[Next Generation Sequencing (NGS) for beginners]

Genetic diagnoses have progressed through the development of Next Generation Sequencing (NGS), which enables improved patient care and more precise genetic counseling. NGS techniques analyze DNA regions of interest in view accurately determining the relevant nucleotide sequence. Different kinds of analysis apply NGS : multigene panel testing, Whole Exome Sequencing (WES) and Whole Genome Sequencing (WGS). While regions of interest depend on the type of analysis (multigene panels testing studies the exons of genes implicated in a particular phenotype, WES studies all exons of all genes, and WGS studies all exons and introns), the technical protocol remains similar. Clinical/biological interpretation is based on a body of evidence allowing categorization of variants into five groups (from benign to pathogenic) in accordance with an international classification, which takes into account segregation criteria (variant detected in affected relatives, but absent in healthy relatives), matching phenotype, databases, scientific literature, prediction scores and data drawn from functional studies. Clinical/biological interaction and expertise are essential during this interpretative step. Pathogenic and probably pathogenic variants are returned to the clinician. Variants of unknown significance can likewise be returned, if they are liable to be reclassified through further analysis as pathogenic or benign. Variant classifications may change, as new data emerge suggesting or ruling out pathogenicity.