The challenge for the next generation of medical geneticists.

Next-generation sequencing (NGS) has allowed a tremendous progress in the characterization of the molecular bases of genetic diseases and the last annual American Society of Human Genetics meeting has highlighted the implementation of whole exome sequencing in medical genetics. Several investigators suggest that it should be medically relevant for each individual to have the exome sequenced. These perspectives do not take into account the complexity of genetic variation interpretation and genetic determinism of human diseases: an important limiting step of targeted analyses of gene(s) involved in Mendelian diseases is already the interpretation of variants of unknown significance; most of the 20,000 single nucleotide variations present in each exome, even those having a very low allelic frequency, are not deleterious; the genetic determinism of the majority of human diseases involves either a combination of numerous genetic variations, each conferring a slightly increased risk, or rare genetic variations with a strong effect, but the demonstration of their involvement in diseases is particularly challenging. The challenge for the next generation of medical geneticists will be to integrate the technological power of NGS technologies, the complexity of genome interpretation, the importance of phenotyping before genotyping, and the guidelines of medical genetics raised in the pre-NGS era.