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Genetic research sheds light on common complex diseases


This article is part of a series that will bring the latest genetic developments from the National Human Genome Research Institute to practicing nurses.

Have you read the science or medical section of a newspaper, journal, or online news source lately? Chances are, it includes an item about a new genetic discovery.
Five years ago, the typical genetics-related news story reported a discovery about a rare genetic disorder. Today, it’s more likely to reveal that scientists have found one or more genes contributing to a common complex disorder.

Information windfall
Has the genetics research community at long last recognized the importance of understanding the genetic bases of common diseases? No. The change in focus reflects the fact that researchers only recently developed tools that allow us to successfully study complex disorders—those, like prostate cancer, in which genes and the environment strongly interact. (See Genes and prostate cancer in PDF format by clicking the download now button.)
Several factors converged to bring us this information windfall, including the decreasing cost of DNA sequencing and completion of the International HapMap project, a tool for studying the human genome. Various genes and environmental factors influence the development of most common diseases, including cancer, diabetes, heart disease, and asthma. Finding the DNA sequence variants that contribute to common disease risk is crucial to understanding the complex causes of disease.
Taking the GWAS approach
Researchers can now look at statistical associations between disease status and large numbers of genetic variants across the genome in large numbers of people. Work that 5 years ago would have required tens of millions of dollars, several large laboratories, and years to complete now can be done by one laboratory group in less than 1 year for under $1 million.
This approach to learning about the genetics of common complex disorders is known as a genome-wide association study (GWAS). Properly applied, it can detect common genetic variants that contribute to small increases in disease risk in any one individual. Already, the scientific yield has been enormous and the end isn’t in sight.
How—and how quickly—will the data translate to clinical applications? At least one company has developed and plans to market a genetic test that predicts the risk of developing prostate cancer, based on a panel that includes five genetic markers. Numerous companies are targeting newly identified genes for rational drug design. Studies are underway to examine how testing patients with panels of genetic risk markers for multiple common diseases may improve patient care and determine how patients react to such testing.

Nurses on the cutting edge
Can patients be tested today based on what we have learned from GWAS-type studies? Yes. Should such testing be done? That remains to be seen, as researchers haven’t determined if such information is useful in clinical practice. We don’t yet know if the tests are valid or whether knowledge of test results will influence patient healthcare practices. What’s apparent is that this tide of genetic information ultimately will strongly influence patient care—and nurses in primary care settings will be on the cutting edge.

Selected references
American Cancer Society. Detailed guide: prostate cancer. www
.cancer.org/docroot/CRI/CRI_2_3x.asp?rnav=cridg&dt=36. Accessed October 17, 2008.
Eeles RA, Kote-Jarai Z, Giles GG, et al. Multiple newly identified loci associated with prostate cancer susceptibility. Nat Genet. 2008;40(3):316-321.
Gudmundsson J, Sulem P, Rafnar T, et al. Common sequence variants on 2p15 and Xp11.22 confer susceptibility to prostate cancer. Nat Genet. 2008;40(3):281-283.
National Cancer Institute. Prostate cancer. www.cancer.gov/cancertopics/types/prostate. Accessed October 17, 2008.
National Human Genome Research Institute. Genome-wide association studies. www.genome.gov/20019523. Accessed October 17, 2008.
Thomas G, Jacobs KB, Yeager M, et al. Multiple loci identified in a genome-wide association study of prostate cancer. Nat Genet. 2008;40(3):310-315.

Dale Halsey Lea is a Health Educator with the Education and Community Involvement Branch of the Genomic Healthcare Branch at the National Human Genome Research Institute in Bethesda, Maryland. Greg Feero is a Family Physician and Chief of the Genomic Healthcare Branch. Jean F. Jenkins is a Senior Clinical Advisor at the Genomic Healthcare Branch.

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