mosaicism – BioQuakes

The Third International Summit on Human Genome Editing issued a closing statement a few weeks ago calling for a pause on human genome editing – not permanently as some activists had hoped on ethical grounds, but instead for the near future because the technology is not currently sufficiently advanced as to ensure success. Gene editing involves editing embryos outside the womb and then implanting them to establish pregnancy. In addition to the numerous ethical concerns, such as a pathway to eugenics that the technology might lead to, the summit decided that the risks are simply too great at the present time.

This is because the edits made can result in unintended – and sometimes dangerous – consequences for the embryo that traditional DNA screenings may not pick up on. Gene editing works by unraveling the double helix with helicase (just like in DNA replication), cutting the DNA strand with an enzyme, and then having the cell’s own mechanisms, such as primase and DNA polymerase, combined with the new “blueprint” for DNA, tell the cell the order the nucleotides are placed in and complete the double helix again to form a complete, but modified, DNA strand. However, sections of DNA can be permanently lost or mistranscribed in the process, resulting in genetic disorders or cell malfunction, including cancers. These are similar to the risks that occur during DNA replication and the general life of the cell, but are significantly more likely to occur. Furthermore, mosaicism, often seen on small levels like calico cats (where different cells receive different activated genes than others), can occur on a massive scale, where some cells receive edits and others don’t, leading to health problems down the road for the embryo, if it survives at all.

As a result, the summit, composed of the world’s leading experts in CRISPR technology and research, decided to enact a pause on human genome editing for now. As the technology advances and is made safer, however, they claim that they will reconsider it. Until then, the use of CRISPR is limited to other organisms, such as plants and lab animals.

Over and over again, we have been told that our personality traits, our idiosyncrasies, our weaknesses, and our merits are all because of our genome. Supposedly, if someone studies our DNA, they will know exactly the type of person we are, but is that really true? According to new research, it’s not. Researchers have discovered that is extremely common for a person to have mosaicism, or multiple genomes. In other words, chimeras make up a higher fraction of people than scientists originally thought. Some have many variations, or mutations, in certain parts of the body, and some people even have genomes that are from other people. People can acquire a different set of genes along with their original genes as early as in the womb. Previously, there were just hints about the idea of multiple genomes, but the hints have turned into definite statements. The evidence of multiple genomes is changing the way scientists think. Links between rare diseases and multiple genomes are becoming apparent. After figuring this out, scientists are figuring out links between more common disorders and genome multiplicity. Although many forms of cancer and other diseases are linked to mosaicism, most instances of multiple genomes are benign. It is also changing the way that forensic scientists view DNA evidence in crime investigations. The biggest change of all is perhaps that scientists now have to consider that DNA from a finger prick may not be the same DNA in a muscle cell or brain cell. This means that scientists can’t tell what is happening in all the organs just from a simple blood test or test from one organ. They can’t be certain of what is happening in other parts of the body. However, scientists are hard at work discovering more powerful ways to investigate our multiple genomes.

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BioQuakes

AP Biology class blog for discussing current research in Biology

Tag: mosaicism

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