Whole-Exome/Genome Sequencing and Genomics

As medical genetics has progressed from a descriptive entity to one focused on the functional relationship between genes and clinical disorders, emphasis has been placed on genomics. Genomics, a subelement of genetics, is the study of the genome, the sum total of all the genes of an organism. The human genome, which is contained in the 23 pairs of nuclear chromosomes and in the mitochondrial DNA of each cell, comprises >6 billion nucleotides of genetic code. There are some 23 000 protein-coding genes, a surprisingly small fraction of the total genetic material, with the remainder composed of noncoding DNA, regulatory sequences, and introns. The Human Genome Project, launched in 1990, produced a draft of the genome in 2001 and then a finished sequence in 2003, on the 50th anniversary of the initial publication of Watson and Crick's paper on the double-helical structure of DNA. Since then, this mass of genetic information has been translated at an everincreasing pace into useable knowledge applicable to clinical medicine. The recent advent of massively parallel DNA sequencing (also known as shotgun, high-throughput, and next-generation sequencing) has brought whole-genome analysis into the clinic for the first time, and most of the current applications are directed at children with congenital conditions that are undiagnosable by using standard genetic tests for single-gene disorders. Thus, pediatricians must become familiar with this technology, what it can and cannot offer, and its technical and ethical challenges. Here, we address the concepts of human genomic analysis and its clinical applicability for primary care providers.