[Genome sequencing and personalized medicine: perspectives and limitations]

DNA sequencing technologies have advanced at an exponential rate in recent years: the first human genome was sequenced in 2001 after many years of effort by dozens of international laboratories at a cost of tens of millions of dollars, while in 2013 a genome can be sequenced within 24 hours for a few hundred dollars (exome sequencing takes only a few hours). More and more hospital laboratories are acquiring new high-throughput sequencing devices ("next-generation sequencers", NGS), allowing them to analyze tens or hundreds of genes, or even the entire exome. This is having a major impact on medical concepts and practices, especially with respect to genetics and oncology. This ability to search for mutations simultaneously in a large number of genes is finding applications in the diagnosis of Mendelian diseases (including at birth), routine screening for heterozygotes, and pre-conception diagnosis. NGS is now sufficiently sensitive to analyze circulating fetal DNA in maternal blood (cell-free fetal DNA, cffDNA), enabling applications such as non invasive diagnosis of fetal sex (and X-linked diseases), fetal rhesus among rhesus-negative women, trisomy and, in the near future, Mendelian mutations. Data on multifactorial diseases are still preliminary, but it should soon be possible to identify "strong" factors of genetic predisposition that have so far been beyond the scope of genome-wide association studies (GWAS). In the field of constitutional oncogenetics, NGS can also be used for simultaneous analysis of genes involved in " hereditary " cancers (21 breast cancer genes, 6 colon cancer genes, etc.). More generally, NGS can identify all genomic abnormalities (deletions, translocations, mutations) in a given malignant tissue (hemopathy or solid tumor), and has the potential to distinguish between important mutations (those that drive tumor progression) from " bystander " or accessory mutations, and also to identify "druggable" mutations amenable to targeted therapies (e.g. imatinib and Bcr/Abl rearrangement; verumafemib and the BRAF V600E mutation). Systematic sequencing of all the genes involved in drug metabolism and responsiveness will lead to individualized pharmacogenetics. Finally, sequencing of the tumoral and constitutional genomes, identfication of somatic mutations, and detection of pharmacogenetic variants will open up the era of personalized medicine. The first results of these targeted therapeutic indications show a gain in the duration of remission and survival, although the cost-effectiveness of these approaches remains to be determined. Finally, this huge capacity for genome sequencing raises a number of regulatory and ethical issues.