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What Are the Pros and Cons of Gene Therapy for SCID?

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  • Written By: Marlene Garcia
  • Edited By: Daniel Lindley
  • Last Modified Date: 11 November 2016
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Severe combined immunodeficiency (SCID) treated via gene therapy proved successful for curing the disease but caused leukemia in some infants in the 1990s. Four of nine children treated with gene therapy for SCID in European experiments developed blood cancer several years after treatment. Newer studies show promise that gene therapy for SCID might be successful without causing cancer.

Gene therapy involves introducing a genetically altered virus, called a vector, into the bone marrow of a patient. A sample of bone marrow is removed from the sick infant before genes containing the virus are added in a laboratory. After the altered bone marrow is reintroduced into the patient’s body, it begins creating the missing genetic link that causes SCID.

Using gene therapy for the disease ceased after four of the European children developed leukemia. One of the children died after leukemia treatment failed, sparking controversy over gene therapy for SCID. Scientists found the genetic material altered in the laboratory disrupted the normal functioning of a nearby gene that causes cancer, but eight of the nine surviving patients recovered to live normal lives.

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When the immune system fails to function properly, the body cannot fight viral or bacterial infection from common illnesses. Without gene therapy for SCID, or bone marrow transplants, most children die before their first birthdays. Bone marrow transplants represented the only available treatment for the disorder before scientists discovered gene therapy for SCID. Problems with bone marrow transplants centered on finding suitable donors to decrease the odds of rejection by the body.

Before gene therapy for SCID existed, a baby born with the disease was isolated to prevent exposure to germs. In the 1970s, the disorder gained international attention when doctors confined David Vetter to a sterile environment after birth while searching for a viable bone marrow donor. The infant was referred to as the boy in the bubble, prompting the disease to be called bubble boy syndrome.

David Vetter died in 1984 after receiving a bone marrow transplant from his older sister. Her bone marrow partially matched her sibling’s, but a mutation caused the development of Epstein-Barr virus. Researchers began experimenting with gene therapy for SCID after the boy’s death. They discovered using the patient’s own bone marrow eliminated the chance of rejection present in bone marrow transplant operations.

After the European children treated with gene therapy developed leukemia, scientists began looking for ways to perfect the vector virus without causing cancer. As of 2011, new methods of gene therapy for SCID were approved for trial experiments. Human trials include monitoring study participants for 15 years to measure the effectiveness of new treatment methods.

Ten forms of SCID exist, identified by which cells are missing in newborn babies. Considered a rare disease, it is passed to offspring by parents who carry defective genes, with more boys affected than girls. Children born with the condition typically face death when infected by germs that cause illnesses common in childhood.

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