The federal government has ordered Schering-Plough Corp. to temporarily halt two gene therapy studies because the research design is similar to a Pennsylvania experiment in which a teenager died last month.

No one yet knows what killed Jesse Gelsinger, 18, of Tucson. Just four days before his death, University of Pennsylvania scientists had placed healthy genes in his liver to combat a rare metabolic disease. Penn's study has been halted while scientists there, along with federal regulators, try to determine what went wrong.

The Food and Drug Administration decision late Friday halts two separate experiments by Schering-Plough to try gene therapy as a treatment for liver cancer and for colorectal cancer that spreads to the liver.

Those studies have one similarity to the Penn experiment that worried regulators: They use relatively high doses of a type of cold virus called adenovirus to slip new genes directly into the liver.

No deaths or unexpected side effects have been reported in the Schering trials, but the studies' suspension is a precaution to let the FDA scrutinize patient data for any early signs of problems, FDA gene therapy chief Philip Noguchi said yesterday. The FDA wants to see "if there's any pattern we might be able to understand, to give us some insight into the Penn study," he said.

The FDA suspension means Schering cannot enroll any new patients, but patients already given their first gene dose can receive the rest of their scheduled treatment, said company spokesman Robert Consalvo.

The FDA decision does not affect dozens of other gene therapy experiments that use lower doses of adenoviruses or that inject them into some organ other than the liver.