BACKGROUND AND PURPOSE:Brain white matter is frequently affected in mitochondrial diseases;
optic atrophy gene 1-autosomal dominant optic atrophy and Leber hereditary optic neuropathy are the most frequent mitochondrial monosymptomatic optic neuropathies. In this observational study, brain white matter microstructure was characterized by DTI in patients with
optic atrophy gene 1-autosomal dominant optic atrophy and Leber hereditary optic neuropathy, in relation to clinical and genetic features.
MATERIALS AND METHODS:Nineteen patients with
optic atrophy gene 1-autosomal dominant optic atrophy and 17 with Leber hereditary optic neuropathy older than 18 years of age, all genetically diagnosed, and 19 healthy volunteers underwent DTI by using a 1.5T MR imaging scanner and neurologic and ophthalmologic assessments. Brain white matter DTI metrics were calculated for all participants, and, in patients, their correlations with genetics and clinical findings were calculated.
RESULTS:Compared with controls, patients with
optic atrophy gene 1-autosomal dominant optic atrophy had an increased mean diffusivity in 29.2% of voxels analyzed within major white matter tracts distributed throughout the brain, while fractional anisotropy was reduced in 30.3% of voxels. For patients with Leber hereditary optic neuropathy, the proportion of altered voxels was only 0.5% and 5.5%, respectively, of which half was found within the optic radiation and 3.5%, in the smaller acoustic radiation. In almost all regions, fractional anisotropy diminished with age in patients with
optic atrophy gene 1-autosomal dominant optic atrophy and correlated with average retinal nerve fiber layer thickness in several areas. Mean diffusivity increased in those with a missense mutation. Patients with Leber hereditary optic neuropathy taking idebenone had slightly milder changes.
CONCLUSIONS:Patients with Leber hereditary optic neuropathy had preferential involvement of the optic and acoustic radiations, consistent with trans-synaptic degeneration, whereas patients with
optic atrophy gene 1-autosomal dominant optic atrophy presented with widespread involvement suggestive of a multisystemic, possibly a congenital/developmental, disorder. White matter changes in Leber hereditary optic neuropathy and optic atrophy gene 1
-autosomal dominant optic atrophy may be exploitable as biomarkers.Mutations in
optic atrophy gene 1 are the main cause of autosomal dominant optic atrophy (DOA) (Online Mendelian Inheritance in Man 605290).
1,2 DOA is characterized clinically by insidiously progressive visual loss in childhood, centrocecal scotoma, dyschromatopsia, and temporal or diffuse pallor of the optic discs, due to selective loss of retinal ganglion cells leading to atrophy of the optic nerve.
1,2 Similarly, Leber hereditary optic neuropathy (LHON) (Online Mendelian Inheritance in Man 535000) is characterized by subacute loss of central vision, dyschromatopsia, and optic atrophy due to maternally inherited point mutations in mitochondrial DNA that affect respiratory complex I.
1,2DOA and LHON represent the so-called nonsyndromic mitochondrial optic neuropathies, characterized by optic nerve atrophy as the only or at least prevalent pathologic feature with an early and preferential involvement of the small fibers in the papillomacular bundle.
3,4 Recent MR imaging studies by using voxel-based morphometry,
5 DWI,
6 and DTI
7 have also indicated abnormalities of the optic radiation in patients with LHON, confirmed by postmortem investigation,
6 suggesting a trans-synaptic degeneration. A similar secondary involvement of the retrogeniculate visual pathway could also be hypothesized in patients with DOA. Furthermore, given that the
optic atrophy gene 1 (
OPA1) is highly expressed in the retina but also in the brain
1,2,8 and that a subgroup of patients with specific
OPA1 mutations have a multisystem neurologic disorder,
9 it is reasonable to also hypothesize a subclinical extravisual brain involvement in patients with
OPA1-DOA.The aim of the present study was to investigate the brain white matter of patients with
OPA1-DOA compared with those with LHON and healthy controls, by using a voxelwise analysis of DTI, which can disclose abnormal water diffusivity in brain areas where atrophy and/or gliosis occur,
10 to look for subtle structural alterations.
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