A patient in the U.S. has become the first person to receive an injection of an experimental therapy meant to edit a genetic error in his DNA. The use of gene editing to correct cells in the body represents a scientific milestone, but the case also points to a troubling medical dilemma.
The patient, Brian Madeux, 44, of Arizona, is part of a clinical trial testing a gene-editing approach for Hunter syndrome, a type of metabolic disorder that slowly destroys the body’s cells. The life expectancy of people born with the disease is 10 to 20 years, so most patients are children. For now, the trial Madeux is enrolled in is only open to adults. So young patients who desperately need the therapy to survive will need to wait to get it.
The U.S. Food and Drug Administration often wants companies to show that a treatment is safe in adults before it can be used in children. Sangamo Therapeutics, the company conducting the trial, is aiming to treat nine adult patients before it can admit children into the current trial. But Sandy Macrae, CEO of Sangamo, says treating children at an early age is the ultimate goal.
“That’s where the real medical need is. We want to try to address this disease before any of the consequences happen, rather than in adult patients where many of the features are already fixed,” he says.
Hunter syndrome occurs mostly in boys and affects many different parts of the body. It’s caused by a mutation in a gene called IDS, which provides the instructions for making an enzyme that breaks down large sugar molecules in cells. When this gene is mutated, these sugar molecules build up within cells. This often causes enlarged tissues and organs, and in patients with a more severe type of the disease, it leads to cognitive decline and early death.
Weekly infusions of the deficient enzyme can ease some symptoms but do not improve brain function. The treatment, which takes about four hours to administer, can cost hundreds of thousands of dollars a year.
Though the exact number of people living with the disease is unknown, the Hunter Syndrome Foundation, a patient advocacy organization, estimates it at about 500 people in North America and 2,500 people worldwide. Jeanette Henriquez, who founded the Hunter Syndrome Foundation, says it will probably be difficult for Sangamo to find enough adult patients to test the therapy but is optimistic that it will eventually be tested in children.
“The community is very hopeful, and I am personally very hopeful about the results of this trial,” she says. Her seven-year-old son, Dominic, was diagnosed with the disease in 2011.
The Sangamo therapy uses a gene-editing technology called zinc finger nucleases rather than the newer CRISPR. It’s designed to insert a correct copy of the IDS gene into liver cells. Sangamo thinks this should enable the liver to produce a lifelong and stable supply of the enzyme the patient lacks.
Henriquez says that despite her optimism, she’d be reluctant to enroll her son in the trial if it became open to children, because gene editing comes with risks. A major worry is what happens if the editing machinery doesn’t get to the right part of the genome and instead makes unintentional cuts elsewhere.
Sangamo previously used its gene-editing technology to alter the cells of HIV patients outside the body and then infuse them back into the patient in hopes of eradicating the virus. The approach was supposed to make cells resistant to the virus. Macrae says the therapy is safe but was not effective enough to allow patients to stop taking their antiretroviral medicines, the common treatment for HIV.