Race, Genetics, and the Environment—A Complicated Equation
Some diseases are more common in one race than another. For example, African Americans are more prone to ]]>diabetes]]> and ]]>prostate cancer]]> than Caucasians. ]]>Osteoporosis]]>, however, strikes Asian American and Caucasian women more often than African American women. Recent data suggest ]]>Parkinson’s disease]]> is more common in Hispanics than in other ethnic groups.
Scientists and doctors have tried to learn why certain diseases hit some ethnic groups harder than others. Usually the question is posed as nature versus nurture, or heredity versus environment. But as yet, we still don’t know which plays a greater role.
The Interaction Between Genes and the Environment
Georgia Dunston, PhD, a geneticist and the director of the National Human Genome Center at Howard University looks at the nature versus nurture issue somewhat differently. When looking at similarities in an ethnic group or race, she doesn’t try to separate genetics from environment. Instead she says, “We are seeing the interaction between genetic variation and the environment.”
To understand how genes and the environment interact, we need to understand a little about the theory of genetic evolution. Throughout human history, genes are passed down from one generation to the next. But we don’t end up with exactly the same genes as our parents or grandparents. Genes from each parent are scrambled together for each new baby. New combinations form. Sometimes genes change to produce new genes that are not seen in either the mother nor the father. If the new gene is helpful for the baby in its environment, that baby may be healthier or live longer.
A Gene and Environment Example
For an example of the interaction between genes and the environment, let’s look at ]]>sickle cell anemia]]>. Sickle cell anemia is a blood disease seen mostly in African Americans. In sickle cell anemia some red blood cells are irregularly shaped. Those cells cannot move freely throughout the body.
It turns out that there is one particular change in the gene that regulates the red blood cell shape. Scientists believe that this gene change emerged thousands of years ago in people who lived in areas like Africa that were plagued by ]]>malaria]]>. People who had one copy of this new gene actually survived malaria better than people who did not have this gene. The people who survived then handed this changed gene down to their children and their children’s children.
This gene continued to be passed down from generation to generation of Africans. This sets the genetic stage for the development of sickle cell anemia in people who inherited two copies of the gene.
Other Types of Environmental Influences
While a change in just one gene causes sickle cell anemia, most chronic diseases are the result of many genes interacting with many environmental influences. These environmental influences may include:
- Chemicals in the environment
- Living situations
- Different foods we eat
Even psychological perceptions and stressors may be important in promoting disease in people with certain genes, says Dunston. Trying to separate the impact of each genetic change from each environmental factor can get quite complicated.
Over time, gene changes that can help people survive better in a particular environment become widespread in a population. Then if a population marries mostly within itself, as most races or ethnic backgrounds do, those genes remain within that race. But if the environment people live in changes, gene variations that were helpful in one environment may not be helpful in another environment. In new situations, some gene changes may even increase the risk of getting another disease.
Environment and the Individual
Simply having a gene change passed down in a population does not mean each person of that population will get sick. For most diseases, the current environment a person lives in still influences whether he or she gets sick. Even with sickle cell anemia, the environment continues to play a role. A person with sickle cell anemia may feel well until they encounter an unusual situation like getting dehydrated or being in extremely hot or cold temperatures. Then they may become severely ill. So, in essence, while it is our genes that put us at risk, our environment influences whether we are healthy or not.
The new field of genomics studies how all of our genes work together. Dunston and other scientists hope future research in genomics will continue to sort out why different populations of people sometimes contract diseases at different rates. Genomic studies of families and ethnic populations in particular should provide more answers. In fact, researchers at Howard University are studying genomic variation and environmental information from African American families to help map their genetic risks for prostate cancer and diabetes.
Environment and genetics both impact why certain people are more prone to some diseases rather than others. We look to future research to provide more information on our genes, our environments, and how we all can stay as healthy as possible.
National Human Genome Center at Howard University
US Centers for Disease Control and Prevention, National Office of Public Health Genomics
BC Health Guide
Burchard EG, Ziv E, Coyle N, et al. The importance of race and ethnic background in biomedical research and clinical practice. N Engl J Med. 2003;348:1170-1175.
Centers for Disease Control and Prevention website. Available at http://www.cdc.gov/. Accessed on June 12, 2003.
Cooper RS, Kaufman JS, Ward R. Race and genomics. N Engl J Med. 2003;348:1166-1170.
Doris PA Hypertension genetics, single nucleotide polymorphisms, and the common disease: common variant hypothesis. Hypertension. 2002;39:323-331.
National Heart, Lung, and Blood Institute website. Available at: http://www.nlm.nih.gov/. Accessed on June 12, 2003.
National Institutes of Health Osteoporosis and Related Bone Diseases website. Available at: http://www.osteo.org/. Accessed on June 13, 2003.
Last reviewed March 2008 by ]]>Mark A. Best, MD, MPH, MBA ]]>
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