Posted in Journal Reviews on 11th Dec 2012
Data that emanate from Genome Wide Association Studies (GWAS) are often at first difficult to construe. New findings are reported on a weekly basis, providing potential, but as yet unclear, insights into the pathogenesis of hitherto poorly understood common clinical disorders. It is worth noting here the significant advances made in areas of clinical neurology on the back of such studies. Nevertheless, identifying an association represents the very beginning of a quest to understand disease at the molecular level.
Restless legs syndrome (RLS) is said to affect up to 10% of the population, 60% of which report a family history. Previous GWAS have identified a number of candidate genes that appear to be associated with RLS. This short list includes a SNP (Single Nucleotide Polymorphism) linked to the BTBD9 gene that appears to account for approximately 50% of the population-attributable risk. How BTBD9 and RLS are linked is the focus of a recently published report by Freeman et al. in the Current Biology.
Freeman et al. used the fruit fly, Drosophila, as the model organisms to investigate the function of the fly homologue of BTBD9 (dBTBD9). They found that the protein product is widely expressed in Drosophila brains and appears to have a discrete punctate localisation within neurones. Remarkably, Drosophila mutants lacking dBTBD9 displayed fragmented night-time sleep similar to human patients which could be rescued by introducing the wild-type gene. Moreover, the authors found that when the flies were enclosed in a confined space, they became hyperlocomotive, analogous to the ‘restlessness’ seen in RLS patients. Importantly, Freeman et al. did not observe any defect in general locomotion suggesting a motor deficit.
Patients with RLS are treated with Dopaminergic drugs, suggesting an underlying defect in dopamine signalling in patient brains. Indeed, Freeman et al. did find a 50% reduction in total dopamine in the mutant flies, and when treated with Pramipexole, the previously-seen sleep abnormalities improved to control levels. In addition, defects in iron metabolism have also been reported in RLS patients and Freeman et al. also describe data showing links between BTBD9 and ferritin expression in cell culture.
This work therefore not only provides corroborating evidence that the GWAS findings from patients with RLS appear significant but also illustrates the potential power of ongoing genetic screening in tandem with laboratory research to understand neural function. However, many outstanding questions remain including how does BTBD9 regulate sleep and locomotion at the molecular level and, crucially, how does the identified SNP predispose to clinical disease? The answers can only be provided by further laboratory studies. – Rhys Roberts, Cambridge Institute for Medical Research and Addenbrooke’s Hospital, Cambridge.
Freeman A, Pranski E, Miller RD, Radmard S, Bernhard D, Jinnah HA, Betarbet R Rye DB and Sanyal S. Sleep Fragmentation and Motor Restlessness in a Drosophila Model of Restless Legs Syndrome. Current Biology 2012;22:1142-8.
Pushed aside and cross-linked cleanly
Laurent Groc in Bordeaux studies the surface interactions and kinetics of the NMDA receptor and other proteins. Mikasova and others in his group show, with cell culture and animal work, nicely done single particle trafficking photographs and studies of long term potentiation (LTP), that NMDAR antibodies from the serum and cerebrospinal fluid of patients with NMDAR encephalitis rapidly disperse synaptic NR2A containing NMDA receptors on the cell surface and cross-link and internalise extra-synaptic NR2B containing receptors. Synaptic plasticity is impaired with inability to upregulate AMPA receptors via LTP. The effects are seen within minutes of application of the antibodies to hippocampal neuronal cells in culture. Activation of the Ephrin-B2 receptor in vitro and in vivo can rescue these effects, which provides a pathway that may translate to an effective adjunct therapy for patients. Christian Bien and Jan Bauer with international collaborators provide a detailed neuropathological comparative study of the old intracellular-antigen (e.g. Hu) associated encephalitides, with evidence of predominantly CD8 T-cell associated inflammation, in comparison to ‘cell-surface’-encephalitides including potassium channel complex antibody associated encephalopathy and NMDAR encephalitis. 17 patients’ samples are examined, 6 with post mortem analyses. Potassium channel antibody cases (including one confirmed Lgi-1 antibody case) are associated with complement deposition and less cellular infiltrate, but NMDAR encephalitis cases (albeit with a small sample of 3 cases with neocortical biopsy samples only) have barely any evidence of neuronal loss, inflammation or complement activation. This work replicates other previous studies of the neuropathology of NMDAR encephalitis, and supports the prevailing hypothesis that NMDAR antibodies are genuinely pathogenic in themselves. There is a case for renaming NMDAR encephalitis as NMDAR antibody associated encephalopathy. – Mike Zandi, Addenbrooke’s Hospital, Cambridge.
Disrupted surface cross-talk between NMDA and Ephrin-B2 receptors in anti-NMDA encephalitis. Mikasova et al. BRAIN 2012:135(5);1606–21.
Immunopathology of autoantibody-associated encephalitides: clues for pathogenesis. Bien et al. BRAIN 2012:135(5):1622-38.
Lawrence and Kuypers films
Twenty films are now made freely available, for the first time, on the Brain website to accompany two classic papers of Don Lawrence and Hans Kuypers from 1968. The pair examined motor control (and recovery) after lesions to the corticospinal system (bilateral pyramidotomy), ventromedial descending brainstem pathways (posture and balance) and the lateral brainstem pathways (reach and grasp) in the Old World macaque monkey. The 16mm films were made in Cleveland between 1963 and 1966, and inspired many studies of motor plasticity. – Mike Zandi, National Hospital for Neurology and Neurosurgery, Queen Square, London.
Lawrence and Kuypers (1968a, b) revisited: copies of the original filmed material from their classic papers in Brain. Lemon et al. BRAIN 2012:135(7):2290-5.
Lawrence DG, Kuypers HGJM. The functional organisation of the motor system in the monkey. I. The effects of bilateral pyramidal lesions. BRAIN 1968a;91:1–14.
Lawrence DG, Kuypers HGJM. The functional organisation of the motor system in the monkey. II. The effects of lesions of the descending brain-stem pathways. BRAIN 1968b;91:15–36.
Mere therapies (and mouse telemetry)
These two papers provide animal model evidence for the use of micro RNAs in the treatment of neurological disease. The first, from Nagoya, tackled Kennedy’s spinal and bulbar muscular atrophy (SBMA) due to the polyglutamine expansion in the androgen receptor. MiR-196a is a micro RNA which, when given with a viral vector, silences a stabiliser of androgen receptor mRNA, CELF2 (CUGBP, Elav-like family member 2), lessening the phenotype in SBMA mice and reducing expression of the androgen receptor mRNA in fibroblasts from patients with the disease. The second paper, from Dublin, looked at the use of Mir-134, a micro RNA known to be important in the activity-regulation of dendritic spine structure and remodelling, in epilepsy. The authors demonstrate upregulation of Mir-134 in kainic acid induced status epilepticus in BL/6 mice, and found higher levels of Mir-134 in the resected temporal lobes of patients with refractory temporal lobe epilepsy compared to non-neurological controls. The authors then carried out EEG telemetry for 2 weeks on mice, comparing a group with MiR-134 silencing and those without, demonstrating marked reduction in evoked seizures in the MiR-134 silenced group. – Mike Zandi, Addenbrooke’s Hospital, Cambridge.
Viral delivery of miR-196a ameliorates the SBMA phenotype via the silencing of CELF2. Miyazaki et al. NATURE MEDICINE. Published online 3 June 2012.
Silencing microRNA-134 produces neuroprotective and prolonged seizure-suppressive effects. Jimenez-Mateos et al. NATURE MEDICINE. Published online 10 June 2012.