Treatment Potential for LCA5-Associated Leber Congenital Amaurosis

PURPOSE. To determine the therapeutic window for gene augmentation for Leber congenital amaurosis (LCA) associated with mutations in LCA5. METHODS. Five patients (ages 6-31) with LCA and biallelic LCA5 mutations underwent an ophthalmic examination including optical coherence tomography (SD-OCT), full-field stimulus testing (FST), and pupillometry. The time course of photoreceptor degeneration in the Lca5(gt/gt) mouse model and the efficacy of subretinal gene augmentation therapy with AAV8-hLCA5 delivered at postnatal day 5 (P5) (early, n = 11 eyes), P15 (mid, n = 14), and P30 (late, n = 13) were assessed using SD-OCT, histologic study, electroretinography (ERG), and pupillometry. Comparisons were made with the human disease. RESULTS. Patients with LCA5-LCA showed a maculopathy with detectable outer nuclear layer (ONL) in the pericentral retina and at least 4 log units of dark-adapted sensitivity loss. The Lca5(gt/gt) mouse has a similarly severe and rapid photoreceptor degeneration. The ONL became progressively thinner and was undetectable by P60. Rod- and conemediated ERGs were severely reduced in amplitudes at P30 and became nondetectable by P60. Subretinal AAV8-hLCA5 administered to Lca5(gt/gt) mice at P5 and P15, but not at P30, resulted in structural and functional rescue. CONCLUSIONS. LCA5-LCA is a particularly severe form of LCA that was recapitulated in the Lca5(gt/gt) mouse. Gene augmentation resulted in structural and functional rescue in the Lca5(gt/gt) mouse if delivered before P30. Retained photoreceptors were visible within the central retina in all patients with LCA5-LCA, at a level equivalent to that observed in rescued Lca5(gt/gt) mice, suggesting a window of opportunity for the treatment of patients with LCA5-LCA.