Mutations in OPA1, a dynamin-related GTPase involved in mitochondrial fusion, cristae organization and control of apoptosis, have been linked to non-syndromic optic neuropathy transmitted as an autosomal-dominant trait (DOA). We here report on eight patients from six independent families showing that mutations in the OPA1 gene can also be responsible for a syndromic form of DOA associated with sensorineural deafness, ataxia, axonal sensory-motor polyneuropathy, chronic progressive external ophthalmoplegia and mitochondrial myopathy with cytochrome c oxidase negative and Ragged Red Fibres. Most remarkably, we demonstrate that these patients all harboured multiple deletions of mitochondrial DNA (mtDNA) in their skeletal muscle, thus revealing an unrecognized role of the OPA1 protein in mtDNA stability. The five OPA1 mutations associated with these DOA ‘plus’ phenotypes were all mis-sense point mutations affecting highly conserved amino acid positions and the nuclear genes previously known to induce mtDNA multiple deletions such as POLG1, PEO1 (Twinkle) and SLC25A4 (ANT1) were ruled out. Our results show that certain OPA1 mutations exert a dominant negative effect responsible for multi-systemic disease, closely related to classical mitochondrial cytopathies, by a mechanism involving mtDNA instability.

Objective: Melanopsin retinal ganglion cells (mRGCs) are photoreceptors driving circadian photoentrainment, and circadian dysfunction characterizes Alzheimer disease (AD). We investigated mRGCs in AD, hypothesizing that they contribute to circadian dysfunction.Methods: We assessed retinal nerve fiber layer (RNFL) thickness by optical coherence tomography (OCT) in 21 mild‐moderate AD patients, and in a subgroup of 16 we evaluated rest–activity circadian rhythm by actigraphy. We studied postmortem mRGCs by immunohistochemistry in retinas, and axons in optic nerve cross‐sections of 14 neuropathologically confirmed AD patients. We coimmunostained for retinal amyloid β (Aβ) deposition and melanopsin to locate mRGCs. All AD cohorts were compared with age‐matched controls.Results: We demonstrated an age‐related optic neuropathy in AD by OCT, with a significant reduction of RNFL thickness (p = 0.038), more evident in the superior quadrant (p = 0.006). Axonal loss was confirmed in postmortem AD optic nerves. Abnormal circadian function characterized only a subgroup of AD patients. Sleep efficiency was significantly reduced in AD patients (p = 0.001). We also found a significant loss of mRGCs in postmortem AD retinal specimens (p = 0.003) across all ages and abnormal mRGC dendritic morphology and size (p = 0.003). In flat‐mounted AD retinas, Aβ accumulation was remarkably evident inside and around mRGCs.Interpretation: We show variable degrees of rest–activity circadian dysfunction in AD patients. We also demonstrate age‐related loss of optic nerve axons and specifically mRGC loss and pathology in postmortem AD retinal specimens, associated with Aβ deposition. These results all support the concept that mRGC degeneration is a contributor to circadian rhythm dysfunction in AD. ANN NEUROL 2016;79:90–109

Morvan's ‘fibrillary chorea’ or Morvan's syndrome is characterized by neuromyotonia (NMT), pain, hyperhydrosis, weight loss, severe insomnia and hallucinations. We describe a man aged 76 years with NMT, dysautonomia, cardiac arrhythmia, lack of slow-wave sleep and abnormal rapid eye movement sleep. He had raised serum antibodies to voltage-gated K⁺ channels (VGKC), oligoclonal bands in his CSF, markedly increased serum norepinephrine, increased serum cortisol and reduced levels and absent circadian rhythms of prolactin and melatonin. The neurohormonal findings and many of the clinical features were very similar to those in fatal familial insomnia, a hereditary prion disease that is associated with thalamic degenerative changes. Strikingly, however, all symptoms in our MFC patient improved with plasma exchange. The patient died unexpectedly 11 months later. At autopsy, there was a pulmonary adenocarcinoma, but brain pathology showed only a microinfarct in the hippocampus and no thalamic changes. The NMT and some of the autonomic features are likely to be directly related to the VGKC antibodies acting in the periphery. The central symptoms might also be due to the direct effects of VGKC antibodies, or perhaps of other autoantibodies still to be defined, on the limbic system with secondary effects on neurohormone levels. Alternatively, changes in secretion of neurohormones in the periphery might contribute to the central disturbance. The relationship between VGKC antibodies, neurohormonal levels, autonomic, limbic and sleep disorders requires further study.

Leber’s hereditary optic neuropathy is a maternally inherited blinding disease caused as a result of homoplasmic point mutations in complex I subunit genes of mitochondrial DNA. It is characterized by incomplete penetrance, as only some mutation carriers become affected. Thus, the mitochondrial DNA mutation is necessary but not sufficient to cause optic neuropathy. Environmental triggers and genetic modifying factors have been considered to explain its variable penetrance. We measured the mitochondrial DNA copy number and mitochondrial mass indicators in blood cells from affected and carrier individuals, screening three large pedigrees and 39 independently collected smaller families with Leber’s hereditary optic neuropathy, as well as muscle biopsies and cells isolated by laser capturing from post-mortem specimens of retina and optic nerves, the latter being the disease targets. We show that unaffected mutation carriers have a significantly higher mitochondrial DNA copy number and mitochondrial mass compared with their affected relatives and control individuals. Comparative studies of fibroblasts from affected, carriers and controls, under different paradigms of metabolic demand, show that carriers display the highest capacity for activating mitochondrial biogenesis. Therefore we postulate that the increased mitochondrial biogenesis in carriers may overcome some of the pathogenic effect of mitochondrial DNA mutations. Screening of a few selected genetic variants in candidate genes involved in mitochondrial biogenesis failed to reveal any significant association. Our study provides a valuable mechanism to explain variability of penetrance in Leber’s hereditary optic neuropathy and clues for high throughput genetic screening to identify the nuclear modifying gene(s), opening an avenue to develop predictive genetic tests on disease risk and therapeutic strategies.

Objective: To investigate (1) whether phosphorylated α-synuclein deposits in skin nerve fibers might represent a useful biomarker for idiopathic Parkinson disease (IPD), and (2) the underlying pathogenesis of peripheral neuropathy associated with IPD. Methods: Twenty-one well-characterized patients with IPD were studied together with 20 patients with parkinsonisms assumed not to have α-synuclein deposits (PAR; 10 patients fulfilling clinical criteria for vascular parkinsonism, 6 for tauopathies, and 4 with parkin mutations) and 30 controls. Subjects underwent nerve conduction velocities from the leg to evaluate large nerve fibers and skin biopsy from proximal (i.e., cervical) and distal (i.e., thigh and distal leg) sites to study small nerve fibers and deposits of phosphorylated α-synuclein considered the pathologic form of α-synuclein. Results: Patients with IPD showed a small nerve fiber neuropathy prevalent in the leg with preserved large nerve fibers. PAR patients showed normal large and small nerve fibers. Phosphorylated α-synuclein was not found in any skin sample in PAR patients and controls, but it was found in all patients with IPD in the cervical skin site. Abnormal deposits were correlated with leg epidermal denervation. Conclusions: The search for phosphorylated α-synuclein in proximal peripheral nerves is a sensitive biomarker for IPD diagnosis, helping to differentiate IPD from other parkinsonisms. Neuritic inclusions of α-synuclein were correlated with a small-fiber neuropathy, suggesting their direct role in peripheral nerve fiber damage. Classification of evidence: This study provides Class III evidence that the presence of phosphorylated α-synuclein in skin nerve fibers on skin biopsy accurately distinguishes IPD from other forms of parkinsonism.