Gene therapy for ocular problems in mucopolysaccharidosis: an experimental and promising approach with benefits in animal models - a review

Retinopathy in Mucopolysaccharidoses

PURPOSE

To determine the pattern(s) of onset, variation, and progression of retinopathy in patients with mucopolysaccharidoses (MPS).

DESIGN

Prospective, longitudinal, observational study.

PARTICIPANTS

Between November 2015 and March 2023, individuals with MPS were recruited from ophthalmology clinics at the Manchester Royal Eye Hospital, United Kingdom.

METHODS

Participants underwent assessment of visual acuity, corneal clouding, and intraocular pressure, along with fundoscopy, ultrawidefield (UWF) color fundus photography, fundus autofluorescence (FAF) imaging, OCT, and electroretinography (ERG), where feasible.

MAIN OUTCOME MEASURES

Evaluation of findings from clinical examination, retinal imaging, and ERG studies to ascertain the presence and patterns of retinopathy.

RESULTS

Data were collected for 75 patients, including 45 with MPS I, 9 with MPS II, 13 with MPS IVA, and 8 with MPS VI, aged 3 to 53 years. Fundus photography was conducted in 65 patients, FAF in 61 patients, OCT in 58 patients, and electrodiagnostic studies in 36 patients. Retinopathy was defined as signs of retinal disease evident through retinal examination or fundus photography, such as depigmentation, bone-spicule pigmentation, vascular tortuosity, retinal pigment epithelium (RPE) mottling/other changes, macular atrophy/puckering/epiretinal membranes, FAF findings such as a central hyperautofluorescent dot, hyperautofluorescent parafoveal ring, hypoautofluorescent lesions around fovea (double bull's eye), areas of hyper/hypoautofluorescence, and extrafoveal changes, OCT imaging features such as central external limiting membrane (ELM) thickening, RPE disturbance, photoreceptor layer loss, parafoveal retinal atrophy, and outer retinal/intrachoroidal cavities, or ERG studies revealing rod-mediated retinopathy or rod-cone dystrophy. Retinopathy was confirmed in 32 patients, including 25 with MPS I, 4 with MPS II, 1 with MPS IVA, and 2 with MPS VI. Five participants were first diagnosed with retinopathy with clinical examination, and 31 participants were identified on UWF color fundus photography supported by FAF and OCT. A total of 21 patients exhibited ERG abnormalities consistent with retinopathy. Fifteen of the total 32 participants described symptoms of nyctalopia. The onset of retinopathy varied substantially, with initial detection between 2 and 53 years of age.

CONCLUSIONS

Patients with MPS as young as 2 years may develop retinopathy, diagnosed through fundus examination, ophthalmic imaging, or ERG. Emerging treatments, including gene therapy, may prevent or stabilize retinopathy. Phenotypic data and natural history of MPS-related retinopathy are thus of paramount importance.

FINANCIAL DISCLOSURE(S)

Proprietary or commercial disclosure may be found after the references.

New Frontiers of Corneal Gene Therapy

Corneal diseases are among the most prevalent causes of blindness worldwide. The transparency and clarity of the cornea are guaranteed by a delicate physiological, anatomic, and functional balance. For this reason, all the disorders, including those of genetic origin, that compromise this state of harmony can lead to opacity and eventually vision loss. Many corneal disorders have a genetic etiology, and some are associated with rather rare and complex syndromes. Conventional treatments, such as corneal transplantation, are often ineffective, and to date, many of these disorders are still incurable. Gene therapy carries the promise of being a potential cure for many of these diseases, with solutions and strategies that did not seem possible until a few years ago. With its potential to treat genetic disease by means of deletion, replacement, or editing of a defective gene, the challenge can also be extended to corneal disorders in order to achieve long-term, if not definitive, relief. The aim of this paper is to review the state of the art of the different gene therapy approaches as potential treatments for corneal diseases and the future perspectives for the development of personalized gene-based medicine.

Gene therapy in the cornea: 2005--present

Successful restoration of vision in human patients with gene therapy affirmed its promise to cure ocular diseases and disorders. The efficacy of gene therapy is contingent upon vector and mode of therapeutic DNA introduction into targeted cells/tissues. The cornea is an ideal tissue for gene therapy due to its ease of access and relative immune-privilege. Considerable progress has been made in the field of corneal gene therapy in last 5 years. Several new gene transfer vectors, techniques and approaches have evolved. Although corneal gene therapy is still in its early stages of development, the potential of gene-based interventions to treat corneal abnormalities has begun to surface. Identification of next generation viral and nanoparticle vectors, characterization of delivered gene levels, localization, and duration in the cornea, and significant success in controlling corneal disorders, particularly fibrosis and angiogenesis, in experimental animal disease models, with no major side effects have propelled gene therapy a step closer toward establishing gene-based therapies for corneal blindness. Recently, researchers have assessed the delivery of therapeutic genes for corneal diseases and disorders due to trauma, infections, chemical, mechanical, and surgical injury, and/or abnormal wound healing. This review provides an update on the developments in gene therapy for corneal diseases and discusses the barriers that hinder its utilization for delivering genes in the cornea.