Next-Generation Sequencing Identifies Novel PMPCA Variants in Patients with Late-Onset Dominant Optic Atrophy.

Dominant Optic Atrophy (DOA) is one of the most common inherited mitochondrial diseases, leading to blindness. It is caused by the chronic degeneration of the retinal ganglion cells (RGCs) and their axons forming the optic nerve. Until now, DOA has been mainly associated with genes encoding proteins involved in mitochondrial network dynamics. Using next-generation and exome sequencing, we identified for the first time heterozygous PMPCA variants having a causative role in the pathology of late-onset primary DOA in five patients. PMPCA encodes an α subunit of the mitochondrial peptidase (MPP), responsible for the cleavage and maturation of the mitochondrial precursor proteins imported from the cytoplasm into mitochondria. Recently, PMPCA has been identified as the gene responsible for Autosomal Recessive Cerebellar Ataxia type 2 (SCAR2) and another severe recessive mitochondrial disease. In this study, four PMPCA variants were identified, two are frameshifts (c.309delA and c.820delG) classified as pathogenic and two are missenses (c.1363G>A and c.1547G>A) classified with uncertain pathological significance. Functional assays on patients' fibroblasts show a hyperconnection of the mitochondrial network and revealed that frameshift variants reduced α-MPP levels, while not significantly affecting the respiratory machinery. These results suggest that alterations in mitochondrial peptidase function can affect the fusion-fission balance, a key element in maintaining the physiology of retinal ganglion cells, and consequently lead to their progressive degeneration.

Pathogenic NR2F1 variants cause a developmental ocular phenotype recapitulated in a mutant mouse model.

Pathogenic NR2F1 variants cause a rare autosomal dominant neurodevelopmental disorder referred to as the Bosch-Boonstra-Schaaf Optic Atrophy Syndrome. Although visual loss is a prominent feature seen in affected individuals, the molecular and cellular mechanisms contributing to visual impairment are still poorly characterized. We conducted a deep phenotyping study on a cohort of 22 individuals carrying pathogenic NR2F1 variants to document the neurodevelopmental and ophthalmological manifestations, in particular the structural and functional changes within the retina and the optic nerve, which have not been detailed previously. The visual impairment became apparent in early childhood with small and/or tilted hypoplastic optic nerves observed in 10 cases. High-resolution optical coherence tomography imaging confirmed significant loss of retinal ganglion cells with thinning of the ganglion cell layer, consistent with electrophysiological evidence of retinal ganglion cells dysfunction. Interestingly, for those individuals with available longitudinal ophthalmological data, there was no significant deterioration in visual function during the period of follow-up. Diffusion tensor imaging tractography studies showed defective connections and disorganization of the extracortical visual pathways. To further investigate how pathogenic NR2F1 variants impact on retinal and optic nerve development, we took advantage of an Nr2f1 mutant mouse disease model. Abnormal retinogenesis in early stages of development was observed in Nr2f1 mutant mice with decreased retinal ganglion cell density and disruption of retinal ganglion cell axonal guidance from the neural retina into the optic stalk, accounting for the development of optic nerve hypoplasia. The mutant mice showed significantly reduced visual acuity based on electrophysiological parameters with marked conduction delay and decreased amplitude of the recordings in the superficial layers of the visual cortex. The clinical observations in our study cohort, supported by the mouse data, suggest an early neurodevelopmental origin for the retinal and optic nerve head defects caused by NR2F1 pathogenic variants, resulting in congenital vision loss that seems to be non-progressive. We propose NR2F1 as a major gene that orchestrates early retinal and optic nerve head development, playing a key role in the maturation of the visual system.

Pourfour du Petit Syndrome: A Rare Association With Cluster Headache.

Pourfour du Petit syndrome is an uncommon cause of eyelid retraction, associated with unilateral mydriasis and hemifacial hyperhidrosis. This syndrome is caused by hyperactivity of the ipsilateral oculosympathetic pathway and needs to be recognized because it has an opposite clinical presentation but the same topographic and diagnostic value as Horner syndrome. The authors report a rare case of Pourfour du Petit syndrome associated with cluster headache and discuss pathophysiological hypotheses, clinical presentation, complementary exams, pharmacologic testing, treatment options, and prognosis. Early detection of these symptoms may lead to swift diagnosis and treatment.

Orthoptic and video-oculographic analyses in oculopharyngeal muscular dystrophy.

INTRODUCTION: Mild ophthalmoparesis can be seen in oculopharyngeal muscular dystrophy (OPMD). METHODS: Orthoptic analysis included assessment of phoria/tropia, eye excursion, saccades, pursuit, stereoacuity, and Hess-Lancaster screen test. Video-oculography included fixation, horizontal and vertical saccades, and pursuit. RESULTS: Orthoptic abnormalities were: tropia (4 of 6); abnormal eye excursion (4 of 6, 78% involved lateral or superior rectus muscles); abnormal horizontal or vertical saccades (2 of 6); abnormal pursuit (0 of 6); abnormal stereoacuity (2 of 6); and pathological Hess-Lancaster screen (4 of 6). Video-oculographic abnormalities were present for: fixation (1 of 6); saccade latency (1 of 6); horizontal pursuit (3 of 6); and vertical pursuit (0 of 6). For horizontal saccades, mean velocity, peak velocity, and gain were pathological in 5 of 6, 5 of 6 (61% of pathological mean and peak velocities involved abducting eye movements), and 3 of 6, respectively. For vertical saccades, mean velocity, peak velocity, and gain were pathological in 4 of 6, 4 of 6 (53% involved upward movements), and 3 of 6, respectively. CONCLUSION: The data indicate preferential involvement of lateral and (to a lesser degree) superior rectus muscles in OPMD.

Warmer weather linked to tick attack and emergence of severe rickettsioses.

The impact of climate on the vector behaviour of the worldwide dog tick Rhipicephalus sanguineus is a cause of concern. This tick is a vector for life-threatening organisms including Rickettsia rickettsii, the agent of Rocky Mountain spotted fever, R. conorii, the agent of Mediterranean spotted fever, and the ubiquitous emerging pathogen R. massiliae. A focus of spotted fever was investigated in France in May 2007. Blood and tissue samples from two patients were tested. An entomological survey was organised with the study of climatic conditions. An experimental model was designed to test the affinity of Rh. sanguineus for biting humans in variable temperature conditions. Serological and/or molecular tools confirmed that one patient was infected by R. conorii, whereas the other was infected by R. massiliae. Dense populations of Rh. sanguineus were found. They were infected with new genotypes of clonal populations of either R. conorii (24/133; 18%) or R. massiliae (13/133; 10%). April 2007 was the warmest since 1950, with summer-like temperatures. We show herein that the human affinity of Rh. sanguineus was increased in warmer temperatures. In addition to the originality of theses cases (ophthalmic involvements, the second reported case of R. massiliae infection), we provide evidence that this cluster of cases was related to a warming-mediated increase in the aggressiveness of Rh. sanguineus, leading to increased human attacks. From a global perspective, we predict that as a result of globalisation and warming, more pathogens transmitted by the brown dog tick may emerge in the future.

Optical coherence tomography in neuromyelitis optica.

BACKGROUND: Neuromyelitis optica (NMO) is an inflammatory disease with combined features of optic neuritis and myelitis. This pathologic entity may induce severe disability, including visual loss and paraplegia. Other than clinical follow-up, there is no marker for severity of the disease. OBJECTIVES: To evaluate the use of optical coherence tomography (OCT) in NMO and to determine whether this new technique could be a good marker of axonal loss in NMO. DESIGN: Cross-sectional study. PARTICIPANTS: Thirty-five patients with NMO or at a high risk for NMO (having optic neuritis or myelitis and who are positive for NMO antibody) were prospectively studied. Fifteen healthy individuals served as control subjects. MAIN OUTCOME MEASURE: All patients underwent a complete ophthalmologic evaluation, including OCT, funduscopy, and visual field, visual acuity, and visual evoked potential testing. Expanded Disability Status Scale scores were assessed but without the visual data. Correlations between the visual test results and demographic or clinical characteristics were evaluated. RESULTS: Optical coherence tomography and visual field data were available for only 32 patients because 3 patients were blind. The mean retinal nerve fiber layer thickness was significantly reduced in patients with NMO compared with controls (P < .001). We found good correlation between the OCT results and visual field testing. We also found weak correlation between OCT results and both visual acuity and visual evoked potential latencies. We did not find any correlation between OCT results and age, sex, or disease duration. In contrast, retinal nerve fiber layer thickness was closely correlated with the Expanded Disability Status Scale score (P < .001). CONCLUSIONS: Optical coherence tomography results are significantly altered in patients with NMO. Optical coherence tomography is easy to perform, and the results are well correlated with visual acuity and visual field findings. It could be considered a marker of axonal loss because we found good correlation between OCT and the Expanded Disability Status Scale score. These preliminary results will need to be confirmed in a longitudinal prospective study.