Scientists Link Boy’s Brain Tumor to Gene Therapy Viruses

When a stem cell transplant failed for a 13-month-old boy with a life-threatening rare disease, doctors presented his parents with two options: a second transplant carrying a 10% to 15% risk of death or a new and untested gene therapy. The parents chose the gene therapy after witnessing complications from the first transplant, including an episode in which the boy could not breathe and required emergency intervention by nurses.

Following the treatment, the boy reached developmental milestones, learned sign language, and taught himself to read. Last year a routine scan revealed a golf-ball-sized tumor on his brain. Scientists have now linked the tumor to viruses used in the gene therapy, STAT reported on May 13, 2026.

The finding represents a rare case in which viruses from a gene therapy have been connected to a patient’s tumor. Doctors have stated that the risks of such treatments must be weighed against their potential benefits. The boy’s case highlights both the promise and the uncertainties surrounding gene therapies for rare diseases.

The initial stem cell transplant had failed, leaving the family to choose between a high-risk repeat procedure and an experimental approach that had not been previously tested in similar cases. The gene therapy initially appeared successful as the boy achieved milestones that had been in doubt.

The later discovery of the tumor introduced new questions about long-term safety of viral vectors used to deliver genetic material.

Gene therapies, including those using CRISPR and viral delivery systems, have advanced rapidly in recent years for treating rare genetic conditions. This case adds to the body of evidence that researchers review when assessing the safety profiles of these treatments.