Scientists at Duke University say some of the genes people inherit from their parents are, in effect, turned off.
The researchers say that means people may be more vulnerable to a number of problems ranging from obesity to cancer.
Duke scientists have identified the "silenced genes," creating the first map of the unique group of about 200 genes thought to play a profound role in people's health.
The finding will help study how environmental factors such as food, stress and pollution interact with genes to help determine why some people get sick and others do not.
The findings were published online today by the Journal Genome
Lead researcher Randy Jirtle says work will begin on exactly what roles the genes play.