When you have a genetic mutation, you have a permanent change in the DNA sequence of that gene. Some genetic mutations can be passed on to your children. This is referred to as a germline mutation and is made possible only when the mutation targets genes inside the cells responsible for making sperm and eggs. Once it's passed on to you by a parent, it appears in nearly all of your body's cells. Not all mutations cause disease, however.
It might take other factors that you can control -- often called environmental factors -- to cause the disease or condition to develop. For example, heart disease, high blood pressure or diabetes may run in your family. These disorders likely are caused by problems in more than one gene and studying these patterns in your family history can help genetics professionals predict susceptibility of you and your descendants. More importantly, monitoring your exposure to other risk factors for these diseases, such as tobacco smoke, poor diet or exercise is not only a positive for you, but also for your descendants. Of course, the extent to which environment or genetics play a role in the effects of a mutation varies considerably from one person and situation to another.
For some genetic conditions and disorders, as the mutations pass from one generation to another, the signs and symptoms might become more severe and appear at earlier ages than they did in the previous generations. This is called genetic anticipation [source: National Institutes of Health].
People may mistakenly believe that a particular disorder is inherited or miscalculate their chances; estimating risk is complicated. Today's genetic testing and counseling is increasingly sophisticated. A professional can look at your family history to help determine whether a disorder is connected to a genetic mutation that will pass to your children and future generations. As scientists learn more about the human genome and about genetic mutations, they also are able to more specifically understand why some people in families with mutations, such as the BRCA gene mutation for breast cancer, get the disease and others do not. They also are better able to target treatments for genetically based diseases.
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