Is it Alzheimer's disease or another dementia? Marker may give more accurate diagnosis

ScienceDaily (Nov. 30, 2011) — New research finds a marker used to detect plaque in the brain may help doctors make a more accurate diagnosis between two common types of dementia -- Alzheimer's disease and frontotemporal lobar degeneration (FTLD). The study is published in the November 30, 2011, online issue of Neurology®, the medical journal of the American Academy of Neurology.

"These two types of dementia share similar symptoms, so telling the two apart while a person is living is a real challenge, but important so doctors can determine the best form of treatment," said study author Gil D. Rabinovici, MD, of the University of California San Francisco Memory and Aging Center and a member of the American Academy of Neurology.

For the study, 107 people with early onset Alzheimer's disease or FTLD underwent a brain PET scan using a PIB marker, which detects amyloid or plaque in the brain that is the hallmark of Alzheimer's disease but not related to FTLD. The participants underwent another PET scan using a FDG marker, which detects changes in the brain's metabolism and is currently used to help differentiate between the two types of dementia.

The study found the PIB PET scan performed at least as well as the FDG PET scan in differentiating between Alzheimer's disease and FTLD, but had higher sensitivity and better accuracy and precision with its qualitative readings. The study found PIB had a sensitivity of 89.5 percent compared to 77.5 percent for FDG.

"While widespread use of PIB PET scans isn't available at this time, similar amyloid markers are being developed for clinical use, and these findings support a role for amyloid imaging in correctly diagnosing Alzheimer's disease versus FTLD," said Rabinovici.

The study was conducted at the University of California (UC) San Francisco, UC Berkeley and Lawrence Berkeley National Laboratory, and supported by the National Institute on Aging, the California Department of Health Services, the Alzheimer's Association, John Douglas French Alzheimer's Foundation and the Consortium for Frontotemporal Dementia Research.

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Yeast model connects Alzheimer's disease risk and amyloid beta toxicity

ScienceDaily (Oct. 27, 2011) — In a development that sheds new light on the pathology of Alzheimer's disease (AD), a team of Whitehead Institute scientists has identified connections between genetic risk factors for the disease and the effects of a peptide toxic to nerve cells in the brains of AD patients.

The scientists, working in and in collaboration with the lab of Whitehead Member Susan Lindquist, established these previously unknown links in an unexpected way. They used a very simple cell type -- yeast cells -- to investigate the harmful effects of amyloid beta (Aß), a peptide whose accumulation in amyloid plaques is a hallmark of AD. This new yeast model of Aß toxicity, which they further validated in the worm C. elegans and in rat neurons, enables researchers to identify and test potential genetic modifiers of this toxicity.

"As we tackle other diseases and extend our lifetimes, Alzheimer's and related diseases will be the most devastating personal challenge for our families and one the most crushing burdens on our economy," says Lindquist, who is also a professor of biology at Massachusetts Institute of Technology and an investigator of the Howard Hughes Medical Institute. "We have to try new approaches and find out-of the-box solutions."

In a multi-step process, reported in the journal Science, the researchers were able to introduce the form of Aß most closely associated with AD into yeast in a manner that mimics its presence in human cells. The resulting toxicity in yeast reflects aspects of the mechanism by which this protein damages neurons. This became clear when a screen of the yeast genome for genes that affect Aß toxicity identified a dozen genes that have clear human homologs, including several that have previously been linked to AD risk by genome-wide association studies (GWAS) but with no known mechanistic connection.

With these genetic candidates in hand, the team set out to answer two key questions: Would the genes identified in yeast actually affect Aß toxicity in neurons? And if so, how?

To address the first issue, in a collaboration with Guy Caldwell's lab at the University of Alabama, researchers created lines of C. elegans worms expressing the toxic form of Aß specifically in a subset of neurons particularly vulnerable in AD. This resulted in an age-dependent loss of these neurons. Introducing the genes identified in the yeast that suppressed Aß toxicity into the worms counteracted this toxicity. One of these modifiers is the homolog of PICALM, one of the most highly validated human AD risk factors. To address whether PICALM could also suppress Aß toxicity in mammalian neurons, the group exposed cultured rat neurons to toxic Aß species. Expressing PICALM in these neurons increased their survival.

The question of how these AD risk genes were actually impacting Aß toxicity in neurons remained. The researchers had noted that many of the genes were associated with a key cellular protein-trafficking process known as endocytosis. This is the pathway that nerve cells use to move around the vital signaling molecules with which they connect circuits in the brain. They theorized that perhaps Aß was doing its damage by disrupting this process. Returning to yeast, they discovered that, in fact, the trafficking of signaling molecules in yeast was adversely affected by Aß. Here again, introducing genes identified as suppressors of Aß toxicity helped restore proper functioning.

Much remains to be learned, but the work provides a new and promising avenue to explore the mechanisms of genes identified in studies of disease susceptibility.

"We now have the sequencing power to detect all these important disease risk alleles, but that doesn't tell us what they're actually doing, how they lead to disease," says Sebastian Treusch, a former graduate student in the Lindquist lab and now a postdoctoral research associate at Princeton University.

Jessica Goodman, a postdoctoral fellow in the Lindquist lab, says the yeast model provides a link between genetic data and efforts to understand AD from the biochemical and neurological perspectives.

"Our yeast model bridges the gap between these two fields," Goodman adds. "It enables us to figure out the mechanisms of these risk factors which were previously unknown."

Members of the Lindquist lab intend to fully exploit the yeast model, using it to identify novel AD risk genes, perhaps in a first step to determining if identified genes have mutations in AD patient samples. The work will undoubtedly take the lab into uncharted territory.

Notes staff scientist Kent Matlack: "We know that Aß is toxic, and so far, the majority of efforts in the area of Aß have been focused on ways to prevent it from forming in the first place. But we need to look at everything, including ways to reduce or prevent its toxicity. That's the focus of the model. Any genes that we find that we can connect to humans will go into an area of research that has been less explored so far."

This work was supported by an HHMI Collaborative Innovation Award, an NRSA fellowship, the Cure Alzheimer's Fund, the National Institutes of Health, the Kempe foundation, and Alzheimerfonden.

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The above story is reprinted from materials provided by Whitehead Institute for Biomedical Research. The original article was written by Matt Fearer.

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Sebastian Treusch, Shusei Hamamichi, Jessica L. Goodman, Kent E. S. Matlack, Chee Yeun Chung, Valeriya Baru, Joshua M. Shulman, Antonio Parrado, Brooke J. Bevis, Julie S. Valastyan, Haesun Han, Malin Lindhagen-Persson, Eric M. Reiman, Denis A. Evans, David A. Bennett, Anders Olofsson, Philip L. Dejager, Rudolph E. Tanzi, Kim A. Caldwell, Guy A. Caldwell, Susan Lindquist. Functional Links Between Aß Toxicity, Endocytic Trafficking, and Alzheimer’s Disease Risk Factors in Yeast. Science, 2011; DOI: 10.1126/science.1213210

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Step toward unraveling Alzheimer's disease

ScienceDaily (Oct. 27, 2011) — Scientists outline new methods for better understanding links between specific proteins and the risks associated with Alzheimer's disease in an article co-authored by University of Alabama researchers and publishing in Science Express.

In experiments using a series of model organisms, including yeast, microscopic roundworms and rats, the researchers show how basic mechanisms inside cells are disrupted when a specific human protein, known as the amyloid beta peptide, fails to properly fold. This study also shows the role a second protein, referred to by the scientists as PICALM, can play in modifying the problem.

"By using these yeast models, in combination with worms, we really are hopeful of finding a way by which we can understand and maybe combat Alzheimer's disease more rapidly," said Dr. Guy Caldwell, professor of biological sciences at The University of Alabama and one of three UA-authors on the Science article.

The research involved scientists from several universities and research institutes, including the Whitehead Institute and Massachusetts Institute of Technology, where the lead author, Dr. Sebastian Treusch, is affiliated. Treusch works in the lab of Dr. Susan Lindquist, a renowned expert in cell biology and collaborator with Caldwell on a grant from the Howard Hughes Medical Institute that funded part of this research.

While the repeated misfoldings of amyloid beta peptides within the human brain were previously known to trigger the death of neurons, resulting in Alzheimer's, Caldwell says the underlying mechanisms of toxicity weren't as well understood.

Properly functioning cells must efficiently deliver proteins and chemicals to other parts of the cell, Caldwell said. This research shows how the amyloid beta peptide interrupts a specific cellular pathway called endocytosis, preventing the delivery of other needed proteins to other parts of the cell.

"Understanding what is going wrong inside a cell, or what pathways or proteins might be directly linked to the mechanisms that are involved in Alzheimer's, is really a much more fruitful strategy for drug development."

Information drawn from the brains of deceased Alzheimer's patients, who previously donated their bodies to science, was also significant in the effort, Caldwell said.

Rapid advances in DNA sequencing methods and human genetic population studies are generating an overwhelming number of leads for researchers; those genetic studies, taken in combination with advantageous attributes of simple organisms, can reveal basic functions of genes and proteins and can be an insightful combination, Caldwell says.

"What this paper shows is that simple systems, like yeast and worms, can be engineered to discern mechanisms that might be associated with complex human diseases, and, by that, we may accelerate the path of discovery for advancing therapeutics for those diseases."

UA's lead author is Dr. Shusei Hamamichi, a former post-doctoral researcher in the Caldwell lab who earned his doctorate at UA while working alongside Caldwell and Dr. Kim Caldwell, also a co-author of the paper and an associate professor of biological sciences at UA.

In the paper's conclusion, the researchers describe the potential significance of the development in light of the challenges faced in understanding and treating Alzheimer's disease.

"The treatments available for AD are few and their efficacy limited," the scientists wrote. "Determining how best to rescue neuronal function in the context of the whole brain is a problem of staggering proportions."

"On a personal level," Caldwell said, "so many of us have been affected by family or loved ones who have suffered from Alzheimer's. It's a great privilege for us to be able to contribute to the respective avenues of our understanding of the disease. It's a devastating disorder. The societal cost of Alzheimer's disease is tremendous."

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The above story is reprinted from materials provided by University of Alabama in Tuscaloosa.

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Journal Reference:

Sebastian Treusch, Shusei Hamamichi, Jessica L. Goodman, Kent E. S. Matlack, Chee Yeun Chung, Valeriya Baru, Joshua M. Shulman, Antonio Parrado, Brooke J. Bevis, Julie S. Valastyan, Haesun Han, Malin Lindhagen-Persson, Eric M. Reiman, Denis A. Evans, David A. Bennett, Anders Olofsson, Philip L. Dejager, Rudolph E. Tanzi, Kim A. Caldwell, Guy A. Caldwell, Susan Lindquist. Functional Links Between Aß Toxicity, Endocytic Trafficking, and Alzheimer’s Disease Risk Factors in Yeast. Science, 2011; DOI: 10.1126/science.1213210

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Disclaimer: This article is not intended to provide medical advice, diagnosis or treatment. Views expressed here do not necessarily reflect those of ScienceDaily or its staff.

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