Ronald Crystal of the New York Hospital-Cornell Medical Center in Manhattan and Jeffrey Isner of Tufts University in Boston told The Washington Post in Wednesday's editions that they believe the six patients died from underlying illnesses and not from the gene therapy.
The Food and Drug Administration ordered Schering-Plough Corp. to temporarily halt new enrollments in two gene therapy studies last week after a teen-ager in a similar experiment died Sept. 16. University of Pennsylvania scientists had placed healthy genes in his liver to combat a rare metabolic disease.
The researchers in the blood vessel study said they did report the deaths to the FDA, which doesn't release the information. But they said federal regulations didn't require them to tell the NIH because gene therapy didn't directly cause the deaths.
The Post quoted NIH officials as saying that even deaths first appearing unrelated to gene therapy should be reported and made public because the cause of death may not be determined until later.
Isner told the Post not reporting the deaths was an oversight and he was unclear about whether he had to.
Crystal said he supported telling the NIH, but he didn't consider it a legal requirement. He said Parke-Davis, which sponsored his study, has become responsible for reporting deaths to the agencies involved.
Parke-Davis spokeswoman Carol Goodrich told the Post that the company had sent the NIH details of the deaths on Oct. 20.
The deaths had been discussed in scientific journals and meetings, both researchers said.