More than 1 million women have had genetic testing of BRCA1 and BRCA2, genes in which mutations can dramatically increase the risk for early onset breast and ovarian cancer. But for many women the test results have been ambiguous. That’s because it’s not clear where certain genetic variations are harmless or cause cancer.
BRCA1 was amongst the first cancer predisposition genes discovered, and it has been studied for over 20 years. The gene produces a protein that repairs DNA damage, which might otherwise lead to the formation of tumors. Since its discovery, researchers and clinicians have identified many genetic variations in BRCA1, but for most of these, we are unable to tell whether they impair function of the gene – raising the risk of cancer – or whether they are perfectly harmless.
Our research team works in the emerging field of genomic medicine, which uses an individual’s genetic information to prescribe care. We recognized that such “variants of uncertain significance” limited the utility of genetic testing and the prospects for genomic medicine. We know that problem is likely to get worse, as the number of uncertain variants in BRCA1 and other “medically actionable” genes is expected to grow exponentially as genetic testing is expanded to entire populations.
In a study, we set out to apply CRISPR genome editing to solve the challenge posed by these variants of uncertain significance. CRISPR has tremendous potential because the technology allows researchers like us to tinker with human genes. CRISPR allows us to make very specific changes, “edits” to our DNA – thus the phrase, “genome editing.”
Although there are many studies that are attempting to use CRISPR to treat disease, it can also be used to introduce specific mutations into human cells that grow in a dish, for the purposes of studying what effects these mutations have on the cell – for instance, whether or not they cause a gene to malfunction.
In our study, we used CRISPR genome editing to deliberately engineer some 4,000 different variants of the BRCA1 gene in human cells, nearly all possible variants in the most important regions of this gene. Importantly, the survival of the human cells that we used is dependent on intact function of the BRCA1 gene. As a consequence, the cells containing mutations that disrupted the function of the BRCA1 gene were unable to survive. On the other hand, the cell containing mutations that had no effect on the function of the BRCA1 gene were just fine. Using DNA sequencing, we tracked which mutations were associated with cell death versus cell survival.
When we compared the mutations that caused cell death to variants that are known to increase cancer risk, we noticed that they were the same. This gave us the confidence to say that the behavior of these variants in the cells in the dish was predictive of cancer risk in humans.
Source: Gene-editing technique CRISPR identifies dangerous breast cancer mutations : The Conversation