The field of genetic engineering passed a major milestone this August. According to an article published in Nature, scientists have successfully corrected a severe disease-causing gene mutation in healthy, viable human embryos for the first time.
Our genetic code is the fundamental properties of what makes up each and every one of us and what makes us an individual. Our genes are pieces of the code that order everything in the cell what to do and sometimes there are errors in the code that can cause problems and disease such as cancer, blindness, or cystic fibrosis. Inherited errors in the code from either parent have been the hardest to fix thus far.
Scientists announced in August that they had used CRISPR technology in human embryos to repair a mutation linked to hypertrophic cardiomyopathy, which can cause sudden death. This achievement has implications for a range of devastating genetic conditions.
CRISPR, or Clustered Regularly Interspaced Short Palindromic Repeats, which alludes to the structure of code, is a revolutionary technology used in many areas of science to edit the genetic code of an individual. Its interdisciplinary origins come from the pioneering biochemist Jennifer Doudna and her microbiology counterpart, Emmanuelle Charpentier. Interestingly however, the patent on the technology is hotly debated as Feng Zhang and his laboratories lay claim to CRISPR technologies as well.
Nonetheless, it was Doudna and Charpentier that examined the potential of the bacterial gene-enzyme duo, CRISPR-Cas9. In essence, CRISPR is a gene in bacteria that recognises a viral attack and tells the Cas9 protein to essentially snip out some of the viral DNA and record it in its own DNA, creating a sort of library of past disease to repel possible future attacks. It is this snipping ability that was of interest to the intrigued scientists.
Although a long way from clinical use, this research is monumental and may pave the way for the use of gene editing in protecting babies from a variety of hereditary conditions. However, there has been a lot of speculation that this feat of human genetic engineering may also lead to eugenic ‘designer baby’ traits such as higher intelligence, more creativity, or greater athleticism.
An ethical quandary often ensues when discussing the consequences of making inherited changes to human DNA. If this technology is allowed to flourish uninhibited, could it lead to a major disparity between those with means being able to mail order designer babies and those born with disabilities being devalued? Ok, I’ll hold off on the Charlie Brooker dystopia just for now, but with currently only being on the frontier of this novel technology, who’s to say what possibilities are out there.
The study, published in Nature, comes hot of the heels of an American National Academy of Sciences, Engineering and Medicine committee convened to advise guidelines for modifying embryos. While some scientists called for a complete blanket ban on research involving human embryos and the editing of their DNA, a restricted approach was welcomed with the committee endorsing only alterations to genes known to cause “serious diseases and disability” and only if in a situation with “no reasonable alternative.” These stringent and explicit guidelines make it very difficult for any genetic research to be performed in the US, leaving it to countries like China, South Korea, and Sweden.
In this study, scientists at the flagship Oregon Health and Science University, along with colleagues in California, China and South Korea, reported that they repaired a mutation that causes a common heart condition in dozens of embryos.
If these embryos with the repaired mutation could develop into babies they would be free of the disease and free from passing it on to any descendants. The key to this study was that the embryos made were disease-free in all of their cells, with previous efforts only applying the change in some cells. Of course, this research is still in its infancy and is nowhere near ready for clinical trials. However, if the technology can be proven to be safe and prevent other mutations, it has the potential of helping out couples that cannot have healthy children.
There are over 10,000 diseases caused by specific inherited traits including breast and ovarian cancers, cystic fibrosis, Tay Sach’s disease, and some early onset Alzheimer’s cases. Ireland has one of the highest per capita amount od cases of cystic fibrosis, caused by an error in the CFTR gene, and this technology could help couples who are carriers of the gene have healthy, CF-free babies.
Genetic screening to identify mutations in embryos is already common among couples undergoing in vitro fertilization. Another ethical issue arose surrounding prenatal screening in Iceland, with close to 100% of parents whose embryos tested positive for Down’s Syndrome choosing to abort.
In any case, fertility specialists one day may be able to offer the option to repair the DNA of an embryo instead of discarding it if a mutation is found. Right now the procedure is only experimental and the embryos that were used in the study published were destroyed after three days.
Outside of the ethics debate, the research did reveal one exciting new discovery on how embryos repair themselves. Usually, genes that copy a DNA template introduced by scientists carry out the editing process. In these embryos, the sperm cell’s mutant gene ignored that template and instead copied the healthy DNA sequence from the egg cell. The mutated gene in question is the MYBPC3 gene, which can cause hypertrophic cardiomyopathy, a disease affecting about 1 in 500 people. If one of the parents has an affected gene, there is a 1 in 2 chance of a child receiving it.
Sperm from an affected male fertilized twelve eggs from healthy women. After CRISPR-cas-9 was injected into the sperm, it acts as a scissors snipping out mutated sequence of DNA from the male gene.
The researchers injected a healthy template DNA sequence in the fertilized egg, hoping it would copy the template sequence into the cut section. Instead, the male gene copied the healthy sequence from the female sequence, which was surprising and interesting as we do not know and can only speculate why this happened. Perhaps it’s an evolutionary response to growth and development. It is currently thought that the same process should occur for disease-causing mutations on maternal genes by copying the healthy paternal genes. The technique would not work, however, if both paternal and maternal genes were mutated.
The new research although raising ethical concerns, has shown new insight into infertility and miscarriage, something that affects many people. Whichever side of the fence you lie, it’s clear to see that we are on the verge of something great.
Orla Daly – Science Editor
