Scientists edit heart muscle gene in stem cells, may be …

Posted: July 25, 2018 at 6:42 pm

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In other words, the impact certain variants could have on your health remains a guessing game.

"Patients often ask us what do these variants of uncertain significance mean. But in reality, we don't know most of the time ourselves. So we end up having to follow the patients for the next five, 10, 20, or 30 years to see if the patient manifests the disease or not," Wu said.

"Here, we now have a way to shorten that time because we can generate patients' induced pluripotent stem cells from blood."

How do those stem cells then help predict if a variant is harmful or not? They can be differentiated into heart cells.

If the heart cells look abnormal, that probably means the variant of uncertain significance is pathogenic, meaning it's capable of causing disease.

If the heart cells look normal, that probably means the variant of uncertain significance is actually benign.

"This is one of the very first proof of principles to show that concept," Wu said.

'An important step towards precision medicine'

The researchers found 592 genetic variants across the 54 people. While 78% of the variants were categorized as benign, there were 17 people who each carried a variant categorized as "likely pathogenic." For four of those people, their variant was hypertrophic cardiomyopathy-related.

So the researchers then took that knowledge and used CRISPR to turn the patient's stem cells with this MYL3 genetic variant from being heterozygous, meaning they have one normal and one recessive form of the variant, to being homozygous, so that they have two recessive forms of the variant.

Specifically, the researchers took the one study participant's blood cells, turned them into induced pluripotent stem cells, and then used CRISPR to edit those cells in a petri dish. The researchers then differentiated the edited stem cells so they would become heart muscle cells, and performed a comprehensive analysis to evaluate the variant, determining exactly how harmful the variant was or whether it was benign.

In this case, the study participant's variant was predicted to be benign.

A risk with using CRISPR is that it could introduce some unintended changes, but no off-target mutations were detected in the gene-edited cells, the researchers reported in their study.

"Much work remains to further develop stepping stones between editing cells in a dish and genome editing therapeutics that can treat patients, but studies such as this one help identify variants that are promising targets for therapeutic editing," said David Liu, core institute member of the Broad Institute and professor of chemistry and chemical biology at Harvard University, who was not involved in the study.

This gene-editing approach was found to be feasible in this one patient, but more research is needed to determine whether similar results would emerge among more patients.

"While it's very elegant, the major limitation of this work is that it took years of expensive work by a team of very talented scientists to do this for just one patient," said Dr. Kiran Musunuru, an associate professor of cardiovascular medicine at the University of Pennsylvania's Perelman School of Medicine, who was not involved in the new study but has conducted separate research involving CRISPR.

"It's an important step towards precision medicine, but going forward we will need to scale this up and be able to do this for dozens, hundreds, or even thousands of patients at a time, in a matter of weeks and much more cheaply," he said.

Time and cost are also limitations of this approach, Wu said.

"Cost-wise, it takes us probably about $10,000 and time-wise about six months," he said. Those six months would involve making the induced pluripotent stem cells, using CRISPR to edit the cells and then analyzing the differentiated heart cells.

Wu added, "but keep in mind that six months is actually still much better than the current alternative that we have, which is to tell patients that we don't know what the variant means."

The alternative would be following a patient with a variant for years, with the worrisome chance of a disease possibly developing or not developing. In either scenario, the patient as well as family members could have anxiety and stress.

Is this the future of gene editing?

"This addresses a major unmet need in patient care by helping determine whether your specific mutation is something to worry about," said Lagor, who was not involved in the study but has conducted separate research on CRISPR.

Then once a mutation has been identified as disease-causing, "this is an ideal platform for testing potential new drugs or gene therapy approaches in a patient-specific manner. This is truly personalized medicine," he said.

"The first therapeutic application of this technology would be to correct rare genetic diseases of the heart itself, where the potential benefit far outweighs the risk to the patient. Some of this technology already exists today, and it is now a matter of demonstrating that this can be done safely and effectively," he said.

"However, present-day forms of CRISPR technology do not work well enough in the actual heart muscle in a living being to correct a mutation for a disease like cardiomyopathy," he said. "It's possible that some future generation of gene-editing technology might be able to do the job of treating disease in the heart muscle, years or more likely decades in the future."

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