day.

"I relaxed and slept until late," she says. "I went out to the cinema, went for a hike and went out to eat with my daughter."

But when Magnolia was returned, she was sicker than usual. Gladys believes it was because of the change in temperature - she was in a windier neighbourhood - and she had to be taken to the hospital. The incident convinced Gladys that she should never let her mother out of her sight.

"The caregiver is often alone, dedicating 24 hours a day to the sick person," Lucia, the nurse, explains. "They have a strong physical and mental burden day after day."

The only time that Gladys is apart from her mother now is when she and her brother go to participate in the clinical trial, a trip she rushes through every 15 days.

"I have hope that the study will have results. I really dedicated myself to it," she says. "I don't want my daughters to go through this."

For either of her daughters to hold the gene, Gladys would have to have it. She doesn't know whether she does - none of the clinical trial participants are told if they do. But she doesn't allow herself to believe she may get Alzheimer's even though she and her siblings face a coin flip in odds.

Despite seeing the sickness ravage her mother every day, "you live with the disease and try not to think of the disease," she says. "It's worse knowing than not knowing."

Despite Alzheimer's, a household of women and laughter

When I visit in June, Gladys' younger daughter, Angie Lizeth Rojo Betancur, who is 16 years old, is due to give birth in a week - to a boy. Right now, "it's only women in this house," Gladys points out.

Gladys, who moved to Medellin when she married, separated from her husband three years ago. Her father, who sold their coffee farm in the country, also lives in the city but in another house.

Her father, she says, has never helped her mother, through care or cash. "He never even changed her diaper," Gladys says. "I brought her here three years ago, and he's come twice to see her."

He lives alone in the house. In contrast, Gladys' home, which sits on a steep slope, is filled with jokes, animals - and laughter. Magnolia, propped up in a wheelchair and wearing a hoodie in the living room, caresses one of the cats curled up on her lap.

Gladys bends to scratch Magnolia's nose. "I know when it itches," she says; Gladys recognises Magnolia's telltale gesture.

Angie, who sits at the dining table eating a chocolate biscuit with a glass of milk, recalls her grandmother as being affectionate. Her earliest memory of that changing was when Magnolia, already showing signs of Alzheimer's, spanked her when she was seven or eight years old. Angie was stunned by Magnolia's behaviour but said she felt better after going to workshops at the Alzheimer's research facility, which explained the disease's symptoms to her.

Angie, who is studying to be a chemical engineer, says she wouldn't be able to manage with the baby if it weren't for her family.

Behind her, Gladys folds and refolds Magnolia's limbs to keep them supple and props her head against a fluffy lime-green pillow.

When the carers get Alzheimer's

The Piedrahita family's story echoes others' in Antioquia. Consuela de las Mercedes Valencia Mora, 69, a warm, chatty grandmother with close-cropped hair, says she grew up in Angostura surrounded by cattle, sugar cane and the dread of seeing an unknown disease spread its tentacles to claim friends and neighbours.

"Everyone would say, 'Oh, this one is going to die of stupidity' because we didn't know what the disease was," she says.

Consuela, who has four sisters, says that one of her two sisters who died of Alzheimer's had 14 children, four of whom now have the disease, while six others have already died from it. She says the four remaining siblings are unlikely to get the disease since they're past the age - typically their 30s and 40s - when people start showing symptoms of this particular mutation.

"When they call me to say somebody died, I just say, 'Thank God, it's okay. It's a horrible disease'," she says. "This is worse than AIDS and cancer."

It's especially tough on caregivers, she adds. "In every family that I see, I ask: 'Who is taking care of this person?' It's always the wives and daughters, but those very people get sick themselves."

In Gladys' darkest, bleakest moments - seeing Alzheimer's sever the arms of her family tree - she taps into a wellspring of emotion to fortify her resolve. "The love for my children gives me a lot of strength and the love that my mum always gave us," she says. "If the sick person was my father, it would've been more difficult because he was never there for us."

In the living room, Magnolia faces the street from her wheelchair, sunlight pouring in through the door and windows. Gladys heats milk for tea. One of her dogs settles near her feet. "The female dog, she learned everything from the cat," Gladys notes with fondness. "So she licks herself and behaves like a cat."

Sruthi Gottipati reported on a fellowship from the International Reporting Project.