They used a “silent substitution” method using pairs of lights to target certain cones or rods for stimulation. The researchers also adapted their methods to accommodate another achromatopsia symptom known as nystagmus, or “dancing eyes,” and compared their results to tests that involved 28 volunteers with normal vision and nine untreated patients.
Six to 14 months after treatment, two of the four children showed strong evidence for cone-mediated signals in the brain’s visual cortex coming from the treated eye. The subjects had shown no evidence of cone function on any tests before the treatment. After treatment, on the other way, their measures were quite similar to those of the research participants who were normally sighted.
Subjects of the study also took a psychophysical test of cone function, which measures the eyes’ capacity to differentiate between various contrast levels. It indicated a difference in cone-supported vision in the treated eyes in the same two kids.
According to the researchers, they are unable to establish if the treatment was ineffective in the other two study subjects, whether there were treatment effects that their tests may not have detected, or whether effects were delayed.
“We are still analyzing the results from our two clinical trials to see whether this gene therapy can effectively improve everyday vision for people with achromatopsia. We hope that with positive results, and with further clinical trials, we could greatly improve the sight of people with inherited retinal diseases,” said Dr. Michel Michaelides, the co-lead author of the study.
The results of the study were published in the journal Brain.
Recent advances in regenerative therapy have placed the treatment of previously incurable eye diseases within arms’ reach. Achromatopsia is a severe monogenic heritable retinal disease that disrupts cone function from birth, leaving patients with complete color blindness, low acuity, photosensitivity and nystagmus. While successful gene-replacement therapy in non-primate models of achromatopsia has raised widespread hopes for clinical treatment, it was yet to be determined if and how these therapies can induce new cone function in the human brain. Using a novel multimodal approach, we demonstrate for the first time that gene therapy can successfully activate dormant cone-mediated pathways in children with achromatopsia (CNGA3- and CNGB3-associated, 10–15 years). To test this, we combined functional MRI population receptive field mapping and psychophysics with stimuli that selectively measure cone photoreceptor signaling. We measured cortical and visual cone function before and after gene therapy in four paediatric patients, evaluating treatment-related change against benchmark data from untreated patients (n = 9) and normal-sighted participants (n = 28). After treatment, two of the four children displayed strong evidence for novel cone-mediated signals in visual cortex, with a retinotopic pattern that was not present in untreated achromatopsia and which is highly unlikely to emerge by chance. Importantly, this change was paired with a significant improvement in psychophysical measures of cone-mediated visual function. These improvements were specific to the treated eye, and provide strong evidence for successful read-out and use of new cone-mediated information. These data show for the first time that gene replacement therapy in achromatopsia within the plastic period of development can awaken dormant cone-signaling pathways after years of deprivation. This reveals unprecedented neural plasticity in the developing human nervous system and offers great promise for emerging regenerative therapies.