Global Connections to Study Idiopathic Macular Telangiectasia Type 2

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Idiopathic macular telangiectasia Type 2 (Mac Tel Type 2), once a poorly characterized and understood retinovascular entity, is the disease studied in a group of papers published in the current issue of Retina. Although considered a rare ocular condition, our understanding of Mac Tel Type 2 has increased significantly since it was first described by Gass and Oyakawa in 1982.1 To a large extent, this increased understanding and awareness can be attributed to the establishment of a large, multinational collaborative research project focusing on Mac Tel Type 2. This effort grew out of a meeting held in 2004 in response to a family's request to determine whether there was work that could be done to better understand, and find a treatment for, MacTel Type 2. The affected family member had a delayed diagnosis but, ultimately, was appropriately referred and diagnosed. (Mac Tel Type 2 is frequently misdiagnosed, most commonly as macular degeneration due to the pigmentary abnormalities and retinal telangiectasia and/or outer retinal neovascularization.) In search for a correct diagnosis and information about the disease, the patient and his family learned that little was known about MacTel Type 2, and, furthermore, there was no treatment and no active research ongoing. Not content to be given a diagnosis of a disease about which very little was known and no treatments available, the patient and his family decided to fund a program that became known as the MacTel Project. Both clinical and basic science research has been well supported to study this condition. In the spirit of full disclosure, the authors of this editorial are active participants in this international collaborative research project generously funded by the Lowy Medical Research Institute to investigate the pathogenesis and to find potential treatments for Mac Tel Type 2. Currently, there are no proven effective therapies for Mac Tel Type 2.
This group of investigators has collaborated since 2005 by conducting the largest observational longitudinal study of Mac Tel Type 2 to date.2–5 This project has evolved over the decade with strong interactions and collaboration between the clinicians from 31 international clinical sites and investigators from a dozen basic science laboratories located in the United States, Europe, and Australia. Mac Tel type 2 characteristic lesions include retinal opacification, perifoveal telangiectatic vessels that leak on fluorescein angiography, right angle vessels and crystalline deposits (Figure). With more advanced disease, retinal pigment epithelial hyperpigmentation occurs, quite often along the right-angle vessels. Abnormalities are seen on fundus autofluorescence imaging, as well as on spectral domain optical coherence tomography, where hypo-reflective inner and outer retinal cavities, as well as ellipsoid zone or inner segment/outer segment losses, are found. Macular pigment loss is also evident. Less frequently, neovascularization originating from the retinal circulation can occur, forming retinal-choroidal anastomoses.
The MacTel research group has also made significant efforts to study genetic, high resolution imaging, and metabolomics. In addition, significant efforts are ongoing to study genetic, high resolution imaging, and metabolomics related to Mac Tel Type 2. This condition, once thought be vascular in origin, is now considered a neuro/vasculo/glial degenerative disease. This concept is supported by clinical data from in vivo adaptive optics imaging6 and studies of autopsy eyes from patients with Mac Tel Type 2.7,8 More recently, genetic and metabolomic studies suggest that MacTel may have a genetic/metabolic component with a defect in serine/glycine metabolism.9
This clinical research group followed a cohort of affected individuals in a natural history study and completed both Phase 110 and Phase 2 clinical trials in Mac Tel Type 2 using a ciliary neurotrophic factor implant.
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