Science history: A tragic gene therapy death that stalled the field for a decade — Sept. 17, 1999

Twenty-six years ago today, on Sept. 17, a teenager who had received an experimental gene therapy died. His death led to needed changes in the clinical trial process while also spurring skepticism that would ultimately stall the field of gene therapy for years.

Jesse Gelsinger was an 18-year-old with ornithine transcarbamylase (OTC) deficiency, a genetic disease that affects about 1 in 40,000 newborns. The condition makes the body unable to make an enzyme that would normally break down ammonia, a natural waste product of metabolism. Without this enzyme, ammonia builds up in the body and poisons the blood.

About 90% of babies with the most severe form of OTC deficiency die. But Gelsinger — who had a milder, "late-onset" form of the disease — had reached adulthood by strictly adhering to a low-protein diet and a regimen of 50 pills a day, to help reduce the amount of ammonia in his blood and offset its effects. Although Gelsinger was small for his age and experienced a dangerous ammonia crisis when he stopped taking his pills, he was otherwise...