A new system for editing genes was believed to be the new cure for cancer and all inherited diseases. However, scientists have now discovered there could be dangerous side effects with this method. It could lead to unintended gene mutations.
The Crispr-Cas9 gene-editing technique is already being trialled in humans in China and further human trials are due to start the US next year. It allows geneticists to edit part of the genome by removing, adding or changing parts of DNA sequences. An enzyme, called Cas9 is used to cut a part of the genome in a specific location. Once this cut has been made strands of DNA can be added or removed. The enzyme is “guided” to the correct part of the genome by another molecule called “guide RNA“.
Earlier in the year, Dr Edze Westra predicted that this new technique could “cure all inherited diseases, to cure cancers, to restore sight to people by transplanting genes“. This came about after researchers used Crispr-Cas9 to restore sight to blind mice, as reported in Nature Methods.
So what is the worry?
Using this new method the blind mice were able to see again. However, scientists then reviewed the whole genome of these mice, rather than just the section they had changed. When they did this, they found two of the mice had other unexpected changes to their DNA. Over 1,500 small gene mutations, along with over 100 larger deletions and insertions were discovered. Although these mice seemed to have suffered no ill effects, small mutations can cause serious problems. For example, Cystic Fibrosis can be caused by a small deletion. This disease has devastating effects for those who are unlucky enough to have this small genetic change.
Scientists currently use a computer algorithm to predict changes in parts of the DNA which were not targeted by Crispr. Usually, these algorithms are very good, but they are not 100% failsafe. The algorithm was run in the trial with the mice, but none of the changes found were predicted by the algorithm.
Researchers are being advised to review the whole genome of test subjects when using Crispr system and to not rely on the computer algorithm alone. As with all new medical treatments, there are always potential side effects in the beginning. Research continues to try and improve this technique, so for now that cancer cure will have to wait.
Trusted Medicine Education: DNA and the genome explained
DNA is made up of four different chemicals, or “bases” which pair together. These bases are called Adenine, Guanine, Cytosine and Thymine, also known simply as A,G,C and T. They always pair in the same way, A with T and G with C. This pairing forms the DNA double helix shape.
Each section of DNA is known as a gene. Genes can vary in length from a few hundred base pairs to more than 2 million base pairs.
The genome is an organism’s complete set of DNA including all the genes. The human genome project is a project which aimed to work out the order of all the base pairs in human DNA. It estimated that there are between 20,000 and 25,000 genes, or 3 billion base pairs in the human genome. It is thanks to this project that advances in DNA sequencing and gene editing, as used by the Crispr technique, have evolved.
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Any opinions above are the author’s alone and may not represent those of his/her affiliations. Any comment is based on the best available evidence at the time of writing. All data is based on externally validated studies unless expressed otherwise. Novel data is representative of the sample surveyed. An online recommendation is no substitute for seeing your own doctor and should not be taken as medical advice. Article edited for publication by Dr Hannah Arnstein
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