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    A gene therapy clinical trial for achromatopsia

    By Prateek Buch, on 25 March 2013

    We are pleased to have been awarded a major research grant from the Medical Research Council (MRC), to develop gene therapy for achromatopsia. Affecting around  1/30000 people, achromatopsia is an inherited condition that causes the complete absence of colour vision from birth, a severe reduction in central visual acuity, extreme sensitivity to light and significant impairment of daylight vision from an early age.

    Roughly half of all achromatopsia cases in the UK are associated with damage to the CNGB3 gene – the 4 other genes associated with the disease are much rarer, making the CNGB3 form of the condition amenable to treatment.

    We will use the funding (£2.1 million) over the next five years to produce and test an engineered viral vector suitable for use in the clinic, and conduct a Phase I/II clinical trial of gene therapy in patients with achromatopsia caused by defects in the CNGB3 gene.

    In laboratory models, CNGB3 gene replacement using AAV is one of the most effective therapies being developed for sight loss caused by defects in the light-sensitive photoreceptor cells of the retina. In a study published in the journal Human Molecular Genetics we showed that gene delivery using an engineered adeno-associated virus (AAV) can restore vision in a model of achromatopsia lacking CNGB3. Our study showed long-term restoration of sight as measured by improvements in the ability of treated mice to track a visual stimulus. Dogs with a similar defect have been treated using AAV gene therapy by a group in the United States.

    As well as the MRC funding for the trial, we have secured ethical approval for the study from the National Research Ethics Committee (NRES). We will soon begin production and safety testing of the clinical grade virus to be used in the clinic, after which we can seek full regulatory approval from the Medicines and Healthcare products Regulatory Agency (MHRA) to begin the trial.

    We plan to use a different sub-type of AAV than in our previous gene therapy trial aimed at the RPE65 form of Leber congenital amaurosis (LCA). This sub-type has been shown to be more effective at delivering genes to the light-sensitive photoreceptors of the retina than the sub-type used in our previous gene therapy trial, which targeted a defect in the retinal pigment epithelium (RPE).

    Commenting on the prospect of a new trial for achromatopsia, Professor Robin Ali said: “This funding from the MRC is crucial for our programme. It will help us demonstrate that gene therapy can be used to treat photoreceptor cell defects, having shown it can be safe and effective in treating RPE defects.”

    We will provide further updates on progress towards a clinical trial for achromatopsia both here and on our website.