'Silenced' Genes

Remember biology class where you learned that children inherit one copy of a gene from mom and a second from dad? There's a twist: Some of those genes arrive switched off, so there is no backup if the other copy goes bad, making you more vulnerable to disorders from obesity to cancer.

Duke University scientists now have identified these "silenced genes," creating the first map of this unique group of about 200 genes believed to play a profound role in people's health.

More intriguing, the work marks an important step in studying how our environment — food, stress, pollution — interacts with genes to help determine why some people get sick and others do not.

"What we have is a bag of gold nuggets," lead researcher Dr. Randy Jirtle said about the collection of "imprinted" genes. The team's findings were published online Friday by the journal Genome Research.

Next comes work to prove exactly what role these genes play. "Some will be real gold and some will be fool's gold," Jirtle added.

Usually, people inherit a copy of each gene from each parent and both copies are active, programmed to do their jobs whenever needed. If one copy of a gene becomes mutated and quits working properly, often the other copy can compensate.

Genetic imprinting knocks out that backup. It means that for some genes, people inherit an active copy only from the mother or only from the father. Molecular signals tell, or "imprint," the copy from the other parent to be silent.

Jirtle compared it to flying a two-engine airplane with one engine cut off. If the other engine quits, the plane crashes. In genetic terms, if one tumor-suppressing gene is silenced and the active one breaks down, a person is more susceptible to cancer.

Only animals that have live births have imprinted genes. It was not until 1991 that it was proved that humans had them. Until now, only about 40 human imprinted genes had been identified.

The Duke map verified those 40 and identified 156 more. Researchers fed DNA sequences into a computer program that decoded patterns pointing to the presence of imprinted genes instead of active ones.