Children, parents, and grandparents often share similar health problems. If a particular disease runs in your family, you may have inherited factors that put you at risk.
These factors are passed down from parent to child by way of genes. All humans have the same genes, but the information within each gene may differ slightly from person to person.
Sometimes genetic differences cause disease. In rare cases, changing a single gene is enough to cause disease. But more often disease results from the combined effects of minor changes in multiple genes. Each gene then contributes in a small way to the symptoms.
Prevalence of Common Diseases
It is estimated that heart disease, cancer and diabetes account for 7 of every 10 deaths in the United States. Like rare genetic disorders, these "common" diseases run in families and can therefore be considered genetic diseases. Because of this, a family history can provide important information about your family's risk of disease. But, is it possible to predict who will or will not develop disease? If so, how is this done?
Common diseases result from the combined effects of multiple genes and environmental factors. This makes it very difficult to predict whether or not an individual will inherit disease.
One reason for this is that the number of genes contributing to so-called "polygenic" diseases is usually not known. The number of genes carried by parents or children that can increase risk is also not known. And, environmental factors can greatly vary an individual's risk of developing disease.
Polygenic Disease Inheritance
Because more than one gene is involved in most common diseases, resulting inheritance patterns are varied and complex. If a parent has a disease, it does not necessarily mean a child will develop the same disease. So, risk can be estimated but not calculated.
Information in a family medical history must be used to assign an individual to a low, medium, or high risk group. This is done by comparing an individual's family history to data collected from large families affected by a disease. Persons in each risk group share characteristics that correlate with a certain probability of developing a disease.
What If I Don't Know My Family History?
Sometimes it's not possible to have access to medical information from your biological family. But it's still useful to complete a history using your guardian family. This is because family histories capture more than just genetic risk factors.
They also capture cultural, social, and environmental risk factors shared by a family that can contribute to disease.
Identifying Disease Genes
One goal of genetic research is to identify genes that contribute to these complex diseases, and understand how these genes are influenced by a person's environment.
Scientists are beginning to identify whole lists of genes that contribute to each of the major common adult diseases, such as heart disease, cancer and diabetes.