Purpose: To assess the functional significance of the mitochondrial nt-9957 mutation in a man with non-arteritic ischemic optic neuropathy (NAION). This nt-9957 mutation has been previously reported in association with mitochondrial encephalopathy, lactic acidosis, and stroke-like events (MELAS).
Methods: The patient was examined clinically and with magnetic resonance imaging and spectroscopy. The entire coding region of the mitochondrial genome was sequenced, and mitochondrial function was assessed by flow cytometry after staining with fluorescent dihydroethidium.
Results: This 76-year-old man had optic nerve disease bilaterally and seizures, but no clinical or radiological evidence of MELAS. He had no mitochondrial DNA mutation other than the 9957. Functional testing revealed a severe defect in mitochondrial complex III activity.
Conclusions: This patient had a mitochondrial functional deficit consistent with his 9957 mutation. It seems quite likely that this mutation may be responsible for optic nerve and brain injuries.