There is currently no cure for dementia. Current treatments only address the symptoms of dementia, but do not target the underlying causes in the brain. In people who take available therapies, brain degeneration continues to progress at the same rate, but treatments can improve cognitive skills in the earlier stages, for a limited period of time.
However, therapies that target the biological causes of some forms of dementia are currently being trialled. There is some emerging evidence from recent trials showing that such therapies targeting the underlying pathology in the brain may be able to slow the progression of dementia – in particular with Alzheimer’s disease. There is also speculation from some researchers that it may be possible to halt the progression of Alzheimer’s in the future – however there is currently no supporting evidence of this. Any possible cure is likely to be limited to the earlier stages of dementia, preventing further decline. If these therapies do become available, it will become important to diagnose people in the earlier stages, before extensive brain degeneration has occurred. It is important to note that loss of brain cells – as a consequence of dementia – is an irreversible process and is not considered curable.
The only way to slow or even potentially halt the progression of dementia is to target the underlying pathological processes. Only by studying these potential treatments on large numbers of people we will come to learn which treatment strategies are likely to succeed.
For many years, researchers have searched for therapies that could slow or halt the progression of Alzheimer’s disease. Over 200 drugs have reached early stage clinical trials since 2003, when the last drugs for Alzheimer’s were listed. However, none of these potential therapies have been successful enough for approval and retail. There is cautious optimism amongst many researchers that we may see therapies that target the underlying pathology in Alzheimer’s disease in the near- to medium-term future. Examples include therapies based on antibodies and ultrasound.
Another important point to note is that dementia refers to a class of diseases that includes Alzheimer’s disease, vascular dementia, Lewy body dementia, frontotemporal dementia, and others. Each of these diseases have their own unique pathological hallmarks in the brain. Hence it is likely that future treatments will be specific to each disease. Therefore, large numbers of people with different types of dementia will be needed for research, as treatments will likely differ.
Institutions and organisations which trial therapies typically aim to recruit people in the earliest stages of dementia, and even in the prodromal stage – where signs of disease are present, but not sufficient to reach the classic diagnosis. Volunteers for these studies may receive a variety of treatment deliveries such as tablets, intravenous injections or ultrasound.
One day we may be able to accurately and routinely diagnose the very early stages of Alzheimer’s disease, and then apply interventions and treatments to prevent or dramatically slow disease progression. If this future is indeed possible, it will only be realised through continued basic research and large clinical trials with human participants. Treatments cannot be approved until they have been extensively trialled in people. In addition, an important factor limiting the speed of translating basic findings into clinical use is the difficulties and costs associated with recruiting large numbers of people with dementia.
The antibody aducanumab reduces Aβ plaques in Alzheimer’s disease (Nature; Sevigny et al., 2016)
A clinical trial is being undertaken in the USA, administering antibodies against Beta-amyloid. Beta-amyloid is a protein which aggregates to form plaques in the brains of people with Alzheimer’s. Beta-amyloid plaques are one of the hallmarks of the disease, and are considered to be a major cause of the loss of brain cells and cognitive decline seen in Alzheimer’s.
165 volunteers were recruited to this study. Eligibility criteria included age between 50 – 90, having either prodromal* or mild Alzheimer’s disease, a positive PET scan for the presence of amyloid, and no evidence of other possible causes of dementia. Researchers conducted interviews with participants in order to assess their baseline cognitive abilities and daily functioning and performed baseline PET scans to measure amyloid levels in the brain.
Volunteers received intravenous injections of either the antibody aducanumab or placebo (saline) every 4 weeks for one year. 125 participants completed the one-year treatment. Researchers found that people who received the higher doses of aducanumab had lower levels of amyloid at 12-month follow-up in comparison to when they started the trial. Researchers also found that participants receiving the highest dose had a slower rate of decline in both cognitive function and daily functioning compared to people receiving the placebo. Interestingly, people who had a very strong reduction in beta-amyloid levels did not experience significant decline in cognitive scores 1 year after beginning treatment. This is unusual for Alzheimer’s disease, as it is a progressive dementia.
This research is an important step towards finding a cure for Alzheimer’s disease, as it demonstrates that antibodies against amyloid can enter the human brain, reduce amyloid levels, and apparently slow cognitive decline. The research also supports the hypothesis that levels of amyloid are a major contributing factor to the progression of Alzheimer’s disease. There are several antibodies currently being examined for therapeutic value.
*Prodromal refers to people with deteriorating cognitive function, but below the threshold for Alzheimer’s diagnosis, and with a positive biomarker for amyloid.