Alzheimer’s ‘is not one disease’ and can be grouped into six distinct categories, researchers have claimed.
Scientists reviewed five existing medical studies which analysed more than 4,000 patients battling the memory-robbing disorder.
They discovered Alzheimer’s could be split into six different groups – depending on how badly patients were affected. And they all had genetic differences.
The 18-strong research team, from a host of prestigious universities, hope the findings will bring them one step closer towards an Alzheimer’s cure.
And they also claim the results could explain why the trials treating all patients with the same drugs often prove unsuccessful.
Attempts to stop the neurological disease in its tracks have so far failed as scientists remain unsure as to its exact cause.
Alzheimer’s – the most common form of dementia – affects around 5.5million people in the US and 500,000 in the UK, figures show.
The study involved researchers from Boston University, the Virginia Puget Sound Health Care System and Indiana University.
The project was led by Dr Shubhabrata Mukherjee, of the department of general internal medicine at the University of Washington, Seattle.
‘Alzheimer’s, like breast cancer, is not one disease,’ Dr Mukherjee said on the back of the findings.
‘I think a good drug might fail in a clinical trial because not all the subjects have the same kind of Alzheimer’s.’
‘This study is not the end, it’s a start,’ Dr Mukherjee added of the findings, published in the journal Molecular Psychiatry.
All of the participants had late-onset Alzheimer’s, the most common form of the disease – when someone is diagnosed at 65 or over.
After more than two years of attempts, the researchers managed to standardise the different studies’ cognitive test scores.
They all assessed the patients on four key factors – memory, language, ‘executive functioning’ and ‘visuospatial functioning’.
Executive functioning is the set of skills that enables a person to get things done, such as time management and paying attention to tasks.
Visuospatial functioning refers to the way a person relates visual information to the space around them. This is used when walking through a door to avoid bumping into the frame and when crossing the road to gauge the speed of a oncoming car.
The researchers then used the data to bracket the patients into six different types of Alzheimer’s.
Dr Mukherjee and colleagues found that 39 per cent of the patients scored poorly across all four factors.
The next largest group, which 27 per cent of the participants were in, included those whose memory scores were substantially worse than their other results.
In the smaller groups, 13 per cent of the participants had language scores that were significantly lower than their other ones, while 12 per cent scored worse in visuospatial functioning.
Just three per cent of the participants scored substantially worse on their executive functioning tests than on the other three factors.
Six per cent of patients were bracketed in the final group, which saw them score worse across two of the four factors.
The researchers then analysed the DNA of 2,431 of the participants to determine if genetic subgroups exist between the different types of Alzheimer’s.
They found 33 specific locations throughout the patients’ genetic make-up that influence what group of Alzheimer’s they fit into.
A variation of the APOE gene, which is very strongly associated with Alzheimer’s in Europeans, was found to be particularly linked to those with poor memories.
Although tests can identify whether a person carriers the APOE gene, the researchers stress not everyone with the gene develops Alzheimer’s and some become ill even without it.
Several years ago, the International Genomics of Alzheimer’s Project Consortium published the largest genetic study of Alzheimer’s.
They found around 20 DNA locations associated with the disease and classed it as just one disorder.
The researchers hope their study will help towards a cure, which world leaders are hoping to achieve by 2025 – but an effective treatment has not even been developed.
Study co-author Dr Paul Crane, from Washington University, said: ‘We have found substantial biological differences among cognitively defined subgroups of Alzheimer’s patients. The implications are exciting.’
Speaking of the study, Dr James Pickett, head of research at Alzheimer’s Society said: ‘We know that there is no “one size fits all” approach for people with Alzheimer’s disease – a treatment that might work for one person might not work for another.
‘This innovative research suggests that the symptoms people with Alzheimer’s experience might be linked to genes and builds on the idea of personalised medicine as the best approach for Alzheimer’s disease.
‘Our own researchers in Exeter and Edinburgh are looking into genes and how they’re linked to symptoms and disease progression to help transform dementia medicine into a tailor-made system of person-centred care.
‘Although this study involved over 4,000 people with Alzheimer’s, we would need further studies to confirm the results in other groups.’
Attempts to stop the memory-robbing disorder in its tracks have so far targeted the toxic build-up of the amyloid beta protein in the brains of patients. This gradually destroys neurons, causing memory loss and confusion.
However, last September, researchers at King’s College claimed that once these clumps have formed it is ‘too late for drugs’ to work.