Published: Fri, August 04, 2017
Health Care | By Jan Bell

Scientists edit human embryo to erase heritable heart condition

Scientists edit human embryo to erase heritable heart condition

For now, the scientists had removed a mutated gene from a human embryo, which, they said can cause heart attack.

Shoukhrat Mitalipov and his colleagues from Oregon Health and Science University have successfully used the CRISPR Cas9 gene editing technology to wipe out a genetically inherited heart mutation in embryos.

The new method uses the gene-editing tool CRISPR to target a mutation in nuclear DNA that causes hypertrophic cardiomyopathy, a common genetic heart disease condition which can cause sudden cardiac death and heart failure.

With advances in stem cell technologies and gene editing, researchers are finally starting to address disease-causing mutations that impact potentially millions of people. Pre-implantation genetic diagnosis allows the screening of embryos that are at risk of devastating single-gene disorders in the context of IVF and that eliminates vast amounts of human misery.

The technique would need to approach 100% effectiveness to be ready for clinical trials aimed at producing pregnancies, Mitalipov said.

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Safety is a key question because gene editing isn't always precise enough; there's the possibility of accidentally cutting DNA that's similar to the real target.

Research using human embryos is highly regulated, and is different between countries.

Critics of the study were quick to allege that the research team - whose work can not be taken much further in the United States given legal limitations - had already pushed the boundaries too far.

Taking sperm from a male donor who has hypertrophic cardiomyopathy, and an egg from a healthy woman, the team injected the CRISPR technology at the point of fertilisation to carry out the genetic repairs. Though it's still in the testing phase, CRISPR has been likened to eugenics or playing God by allowing scientists to create "designer babies" or wipe out diseases through the kind of genetic engineering now limited to plants and lower animals. It wasn't a flawless success-the rate of fixed embryos moved from the naturally expected 50% to 74%. The research team cleverly side-stepped mosaicism by using CRISPR at the same time as fertilising the egg, before its cells had begun dividing.

CRISPR, which was introduced in 2012, precisely cuts DNA but does not fix it. The first, done in China in 2015, involved embryos with serious genetic defects that prevented them from being brought to term. "Moreover, if such embryos were to grow up, as will doubtless occur in the future, there are likely to be unintended effects from modifying their genes", Fr. Pacholczyk continued.

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Scientists contacted by KPBS saw these results as a small yet successful step toward the development of new strategies for fighting genetic diseases in future generations.

Unlike past experiments that attempted CRISPR days after embryos had developed, this one did it at the time of fertilization.

Embryos' self-healing DNA came as a surprise, because gene editing in other types of cells usually requires an external template, Mitalipov says.

"What it does is, it searches out the one error in the 3 billion letters of the DNA code and it chops it out, and the DNA corrects itself", CBS News medical contributor Dr. David Agus explained on "CBS This Morning".

Agus also noted that in the experiments, the technique proved to be very precise in targeting the defective gene, leaving the rest of the embryo's DNA "untouched". The work is also consistent with recommendations issued in February 2017 by the National Academy of Sciences and the National Academy of Medicine joint panel on human genome editing. The United States forbids the use of federal funds for embryo research, and the Food and Drug Administration is prohibited from considering any clinical trials involving genetic modifications that can be inherited. But the finding could be good news for those concerned about designer babies, because embryos may reject attempts to add new traits.

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