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Episode 4 : Curing CancerEpisode 4 : Curing Cancer

Special Report
Fixing Our Genes, by Magdalena Eriksson: Page 2 of 2
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In a Paris hospital in 2001, a group of young children who, like De Silva, suffered from SCID participated in a study. In these children, SCID was caused by a mutation in a gene called gamma-c. Through gene therapy, they received DNA with a flawless gamma-c gene, which was expected to stimulate the growth of immune cells in their bone marrow. For most of the children, the treatment was a success. The gamma-c gene became an established component of the children's bone marrow cells, and they were able to live normal lives.

Time passed and suddenly the good news turned dark. A year after the treatment, in October of 2002, one of the children developed leukemia. At first, doctors dismissed the incidence as bad luck, but when a second child, in January 2003, also developed leukemia, they began to look for the cause.

They learned that genes delivered through viruses prefer to integrate at active, loosely packed, portions of the genome, rather than at random sites. The new gene had inserted itself near a gene called LMO2, which plays a role in leukemia. This unexpected DNA insertion turned on the production of the LMO2 protein, which caused the development of leukemia.

Test tubes
The doctors had inadvertently discovered another factor to consider for making gene therapy safe.

The doctors had inadvertently discovered another factor to consider for making gene therapy safe. The two children have since recovered from their leukemia, but the experiment shows the risks required for scientists to make progress and steadily increase their knowledge.

The French trial also illustrates how complex our genetic systems are and how difficult it is to predict what will happen when we upset its fine-tuned balance. If you touch one gene, surprising connections with other genes may announce themselves in unexpected ways. The very principle behind gene therapy sets it apart from many other therapies. Once a new gene has become a permanent part of the genome in a cell, you may no longer have the option of discontinuing the treatment in case its effects prove detrimental. For some time to come, gene therapy may remain a double-edged sword.

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