The findings of the trial, which involved a handful of patients with the rare and often fatal genetic condition, Hunter syndrome, were reported at the annual meeting of the Society for the Study of Inborn Errors of Metabolism in Athens. The results also suggest that the treatment may potentially be effective at higher doses.
'It’s still very early in the clinical trial to be too positive,' Dr Joseph Muenzer, leading the study at the University of North Carolina, Chapel Hill, told the Associated Press. 'But at the same time, I am still very encouraged by what we have seen to date.'
People with Hunter syndrome lack a gene responsible for making an enzyme that breaks down complex sugars called mucopolysaccharides. These sugars build up in cells throughout the patient's body, causing damage to many organs, including the brain, lungs and heart.
Researchers treated four patients with an infusion containing many healthy copies of the gene for the dysfunctional enzyme, along with zinc finger nucleases. These are enzymes that insert the new gene in a precise region of the patient's DNA. The genome editing treatment was targeted at the liver, where the enzyme is normally produced.
In two patients who received a medium dose of the treatment, the levels of large sugar compounds in their urine decreased by half after 16 weeks. Little change was seen in urine sugar level in the two patients who received a low dose. There were no reports of any serious side effects linked to the therapy. However, it is too early to know for certain how effective the treatment is, the researchers caution.
The scientists remain optimistic and higher doses of the treatment are now being tested in two more patients. The results could have implications for a broad range of diseases. But Dr Muenzer added that sustained, reduced levels of sugars are necessary for the treatment to be a practical option for patients.
Dr Matthew Porteus, a genetics expert at Stanford University, California, who was not involved in the study, said the researchers needed to monitor in the longer term how the patients' immune systems continue to react to the treatment and whether the effects last. 'I would be excited about continuing to push along based on these results,' he concluded.