Purpose: To evaluate a group of patients with isolated, early-onset, bilateral optic neuropathy for genetic and biochemical evidence of mitochondrial diseases.
Methods: This case-control study involved 21 patients, 159 control subjects for mitochondrial (mt)DNA sequencing, and 40 control subjects for relative mtDNA content. Patients were identified who had had decreased vision since childhood due to bilateral optic neuropathy characterized by central visual loss with no other major neurologic or ocular abnormality and no clinical evidence of a mitochondrial syndrome. Clinical examination, electroretinograms, and neuroimaging were performed; the entire mtDNA coding region was sequenced in leukocytes of all patients; relative mtDNA content was assessed; and OPA1 and OPA3 nuclear genes associated with dominant and recessive optic atrophy, respectively, were sequenced. Main outcome measures were clinical description, nonsynonymous (NS) mtDNA nucleotide changes, relative mtDNA content, and OPA1 and OPA3 nucleotide changes.
Results: Twenty-one unrelated patients (16 male and 5 female; mean age at first examination 13.6 years) had bilateral moderate, relatively symmetric optic neuropathies and normal neurologic examinations other than strabismus in 11 and congenital nystagmus in 9. Four patients had optic nerve hypoplasia. One patient had the nt 11778 primary Leber hereditary optic neuropathy (LHON) mutation, and three others had mtDNA nucleotide changes predicted to be pathologic. The entire group had a small increase (6.7%) in relative mtDNA content of indeterminate statistical significance. No patient had a polymorphism or mutation of OPA1 or OPA3.
Conclusions: A minority of these young patients with sporadic bilateral optic neuropathy had abnormalities of the mitochondrial parameters evaluated. This bilateral optic neuropathy may be due to other genetic, epigenetic, or environmental injury to the optic nerve or to mitochondrial defects not studied.