An experimental drug may prevent early-onset Alzheimer's in people genetically destined to get it, a study suggests. 

One in 100 people with the disease develop it in middle-age because they inherited faulty genes from their parents, known as Dominantly Inherited Alzheimer Disease (DIAD).

The gene leaves them with a nearly 100 percent chance of developing Alzheimer's, the most common form of dementia, in their 30s, 40s, and 50s, making them destined to die from the disease by the time they reach their 60s.  

Now, researchers in Missouri are testing a drug that prevented half of these patients from suffering the memory-robbing disorder.

They used gantenerumab, a drug that works by attacking toxic proteins called amyloid in the brain.

Gantenerumab is no longer in development due to mixed results in earlier studies, but the team believes their study proves that clearing amyloid is the key to beating the disease.

And the team says their findings have broader implications. They believe new drugs with similar mechanisms could prevent Alzheimer's for millions more.

People with the faulty gene, gene presenilin 2 (PSEN2), have a nearly 100 percent chance of developing Alzheimer's, making the findings 'exciting,' the researchers said.

The team also suggests the drug could lead to potential Alzheimer's treatments for all of the 7million Americans with the memory-robbing disease.  

Dr Randall J Bateman, senior study author and DIAN director at WashU Medicine, said: 'I am highly optimistic now, as this could be the first clinical evidence of what will become preventions for people at risk for Alzheimer’s disease. 

'One day soon, we may be delaying the onset of Alzheimer’s disease for millions.'

Alzheimer's disease is the most common form of dementia, a group of neurological disorders that impact memory, language, problem-solving, and other cognitive abilities.  

According to the Alzheimer's Association, an estimated 6.7 million Americans are living with Alzheimer's disease in 2023. This number is expected to double by 2060. 

DIAD accounts for one percent of cases, the Wash U researchers estimate.

Alzheimer's disease is linked to a build up of toxic proteins beta amyloid and tau, which accumulate in the brain and form plaques that disrupt neurons and kill brain cells. 

People with a PSEN2 gene develop excess levels of these proteins, almost always resulting in Alzheimer's. 

However, it's still unclear if Alzheimer's causes the build-up or the build-up causes the symptoms of Alzheimer's. 

Published in The Lancet Neurology, the new study looked at 73 adults who inherited the faulty gene.

All participants had either no or very mild cognitive decline - a precursor to dementia - and were between 15 years before and 10 years after their expected age of Alzheimer's onset, based on family history.

Each person in the study received gantenerumab, a monoclonal antibody drug in development by Hoffmann-La Roche. 

Monoclonal antibody drugs are meant to mimic the body's natural disease-fighting antibodies and trigger the immune system to attack foreign invaders like amyloid. 

The researchers compared participants who received gantenerumab to placebo participants in their earlier trial. 

Gantenerumab had received mixed results in the past in patients with early symptomatic Alzheimer's. 

For example, participants who took the drug for two to three years and then received another drug or a placebo in the earlier trial had no changes in cognitive function. 

This led to Hoffmann-La Roche discontinuing development in 2023.

However, the new study found those on the drug for an average of eight years and who did not have symptoms halved their risk, suggesting treatment may be necessary in these high-risk patients several years before symptoms appear.

Though the study was limited to people with genetic forms of Alzheimer's, the authors believe the results could lead to prevention and treatment efforts for all patients. 

This is because both early-onset and late-onset Alzheimer’s disease start with amyloid slowly collecting in the brain about two decades before symptoms begin. 

The researchers said though gantenerumab is no longer being developed, similar anti-amyloid drugs are being evaluated as preventive medications. 

Dr Bateman said: 'Everyone in this study was destined to develop Alzheimer’s disease and some of them haven’t yet.

'We don’t yet know how long they will remain symptom-free – maybe a few years or maybe decades. 

'In order to give them the best opportunity to stay cognitively normal, we have continued treatment with another anti-amyloid antibody in hopes they will never develop symptoms at all. 

'What we do know is that it’s possible at least to delay the onset of the symptoms of Alzheimer’s disease and give people more years of healthy life.'