Friday November 12 2010
It is unclear if the brain changes will lead to Alzheimer's
Scientists are developing a “30-second Alzheimer’s screening test” reported The Daily Telegraph. It said that such a test “could be available in as little as two years”.
This news was based on research that gave MRI scans to 428 healthy people in their forties to look for changes in the intensity of white matter lesions (the nerve fibres) in specific areas of the brain. The study found that these brain changes were each present in 0.4-20% of participants and that their presence in specific areas was linked to poorer performance in some cognitive tests. There were also differences in the way men and women were affected.
White matter changes have previously been associated with poorer performances on some cognitive tests in older individuals, and this research looked for a similar association in younger people. However, it is important to emphasise that this research has not developed a test for Alzheimer’s or dementia, as some newspapers have reported.
The population included in the study were healthy and their performance in cognitive tasks is likely to still be within the normal range.
Ultimately, it is not clear from this research if the observed changes in white matter intensity during middle age would actually lead to dementia or Alzheimer’s disease in later life.
Where did the story come from?
The study was carried out by researchers from the Australian National University and Brunel University, and funded by the Leverhulme trust and the British Academy. The study was published in the PLoS One, the peer-reviewed journal of the Public Library of Science.
The research was reported poorly by the newspapers, which all hailed it as a ‘30-minute test’ for Alzheimer’s disease. The study looked at the presence of lesions called ‘white matter hyperintensities’ (WMH) in middle-age participants but did not follow people over time to see whether the lesions were associated with any subsequent risk of dementia, including Alzheimer’s disease. The people included in this study showed variation in how well they performed on tests of cognition, but they were healthy individuals and performance was not below clinically normal levels.
Different reporting sources seemed to feature similar misconceptions about this research so it is not clear whether this was due to them all overextrapolating the research in a similar way or if the press release for this study inaccurately presented the research.
What kind of research was this?
This cross-sectional study looked at MRI scans of healthy people aged between 44 and 48 to see whether there was an association between WMH and cognitive function. WMH are lesions that appear bright white on some types of MRI scan. They occur within the white matter of the brain, which contains the axons (the long connecting part) of nerve cells.
This differs from the ‘grey matter’, which are regions where synapses between nerve cells are found. White matter hyperintensities may be caused by local inflammation in the brain and loss of particular types of cells that support nerve cell function. These changes may affect how well signals travel between different areas of the brain and may affect cognitive function dependant on the brain regions involved.
The researchers say that most research has looked at the association between white matter hyperintensities and cognitive function in older people, aged 60 years of over. However, they wanted to see whether these associations were also seen in younger individuals.
What did the research involve?
The study included participants from an ongoing study, the PATH Through life Project cohort, that has recruited participants from Canberra, Australia, and the surrounding area. A total of 428 participants underwent an MRI scan (232 women, 196 males). The participants were between 44 and 48 years of age, with an average age of 47.
The medical histories of the participants was collected: 2.3% had had cancer, 3.0% heart disease, 0.9% stroke, 2.1% diabetes, 4.4% thyroid problems and 15.7% head injury.
The researchers measured the participants’ reaction times taken to press one of two buttons when a light came on. They also gave the participants cognitive tasks such as repeating a list of three to six words backwards, recognising faces, and remembering items on a shopping list 20 minutes after being told the list. They were also given a ‘spot the word’ test, which comprised of 60 questions and required participants to indicate which of the two forms is a valid word.
What were the basic results?
The researchers found that on tasks of immediate and delayed recall, women performed better than men did, whereas men were better at doing the backward word order test.
There was no difference between the men and women in white matter hyperintensities.
The researchers found that where there were associations between WMH and cognitive performance. The white matter changes seen tended to be in the frontal and temporal lobes (areas at the front and side of the brain that have been associated with executive functioning, language and memory) rather than the parietal and occipital lobes (areas at the back of the brain associated with processing sensory information and vision).
The researchers then calculated the proportions of people who had WMH in each specific area:
- frontal cortex WMH were found in 7 to 12% of participants
- temporal cortex WMH in 0.4 to 1.5%
- parietal cortex WMH in 15 to 21%
- occipital cortex WMH in 0.4 to1.5%
Associations were found between WMH and cognitive function, especially if the WMH was on the left side of the brain.
They found that in women the presence of WMH in the frontal cortex was associated with their reaction times, while WMH in the temporal cortex (at the side of the brain) was associated with deficits in face recognition in men. These associations remained even after taking into account education and a range of health variables, including vascular risk factors.
How did the researchers interpret the results?
The researchers said the finding that WMH were associated with cognitive deficits ‘was not in itself unusual, and is consistent with findings elsewhere’. However, they say that it is notable that ‘this association was evident in a community-based sample of functioning persons in midlife (rather than the elderly)’.
They suggest ‘the deleterious effects of neurobiological disturbance may manifest at an earlier age than is suggested by the broader literature’.
This research has assessed white matter hyperintensities and cognitive performance in a younger population than previously studied, and has found associations between changes, in particular, brain areas and poorer performance, on some cognitive tasks.
It is important to emphasise that this research has not developed a test for Alzheimer’s, as the newspapers have reported, or indeed any type of dementia.
The population included in the study were healthy and the variations seen between individuals in performance on the cognitive tasks would likely still be within the normal range.
Ultimately, it is not clear from this research whether the observed changes in white matter hyperintensity within midlife affect the likelihood that people will go on to have a dementia. Research testing this theory would need to follow a cohort over time rather than taking a one-off measure, as was the case in this study.
Other limitations of this study included its use of a one-off measurement in a relatively small number of participants. The information given regarding the participants’ medical history was also limited, and 16% of the participants did not provide any information on the severity and time of any head injuries they had received.
Alzheimer’s is a disease based on characteristic features identified through brain scans and clinical examination, plus the exclusion of all other causes of dementia. The causes for Alzheimer’s disease are not firmly established and there remains no predictive test.