Brainstem involvement in Leber's hereditary optic neuropathy: association with the 14,484 mitochondrial DNA mutation

Axonal degeneration in peripheral nerves in a case of Leber hereditary optic neuropathy

BACKGROUND

Leber hereditary optic neuropathy (LHON) is a mitochondrial DNA (mtDNA) genetic disorder characterized by profound bilateral loss of central vision due to selective loss of retinal ganglion cells. Most patients with LHON do not have complaints related to the peripheral nervous system. We investigated possible qualitative and quantitative histological changes in the peripheral nerve of a patient with LHON as compared to normal controls.

METHODS

Brachial plexus specimens were obtained at necropsy from a patient with LHON carrying the 3460/ND1 mtDNA mutation and age-matched controls without known history of neurological disease. The nerves were evaluated by light microscope coupled to a digital camera-based morphometric analysis and electron microscopy.

RESULTS

Extensive axonal degeneration of the large heavily myelinated fibers was found in the brachial plexus from the patient with LHON. In LHON nerve fascicles, we counted over 10 times as many degenerated profiles as found in the control nerve fascicles.

CONCLUSIONS

Microscopic examination of the brachial plexus in the patient with LHON clearly demonstrated a significant pattern of neurodegeneration. Our study suggests that peripheral neuropathy may be a subclinical feature associated with LHON.

Auditory function in individuals within Leber's hereditary optic neuropathy pedigrees

The aims of this study are to investigate whether auditory dysfunction is part of the spectrum of neurological abnormalities associated with Leber's hereditary optic neuropathy (LHON) and to determine the perceptual consequences of auditory neuropathy (AN) in affected listeners. Forty-eight subjects confirmed by genetic testing as having one of four mitochondrial mutations associated with LHON (mt11778, mtDNA14484, mtDNA14482 and mtDNA3460) participated. Thirty-two of these had lost vision, and 16 were asymptomatic at the point of data collection. While the majority of individuals showed normal sound detection, >25% (of both symptomatic and asymptomatic participants) showed electrophysiological evidence of AN with either absent or severely delayed auditory brainstem potentials. Abnormalities were observed for each of the mutations, but subjects with the mtDNA11778 type were the most affected. Auditory perception was also abnormal in both symptomatic and asymptomatic subjects, with >20% of cases showing impaired detection of auditory temporal (timing) cues and >30% showing abnormal speech perception both in quiet and in the presence of background noise. The findings of this study indicate that a relatively high proportion of individuals with the LHON genetic profile may suffer functional hearing difficulties due to neural abnormality in the central auditory pathways.

Investigation of auditory dysfunction in Leber hereditary optic neuropathy

PURPOSE

To investigate the possibility of auditory dysfunction in patients with Leber hereditary optic neuropathy (LHON).

METHODS

We prospectively recruited 10 affected patients from the north-east of England harbouring one of the three primary mitochondrial LHON mutations (3460G>A n = 3, 11778G>A n = 5 and 14484T>C n = 2). A detailed auditory history was taken and they were asked to complete a validated hearing questionnaire. Each patient then underwent a comprehensive topographic neuroauditory assessment to evaluate both middle- and inner-ear functions and the integrity of the brainstem auditory pathways.

RESULTS

We found no evidence of cochlear nerve dysfunction or abnormalities of the central brainstem auditory pathways in our LHON cohort and five patients had completely normal hearing tests. The remainder had mild conductive hearing loss from childhood ear infections and/or high-frequency sensorineural hearing loss from previous noise injury.

CONCLUSION

Although further studies are required to confirm our findings, auditory dysfunction as a result of a primary LHON mutation is probably uncommon.

Leber's hereditary optic neuropathy triggered by antiretroviral therapy for human immunodeficiency virus

PURPOSE

To describe the clinical features of two cases of Leber's hereditary optic neuropathy (LHON) precipitated by antiretroviral treatment for human immunodeficiency virus (HIV) infection.

METHODS

Two cases of LHON (from an expected four new cases a year throughout Australia) were identified in men on treatment for HIV infection.

RESULTS

Two HIV-infected men were receiving combination antiretroviral therapy that included nucleoside analogues. Both patients carried the 14 484 mitochondrial DNA mutation and were distantly related (seventh cousins). Although both men presented with sequential visual loss typical of LHON and one had a known close relative affected by LHON, the correct diagnosis was delayed in both cases. The final visual outcome was profoundly reduced in both instances and cessation of antiretroviral therapy did not result in recovery of vision in one patient.

CONCLUSION

Patients with a family history of LHON who require antiretroviral treatment should be warned of the high risk of severe visual loss. The underlying mechanism of antiretroviral side effects may help characterize the other trigger factors for LHON.

Leigh-like encephalopathy complicating Leber's hereditary optic neuropathy

Leber's hereditary optic neuropathy is a mitochondrial disease caused by point mutations in mitochondrial DNA. It usually presents as severe bilateral visual loss in young adults. We report on a neurological disorder resembling Leigh syndrome, which complicated Leber's hereditary optic neuropathy in three unrelated male patients harboring mitochondrial DNA mutations at nucleotide positions 3460, 14459, and 14484, respectively. This Leigh-like encephalopathy appears to be associated with a much more severe outcome than isolated Leber's hereditary optic neuropathy.

Clinical, biochemical and molecular genetic features of Leber's hereditary optic neuropathy

Leber's hereditary optic neuropathy (LHON) has traditionally been considered a disease causing severe and permanent visual loss in young adult males. In nearly all families with LHON it is associated with one of three pathogenic mitochondrial DNA (mtDNA) mutations, at bp 11778, 3460 or 14484. The availability of mtDNA confirmation of a diagnosis of LHON has demonstrated that LHON occurs with a wider range of age at onset and more commonly in females than previously recognised. In addition, analysis of patients grouped according to mtDNA mutation has demonstrated differences both in the clinical features of visual failure and in recurrence risks to relatives associated with each of the pathogenic mtDNA mutations. Whilst pathogenic mtDNA mutations are required for the development of LHON, other factors must be reponsible for the variable penetrance and male predominance of this condition. Available data on a number of hypotheses including the role of an additional X-linked visual loss susceptibility locus, impaired mitochondrial respiratory chain activity, mtDNA heteroplasmy, environmental factors and autoimmunity are discussed. Subacute visual failure is seen in association with all three pathogenic LHON mutations. However, the clinical and experimental data reviewed suggest differences in the phenotype associated with each of the three mutations which may reflect variation in the disease mechanisms resulting in this common end-point.