Alzheimer’s disease is largely seen as one of old age.

The most common form of memory-robbing dementia, Alzheimer’s affects nearly 7 million Americans, most of whom are over the age of 65.

In general, about one in 14 people develop the disease by age 65, and one in three are diagnosed by 85.

But the hundreds of thousands of Americans living with Down syndrome are ‘destined’ to be struck by the deadly condition, experts have warned.

Down syndrome is one of the most common intellectual disabilities in the US, affecting about 200,000 to 400,000 Americans. Individuals with Down syndrome have an extra copy of chromosome 21, leading to developmental and intellectual delays.

That extra chromosome contains a gene that produces amyloid precursor protein (APP), which causes extra amyloid beta protein to form plaques in the brain and cause Alzheimer’s disease.

As a result, half of adults with Down syndrome will be diagnosed with Alzheimer’s disease in their 40s, decades earlier than most patients. Nine in 10 will have it by age 59.

Experts speaking at the world’s largest dementia conference this week warned people with Down syndrome are at an ‘ultra-high risk’ of developing Alzheimer’s, and research on this population has been ‘largely neglected’ by scientists for decades.

About nine in 10 people with Down syndrome will be struck by Alzheimer’s disease

Doctors told the Daily Mail that despite ‘a generation of adults’ being left out of crucial research, it’s ‘an exciting time’ for the Down syndrome community, who are finally being enrolled in clinical trials.

Hampus Hillerstrom, president and CEO of Down syndrome research foundation LuMind IDSC, told the Daily Mail: ‘It’s a big deal, and the delay in including people with Down syndrome in clinical trials has been an issue in the past.’

Hillerstrom explained that while there were 18,000 participants in about 30 collective trials for the most recently approved Alzheimer’s medications, none of them included patients with Down syndrome.

He said: ‘So for 14, 15 years, there was no participation. And so a generation of adults were left out of this research.’ 

It’s unclear exactly what causes Alzheimer’s disease – researchers believe the protein amyloid beta, found in the brain’s gray matter, builds up and forms plaques, which attack brain cells and cause overall brain volume to shrink. 

Amyloid beta is also thought to form from APP, which people with Down syndrome have significantly more of than neurotypical people. This accelerates the growth of amyloid beta throughout the brain. 

A 2025 study found people with Down syndrome accumulate amyloid 40 percent faster than neurotypical people.

In general, about one in 14 people develop Alzheimer’s disease by age 65, and one in three are diagnosed by 85

Hillerstrom said: ‘There’s just more of it, and it accumulates faster. And when you have Down syndrome, the onset is 20 to 30 years earlier than in the general population.’

In the 1980s, Hillerstrom said people with Down syndrome weren’t living as long as they are today.

‘Now that you have an aging population, these are acute problems, and families are losing their loved one with Down syndrome at record speed. It’s about four, four and a half years from the moment you get diagnosed with dementia [until you’re] dying of dementia. It’s much shorter than in the general population.’ 

The average life expectancy of a person with Down syndrome is 60. 

Other issues like sleep apnea and epilepsy are also more common in people with Down syndrome. 

The increased risk of sleep apnea is likely due to people with Down syndrome having smaller upper airways and larger tongues, which can make their airways more narrow and prone to obstructions.

They also have differences in their brain structures and neurotransmitter function, increasing the risk of seizures. 

Hillerstrom described people with Down syndrome as having ‘Stage 0’ Alzheimer’s from the time they’re born. 

Dr Juan Fortea, director of the Memory Unit at Hospital de la Santa Creu i Sant Pau in Spain, said during a presentation at the Alzheimer’s Association International Conference (AAIC) in Toronto: ‘They are nonetheless destined to develop Alzheimer’s disease. Alzheimer’s is the main medical problem and the main cause of death in people with Down syndrome.

‘It’s a limiting factor for life expectancy.’

Dr Fortea also warned that if researchers don’t spend more time studying the relationship between the two conditions, ‘we will not close the 20-year gap we have with the general population.’

He noted that while science on Alzheimer’s disease in the Down syndrome community has been ‘largely neglected,’ enrolling these patients in clinical trials would help turn the tide. 

For the first time, three trials are underway in the US looking at potential Alzheimer’s treatments specifically in adults with Down syndrome. 

Hillerstrom said: ‘Now there’s a very exciting time happening.’

The HERO Study, which is in stage one, involves a medication called ION269 administered once via lumbar puncture, which is when a needle is inserted into the spinal canal in the back. The goal is to make the brain produce less amyloid.

The ABATE trial, meanwhile, is testing an immunotherapy that may remove amyloid plaques in the brain. And ALADDIN is a clinical trial testing the effects of donanemab, which was approved by the FDA last year for the general population with early Alzheimer’s disease. 

All of the trials are actively enrolling people with Down syndrome who don’t yet have symptoms of Alzheimer’s.

Hillerstrom said: ‘There is a lot of evidence that if you wait until you have symptoms, it might be too late, and so you have to [start] at the prevention stage before you’re symptomatic. 

‘That’s the best time to intervene and have an impact.’

Hillerstrom is urging people with Down syndrome and their caregivers to sign up for clinical trials before symptoms of Alzheimer’s set in, as it could be only four to five years before they succumb to the disease. 

He told the Daily Mail: ‘If you wait until you have symptoms, it may be too late to help.

‘Anything you can do to participate in these treatment trials early, that’s the best thing you possibly could do for your loved one.’