Why sequence a whole genome?
The main aim of sequencing the first human genome - back in 2005 - was to make a genomic map, indicating which genes are responsible for certain characteristics and hereditary diseases. But, in the end, this link is not quite so straightforward. Because you need to examine the genomes of thousands of people to be able to deduce anything useful. At the moment, this kind of work is done mainly in research centers, where the sequencing of whole genomes is used as an important research tool.
But reading full genomes (of human cells, viruses and bacteria) is also of value for establishing diagnoses, as well as for selecting and monitoring treatments. Experts believe that DNA-sequencing can become one of the most important tools used by doctors and specialists in their work – just as a standard blood analysis is now. “You can start by looking for hereditary diseases – which is already done today for breast cancer (BRCA 1 and 2 genes) – but sequencing the genome is also of interest for other, non-hereditary cancers,” explains Liesbet Lagae, program director life science technologies at imec. “Trouble is, a tumor is often made up of different sorts of cells, which have each undergone different mutations. At the moment, we can only look at the ‘average’ genome of the tumor at one specific time. This is because ‘deep sequencing’ is still too expensive and time-consuming. But if we were able to sequence the genome of a cell, quickly and cheaply, we could monitor the various types of cancer cells very precisely over a specific period of time and so treat them better.”
“This sort of single-cell sequencing is important for deciding on the correct cancer treatment, such as with multiple myeloma,” adds Wilfried Verachtert, director ExaScience Life Lab. “With some cancers, doctors can see that the cell types in the tumor mutate during treatment. And if that happens, a new kind of treatment has to be started. But if we were able to screen the composition of the various tumor cells with greater frequency, it would make it much easier to treat these more complex cancers.”
Our blood not only contains our own hereditary material, but also that of viruses and bacteria. Detecting these genomes is of value for detecting and treating infectious diseases, such as Ebola or new strains of influenza.
Despite the enormous possibilities opened up by DNA-sequencing, it is still not used routinely in day-to-day hospital practice,. In fact there are very few FDA-approved diagnostic tests based on DNA-sequencing. Why is that? Because the process is still too expensive and cumbersome.