Purchase this article with an account.
Fred N. Ross-Cisneros, Carla Giordano, Valerio Carelli, Alfredo A. Sadun; Optic Neuropathy in a Case of Mitochondrial Neurogastrointestinal Encephalomyopathy (MNGIE): Ultrastructural Features and Mitochondrial DNA analysis. Invest. Ophthalmol. Vis. Sci. 2011;52(14):3872.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
To describe the ultrastructural (TEM) features and analyze the mitochondrial DNA (mtDNA) of postmortem optic nerve tissue from a patient with MNGIE, an autosomal recessive disease due to thymidine phosphorylase (TP) gene mutations characterized by mitochondrial DNA defects (deletions, depletion, and point mutations) in post-mitotic tissues secondary to thymidine accumulation.
Postmorten optic nerves from a MNGIE patient carrying a homozygous G1443A TP mutation and 12 age-matched controls were analyzed. Tissues were fixed in formalin and placed into two groups. One group was embedded in paraffin, sectioned, and placed on membrane slides for laser capture microdissection (LCM) for mtDNA analysis. Nerve bundles were microdissected in the 1) temporal, 2) nasal, and 3)central (with smooth muscle and endothelial cells from the central artery) areas. We evaluated mtDNA by real-time PCR, mtDNA deletions (5.0 kb, 7.7 kb, 8.1 kb and 9.5 kb) by long-range PCR, and mtDNA mutations by direct sequencing in selected regions. The other group was postfixed in glutaraldehyde, embedded in plastic, cut, placed on grids, and examined for ultrastructural features on a JEOL model JEM-2100 transmission electron microscope.
We failed to show accumulation of mtDNA deletions or point mutations in nerve bundles from the two quadrants, whereas a relative mtDNA depletion was found in the bundles surrounding the central artery in MNGIE as compared to controls(0.43 vs. 1.00 ± 0.1; mtDNA density per µm3) and depletion in smooth muscle and endothelial cells from the central artery (17.16 ± 5.3 vs. 130.93 ± 24.9; mtDNA copy/cell). Ultrastructurally, the MNGIE optic nerve revealed a large number of hypermyelinated axons, condensation of axoplasm, and glial cells showing various stages of cell injury and apoptosis.
In MNGIE, the mtDNA analysis suggests a major role played by vasculopathy associated with mtDNA depletion in the vascular wall, which may drive specific pathological features in other tissues. In the optic nerve, a mitochondrial pattern of temporal axonal loss was present in this patient, with the most peculiar finding of hypermyelination of the smaller axons. These findings suggest a possible influence of thymidine toxicity on myelin turnover, which may be relevant to the peculiar white matter abnormalities seen in brain MRI's of these patients.
This PDF is available to Subscribers Only