The Food and Drug Administration didn't reveal the cause of death or any details about the patient, who had enrolled in a study of gene therapy for advanced arthritis. The agency said it was investigating what role, if any, therapy played in the death, which occurred Tuesday.
It marks the third blow since 1999 to the field of gene therapy, as scientists struggle to determine if the viruses they use to deliver new genes may themselves cause serious trouble.
Twenty-eight other gene therapy studies have been reported to the FDA that used, or are using, the same virus, called adeno-associated virus or AAV.
The FDA said Thursday that it was not aware of any serious side effects in any of those studies but that as a precaution, officials were reviewing all the ones still actively treating patients.
Targeted Genetics Corp. notified the FDA of the patient's illness and subsequent death.
The company had enrolled more than 100 people in the study without similar problems, but this patient became ill after a second injection of the therapy directly into an arthritic joint, the FDA said.
The therapy uses AAV to deliver a gene that in turn blocks tumor necrosis factor, a substance that fuels the joint inflammation behind crippling forms of arthritis. Drugs that block TNF already are widely used to treat rheumatoid arthritis and other conditions, but a gene therapy approach is novel.
"We are deeply saddened by the death of an individual enrolled in our clinical trial," company president H. Stewart Parker said in a statement issued Thursday.
The company didn't immediately return a phone call seeking comment.
In 1999, 18-year-old Jesse Gelsinger died in his fourth day of a gene therapy experiment at the University of Pennsylvania. Gelsinger had suffered from an inherited disorder that blocks the body from properly processing nitrogen. The FDA concluded that the gene therapy injection intended to try to cure him instead killed him.
That gene therapy attempt used a cousin to AAV, called adenovirus, to deliver the needed gene.
The only disease ever to be cured with gene therapy is "bubble boy disease," an immune disorder formally called severe combined immunodeficiency, or SCID. But gene therapy attempts are restricted to SCID patients who have no alternative, after doctors in 2003 discovered a few babies saved by gene therapy went on to develop cancer -- again, linked to the virus used to deliver the genes.
Reflecting how seriously regulators take this latest death, the National Institutes of Health's advisory committee on gene therapy will meet in September to discuss its potential scientific implications. E-mail to a friend 
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Huge surprise. My suspicions were correct!