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The prevalence of genetic diseases, combined with their potential severity and chronic nature, imposes great human, social, and financial burdens on society. Human genetics refers to the study of individual genes, their role and function in disease, and their mode of inheritance. Genomics refers to an organism’s entire genetic information, the genome, and the function and interaction of DNA within the genome, as well as with environmental or nongenetic factors, such as a person’s lifestyle. With the characterization of the human genome, genomics complements traditional genetics in our efforts to elucidate the etiology and pathogenesis of disease and to improve therapeutic interventions and outcomes. Following impressive advances in genetics, genomics, and health care information technology, the consequences of this wealth of knowledge for the practice of medicine are profound and play an increasingly prominent role in the diagnosis, prevention, and treatment of disease (Chap. 84).

Personalized medicine, the customization of medical decisions to an individual patient, relies heavily on genetic information. For example, a patient’s genetic characteristics (genotype) can be used to optimize drug therapy and predict efficacy, adverse events, and drug dosing of selected medications (pharmacogenetics) (Chap. 5). The mutational profile of a malignancy allows the selection of therapies that target mutated or overexpressed signaling molecules. Although still investigational, genomic risk prediction models for common diseases are beginning to emerge.

Genetics has traditionally been viewed through the window of relatively rare single-gene diseases. These disorders account for ~10% of pediatric admissions and childhood mortality. Historically, genetics has focused predominantly on chromosomal and metabolic disorders, reflecting the long-standing availability of techniques to diagnose these conditions. For example, conditions such as trisomy 21 (Down’s syndrome) or monosomy X (Turner’s syndrome) can be diagnosed using cytogenetics (Chap. 83e). Likewise, many metabolic disorders (e.g., phenylketonuria, familial hypercholesterolemia) are diagnosed using biochemical analyses. The advances in DNA diagnostics have extended the field of genetics to include virtually all medical specialties and have led to the elucidation of the pathogenesis of numerous monogenic disorders. In addition, it is apparent that virtually every medical condition has a genetic component. As is often evident from a patient’s family history, many common disorders such as hypertension, heart disease, asthma, diabetes mellitus, and mental illnesses are significantly influenced by the genetic background. These polygenic or multifactorial (complex) disorders involve the contributions of many different genes, as well as environmental factors that can modify disease risk (Chap. 84). Genome-wide association studies (GWAS) have elucidated numerous disease-associated loci and are providing novel insights into the allelic architecture of complex traits. These studies have been facilitated by the availability of comprehensive catalogues of human single-nucleotide polymorphism (SNP) haplotypes generated through the HapMap Project. The sequencing of whole genomes or exomes (the exons within the genome) is increasingly used in the clinical realm in order ...

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