Quantum Rings in Electromagnetic Fields

This is the author accepted manuscript. The final version is available from Springer via the DOI in this recordThis chapter is devoted to optical properties of so-called Aharonov-Bohm quantum rings (quantum rings pierced by a magnetic flux resulting in AharonovBohm oscillations of their electronic spectra) in external electromagnetic fields. It studies two problems. The first problem deals with a single-electron AharonovBohm quantum ring pierced by a magnetic flux and subjected to an in-plane (lateral) electric field. We predict magneto-oscillations of the ring electric dipole moment. These oscillations are accompanied by periodic changes in the selection rules for inter-level optical transitions in the ring allowing control of polarization properties of the associated terahertz radiation. The second problem treats a single-mode microcavity with an embedded Aharonov-Bohm quantum ring which is pierced by a magnetic flux and subjected to a lateral electric field. We show that external electric and magnetic fields provide additional means of control of the emission spectrum of the system. In particular, when the magnetic flux through the quantum ring is equal to a half-integer number of the magnetic flux quanta, a small change in the lateral electric field allows for tuning of the energy levels of the quantum ring into resonance with the microcavity mode, thus providing an efficient way to control the quantum ring-microcavity coupling strength. Emission spectra of the system are discussed for several combinations of the applied magnetic and electric fields

A homozygous MED11 C-terminal variant causes a lethal neurodegenerative disease

Purpose: The mediator (MED) multisubunit-complex modulates the activity of the transcriptional machinery, and genetic defects in different MED subunits (17, 20, 27) have been implicated in neurologic diseases. In this study, we identified a recurrent homozygous variant in MED11 (c.325C>T; p.Arg109Ter) in 7 affected individuals from 5 unrelated families. Methods: To investigate the genetic cause of the disease, exome or genome sequencing were performed in 5 unrelated families identified via different research networks and Matchmaker Exchange. Deep clinical and brain imaging evaluations were performed by clinical pediatric neurologists and neuroradiologists. The functional effect of the candidate variant on both MED11 RNA and protein was assessed using reverse transcriptase polymerase chain reaction and western blotting using fibroblast cell lines derived from 1 affected individual and controls and through computational approaches. Knockouts in zebrafish were generated using clustered regularly interspaced short palindromic repeats/Cas9. Results: The disease was characterized by microcephaly, profound neurodevelopmental impairment, exaggerated startle response, myoclonic seizures, progressive widespread neurodegeneration, and premature death. Functional studies on patient-derived fibroblasts did not show a loss of protein function but rather disruption of the C-terminal of MED11, likely impairing binding to other MED subunits. A zebrafish knockout model recapitulates key clinical phenotypes. Conclusion: Loss of the C-terminal of MED subunit 11 may affect its binding efficiency to other MED subunits, thus implicating the MED-complex stability in brain development and neurodegeneration

Pelizaeus-Merzbacher disease: electrophysiological study of two sibs with the classic form and of their relatives.

We examined two sibs with the classic form of Pelizaeus-Merzbacher disease (PMD) and their relatives. Electromygraphic-electroneurographic studies and magnetic stimulation of motor pathways were performed. In both patients We found an absence of compound motor action potential (cMAP) after stimulation of the motor cortex and a normal conduction time by stimulating the cervical roots. Despite reported sparing of the peripheral nervous system in PMD, our conduction study of the tibial nerve revealed a slightly decreased motor nerve conduction velocity in one patient. In both patients the EMG study showed neurogenic findings. The elder sister showed a prolonged central motor conduction time. This study demonstrates abnormalities of motor corticospinal pathways also in PMD relatives suggesting that magnetic stimulation could be useful in detecting "subclinical" abnormalities in this dysmyelinating condition. Furthermore, in accordance with previous studies, we suggest that a slight involvement of the peripheral nervous system could be observed in PMD

Bickerstaff Brainstem Encephalitis and overlapping Guillain-Barre syndrome in children: Report of two cases and review of the literature

Bickerstaff Brainstem Encephalitis (BBE) is a rare autoimmune encephalitis, characterized by acute ophthalmoplegia, ataxia and altered state of consciousness. Together with Guillan-Barre Syndrome (GBS) and Miller-Fisher Syndrome, it forms a spectrum of post-infectious demyelinating diseases. Overlapping forms between BBE and GBS (BBE/GBS) are described in patients with lower limbs weakness and typical signs of BBE, suggesting a combined involvement of Central and Peripheral Nervous System (PNS), but only few reported cases are focused on pediatric population. We reviewed all cases of pediatric BBE in the literature, to determine if any patient showed features suggestive for BBE/GBS. Data analysis focused on the diagnostic tests performed (e.g. anti-GQ1b antibodies), neuroimaging and nerve conduction studies (NCS). Further attention was given to the therapeutic management and to patients' outcome. We additionally present two previously unreported pediatric cases. Our review retrieved 19 cases of BBE/GBS, only 2 of which were originally and correctly diagnosed by the authors. The prevalence was higher in male subjects (ratio 3:1) and median age at diagnosis was 8 years. Anti-GQ1b were positive in 46% of the patients, while NCS were altered in 64%. Only 25% of the patients that underwent brain MRI showed abnormal findings. The incidence of BBE/GBS has been underrated in the past, mostly due to an underestimation of the PNS involvement. We therefore suggest to investigate all patients with a clinical picture suggestive of BBE/GBS through electroencephalogram, NCS, brain and spine MRI in order to promptly achieve the correct diagnosis. (C) 2018 European Paediatric Neurology Society. Published by Elsevier Ltd. All rights reserved