Two for One

Leber hereditary optic neuropathy (LHON) patients taking part in a phase 3 clinical trial received injections of a gene therapy vector into the vitreous cavity of one eye. As a result, 78 percent unexpectedly noted significant improvement of visual function in both eyes. Even more surprisingly, both eyes followed the same trajectory over two years of follow-up. The effect is possibly due to the viral vector DNA transferring from the injected eye into the other; the DNA was detected in the anterior segment, retina, and optic nerve of the untreated eye three months after injection. The therapy saves retinal ganglion cells from a mutation that causes LHON by replacing the defective gene. Once the mechanism of the bilateral improvement is better understood, it could potentially be used with other sight-saving gene therapies.