Squirrels: They seldom appear to have the sniffles as they scurry nimbly up tree trunks. Why all this health? Researchers recently published a report on their analysis of what makes animals thrive and humans not in some cases - that is, what causes mutations to be disease-causing in one genome, but benign in another.

These researchers, at Duke University School of Medicine and Brigham and Women's Hospital, Harvard Medical School, have identified a mechanism that may explain this.

Their research compared human disease-causing mutations with corresponding sequences of around 100 animal species."What we considered is that for many mutations, there must be a buffering mechanism - another mutation that protects the animal from the detrimental effects of the disease-causing mutation," said Nicholas Katsanis, Ph.D., director of the Center for Human Disease Modeling and professor cell biology and pediatrics at Duke, according to a release.

The researchers considered whether disease suppression results from one or two additional substitutions on the same gene, buffering the harmful effect of the mutation; or whether several small substitutions throughout the genome form a type of shield.

Their research tracked changes in protein sequence that moved in concert with the disease-causing mutation and were possible candidates for offering protection. It seemed that if a species lost the "traveler," it would have to eliminate the mutation or become extinct.

The scientists engineered mutant proteins that were defective, then added secondary sites and were able to restore protein function.

"In the end, it looks like you can shield mutations with a single change elsewhere in the same gene, creating a single champion." Katsanis added, according to a release.

All genome research remains complex, however, Katsanis noted in a release. "It used to be black-and-white: mutation, bad; no mutation, good. But it's far more complex. We are now beginning to be able to compute the effect of mutations in the context of the rest of the genome. There is no question that this will improve our ability to interpret human genomes and inform clinical practice."

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