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Posts tagged ‘Alzheimer’s disease biomarkers’

Drug development for neurodegenerative brain diseases such as Parkinson’s or dementia, of which Alzheimer’s is the most common form, needs to focus on patients early in the disease, not those where brain damage has already occurred.

Diagnosing and treating patients more effectively earlier will, even if you aren’t able to instigate a cure, offer the ability to modify the disease progression and slow or delay when brain damage occurs.  In the case of Alzheimer’s, once the amyloid plaques (tangles of misshapen proteins) have accumulated in nervous tissue, it has so far been impossible to untangle or remove them.

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Last year, I interviewed Dr Todd Sherer, (then the Chief Program Officer) and now the CEO of the Michael J. Fox Foundation, who told me that: “biomarkers are a real focus of the foundation.” Sherer went on to say that:

“Parkinson’s is a difficult disease to diagnose, there is no definitive diagnostic test, so it ends up a clinical diagnosis.  Getting a biomarker that could help better confirm the diagnosis would allow people to get the correct treatment earlier in their disease”

Which is why I was interested to see new research published earlier this week in the journal Archives of Neurology (online first, August 27, 2012), by Sara Hall and colleagues at Lund University, University of Gothenburg and Skåne University Hospital in Malmo, Sweden.

Hall and colleagues describe how a panel of five cerebrospinal fluid (CSF) biomarkers allowed the differential diagnosis of common dementia from Parkinsonian disorders:

  • Beta-amyloid 42
  • Total tau
  • Phosphorylated tau
  • Alpha-synuclein
  • Neurofilament light chain

Patients with early symptoms of neurodegenerative diseases can be hard to diagnose.  Misdiagnosis can occur, which means patients may not respond to treatment or they could be enrolled into a clinical trial, and end up skewing the results.

Ensuring that we have the right patients in clinical trials is important as we seek to alter disease progression.  In other words it’s important to see whether new drugs or treatments are impacting the disease course.  If you have a wrongly diagnosed patient in a trial, then the drug may show no effect, not because it’s not effective, but that patient’s disease is not responsive.

Multivariate analysis indicated that the panel of 5 CSF biomarkers could accurately differentiate Alzheimer’s disease (AD) from Parkinson disease with dementia (PDD), and dementia with Lewy bodies (DLB). The Neurofilament light chain biomarker alone could differentiate PD from atypical Parkinson disease, Hall and colleagues noted.

Whilst the panel was not able to distinguish all forms of dementia, in an accompanying editorial Richard J. Perrin MD, PhD from the University of Washington, stated that this research “represents a significant step forward.” Perrin concluded that:

“Implementation of CSF biomarker panels such as this one should improve the efficiency of clinical trials and accelerate the evaluation and discovery of new effective treatments for neurological diseases.”

Summary

Developing biomarkers that assist in the ability to diagnose Alzheimer’s, Parkinson and dementia patients correctly, and then be able to monitor their subsequent disease progression, should be a key focus of those biotechnology and pharmaceutical companies that want to do innovative and rational drug development.

References

ResearchBlogging.orgSara Hall, MD, Annika Ohrfelt, PhD, Radu Constantinescu, MD, Ulf Andreasson, PhD, Yulia Surova, MD, Fredrik Bostrom, MD, Christer Nilsson, MD, PhD, Hakan Widner, MD, PhD, Hilde Decraemer, Katarina Nagga, MD, PhD, Lennart Minthon, MD, PhD, Elisabet Londos, MD, PhD, Eugeen Vanmechelen, PhD, Bjorn Holmberg, MD, PhD, Henrik Zetterberg, MD, PhD, Kaj Blennow, MD, PhD, & Oskar Hansson, MD, PhD (2012). Accuracy of a Panel of 5 Cerebrospinal Fluid Biomarkers in the Differential Diagnosis of Patients With Dementia and/or Parkinsonian Disorders Arch Neurol. DOI: 10.1001/archneurol.2012.1654

Richard J. Perrin, MD, PhD (2012). Cerebrospinal Fluid Biomarkers for Clinical Trials Arch Neurol. (August 27 Online First) DOI: 10.1001/archneurol.2012.2353

Changes in brain structure, function and molecular processes occur several years before clinical symptoms of Alzheimer’s disease (AD) become apparent.

The big question then, is can you detect patients who are cognitively normal, but will go on to develop AD before they show symptoms, i.e. pre-symptomatic patients?  The answer is “Yes” according to results published in the April 19, 2011 issue of Neurology by Brad Dickerson and colleagues.

In this small study, the team of researchers from two centers (Massachusetts General Hospital and Rush University in Chicago) followed a small sample of cognitively normal (CN) subjects over time with magnetic resonance imaging (MRI) and then sought to identify what structural changes had taken place in those subjects who were initially cognitively normal, but went on to develop AD, on average 11.1 years later.

The researchers found that changes in brain cortical thickness were associated with AD:

AD-signature cortical thinning in CN-AD converters in both samples was remarkably similar, about 0.2 mm (p < 0.05)

They concluded that:

By focusing on cortical regions known to be affected in AD dementia, subtle but reliable atrophy is identifiable in asymptomatic individuals nearly a decade before dementia, making this measure a potentially important imaging biomarker of early neurodegeneration.

Some of the limitations of this research and questions that come to mind are:

  • Small sample size: only 8 individuals who developed AD and 25 in the cognitively normal control group.
  • Reproducibility: the 0.2mm difference seen is small and the extent to which other centers may be able to reproduce this measurement is uncertain
  • Accuracy of detection: in any screening tool the issue of false positives and negatives arises i.e. in a larger sample size will there be a margin for error that results in some people being included in the pre-symptomatic AD group, when they may be normal?  Also will the proposed measurement remain valid in a large population of patients with other disease symptoms and chronic illnesses?
  • Validity of biomarker: are the changes in cortical thickness causally linked to AD or just an incidental correlation i.e. is this a valid biomarker?

Brad Dickerson in the excellent Neurology podcast available with this publication clearly sees this currently as a research tool, especially given the requirement for considerable computer power to make these types of cortical measurements in the brain.  The podcast interview is well worth listening to.

The MRI biomarker proposed by Dickerson is therefore not something that is really applicable to screen the general population at the moment.

However, the promise from this and other biomarker research is that at some point in the not too distant future we will be able to detect those at risk of developing AD. Those patients could then be given neuroprotective drugs that may delay the onset of the clinical symptoms of AD such as memory loss and cognitive impairment.

Biomarkers that identify those at risk of developing AD will also be useful as inclusion and screening tools for clinical trials of drugs aimed at slowing disease progression in pre-symptomatic patients.

Alzheimer’s disease has been called “The challenge of the Second Century,” we still have a long way to go before this is overcome.

Story Source:  BBC Health

ResearchBlogging.orgDickerson, B., Stoub, T., Shah, R., Sperling, R., Killiany, R., Albert, M., Hyman, B., Blacker, D., & deToledo-Morrell, L. (2011). Alzheimer-signature MRI biomarker predicts AD dementia in cognitively normal adults Neurology, 76 (16), 1395-1402 DOI: 10.1212/WNL.0b013e3182166e96

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