Mayo Clinic study uncovers key differences among ALS patients

Mayo Clinic study uncovers key differences among ALS patients

By
Kevin Punsky

July 20, 2015

Mayo Clinic researchers conducted a statistical analysis to determine the degree of divergence in differentially expressed RNAs in patients with c9ALS (black) with those in patients with sALS (purple) or healthy individuals (green, controls). Changes in c9ALS distinctly diverge from the other two groups as the black circles are farthest from the purple and green circles. Each circle represents an individual included in the study, color-coded depending on its group membership, and shown in a linear transformation on a vector space (3-D cube).

JACKSONVILLE, Fla. — Researchers on Mayo Clinic’s Florida campus have identified key differences between patients with sporadic amyotrophic lateral sclerosis (ALS or Lou Gehrig’s disease) and those with the most common genetic form of ALS, a mutation in the C9orf72 gene.

Their findings, reported online today in Nature Neuroscience, demonstrate that ALS patients show abnormalities in levels and processing of ribonucleic acids (RNA), biological molecules that determine what gene information is used to guide protein synthesis.

More than 30,000 Americans live with ALS, a condition that destroys motor neuron cells that control essential muscle activity, such as speaking, walking, breathing and swallowing. While increasing efforts are geared toward therapeutic development, an effective drug for ALS has yet to be identified, in large part because of our incomplete understanding of the disease.

“Our results using advanced, modern laboratory techniques called next-generation sequencing, allowed us to acquire a library of new knowledge about patients with ALS,” says the study’s senior author, Leonard Petrucelli, Ph.D., chair of the Department of Neuroscience on Mayo Clinic’s Florida campus.

Dr. Petrucelli and Hu Li, Ph.D., assistant professor of pharmacology on Mayo Clinic’s campus in Rochester, Minn., led a team of investigators who carefully analyzed the RNA from human brain tissues. They found that ALS brains had numerous RNA defects, compared to nondisease brains. They also predicted molecular events that may be altered due to the changes found in RNAs involved in pathways regulating those events and that may contribute to ALS.

While the researchers observed some commonalities, they also found many distinctions between the RNAs that were altered in sporadic versus C9orf72 mutation-associated cases. This suggests there may be different factors contributing to ALS in patients. The success of future therapies may need specific tailoring to the specific root cause of a patient’s motor neuron disease. Furthermore, the large volume of data obtained from their study, which was deposited into a public genomics data repository, provides a wealth of information available to other researchers to accelerate ALS research.

Researchers used systems biology to generate networks that show the associations of differently processed RNAs in the cerebellum brain region of patients with c9ALS. The main pathway affected in this brain region is that of RNA processing. Cell signaling, synaptic function, and cellular trafficking pathways also were highly affected. Genes are represented in this image by nodes of different sizes and colors, which vary according to their connection degree. Edges are colored depending on their proximity and influence to other genes.

Key to the success of their study was procuring samples from individuals who generously donated their tissues for research purposes to the Mayo Clinic after their passing. Close collaborations among the Petrucelli laboratory, Kevin Boylan, M.D., director of the ALS Certified Center of Excellence on Mayo’s Florida campus, and Dennis Dickson, M.D., director of the neuropathology laboratory on the Florida campus, facilitated access to these precious samples.

“Last year, the ALS Ice Bucket Challenge raised a remarkable amount of money to support ALS patients and research,” Dr. Petrucelli says. “Without the extreme generosity of both monetary donors and patient tissue donors we could not make these strides in understanding this devastating disease.”

The Petrucelli laboratory is conducting follow-up studies based on the data from this study to determine which alterations are important in ALS pathogenesis. The researchers also will study which alterations should be developed as diagnostic and prognostic biomarkers or as therapeutic targets that may offer hope to patients with ALS.

This work was supported by the National Institutes of Health/National Institute on Aging (R01AG026251 and P50AG016574); the National Institutes of Health/National Institute of Neurological Disorders and Stroke (R21NS089979; R21NS084528, R01NS088689; R01NS077402; R01NS063964; P01NS084974); the National Institute of Environmental Health Sciences (R01ES20395); the Department of Defense (ALSRP AL130125); Mayo Clinic Foundation; Mayo Clinic Center for Individualized Medicine; ALS Association; Robert Packard Center for ALS Research at Johns Hopkins; Target ALS; Canadian Institutes of Health Research; Siragusa Foundation; Robert and Clarice Smith and Abigail Van Buren Alzheimer’s Disease Research Foundation; and Donors Cure Foundation.

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MEDIA CONTACT: Kevin Punsky, Mayo Clinic Public Affairs, 904-953-0746, punsky.kevin@mayo.edu