Identification of genetic variants associated with Huntington's disease progression: a genome-wide association study

Background Huntington's disease is caused by a CAG repeat expansion in the huntingtin gene, HTT. Age at onset has been used as a quantitative phenotype in genetic analysis looking for Huntington's disease modifiers, but is hard to define and not always available. Therefore, we aimed to generate a novel measure of disease progression and to identify genetic markers associated with this progression measure. Methods We generated a progression score on the basis of principal component analysis of prospectively acquired longitudinal changes in motor, cognitive, and imaging measures in the 218 indivduals in the TRACK-HD cohort of Huntington's disease gene mutation carriers (data collected 2008–11). We generated a parallel progression score using data from 1773 previously genotyped participants from the European Huntington's Disease Network REGISTRY study of Huntington's disease mutation carriers (data collected 2003–13). We did a genome-wide association analyses in terms of progression for 216 TRACK-HD participants and 1773 REGISTRY participants, then a meta-analysis of these results was undertaken. Findings Longitudinal motor, cognitive, and imaging scores were correlated with each other in TRACK-HD participants, justifying use of a single, cross-domain measure of disease progression in both studies. The TRACK-HD and REGISTRY progression measures were correlated with each other (r=0·674), and with age at onset (TRACK-HD, r=0·315; REGISTRY, r=0·234). The meta-analysis of progression in TRACK-HD and REGISTRY gave a genome-wide significant signal (p=1·12 × 10−10) on chromosome 5 spanning three genes: MSH3, DHFR, and MTRNR2L2. The genes in this locus were associated with progression in TRACK-HD (MSH3 p=2·94 × 10−8 DHFR p=8·37 × 10−7 MTRNR2L2 p=2·15 × 10−9) and to a lesser extent in REGISTRY (MSH3 p=9·36 × 10−4 DHFR p=8·45 × 10−4 MTRNR2L2 p=1·20 × 10−3). The lead single nucleotide polymorphism (SNP) in TRACK-HD (rs557874766) was genome-wide significant in the meta-analysis (p=1·58 × 10−8), and encodes an aminoacid change (Pro67Ala) in MSH3. In TRACK-HD, each copy of the minor allele at this SNP was associated with a 0·4 units per year (95% CI 0·16–0·66) reduction in the rate of change of the Unified Huntington's Disease Rating Scale (UHDRS) Total Motor Score, and a reduction of 0·12 units per year (95% CI 0·06–0·18) in the rate of change of UHDRS Total Functional Capacity score. These associations remained significant after adjusting for age of onset. Interpretation The multidomain progression measure in TRACK-HD was associated with a functional variant that was genome-wide significant in our meta-analysis. The association in only 216 participants implies that the progression measure is a sensitive reflection of disease burden, that the effect size at this locus is large, or both. Knockout of Msh3 reduces somatic expansion in Huntington's disease mouse models, suggesting this mechanism as an area for future therapeutic investigation

Microdialysis Assessment of Cerebral Perfusion during Cardiac Arrest, Extracorporeal Life Support and Cardiopulmonary Resuscitation in Rats – A Pilot Trial

<div><p>Cerebral metabolic alterations during cardiac arrest, cardiopulmonary resuscitation (CPR) and extracorporeal cardiopulmonary life support (ECLS) are poorly explored. Markers are needed for a more personalized resuscitation and post—resuscitation care. Aim of this study was to investigate early metabolic changes in the hippocampal CA1 region during ventricular fibrillation cardiac arrest (VF-CA) and ECLS versus conventional CPR. Male Sprague-Dawley rats (350g) underwent 8min untreated VF-CA followed by ECLS (n = 8; bloodflow 100ml/kg), mechanical CPR (n = 18; 200/min) until return of spontaneous circulation (ROSC). Shams (n = 2) were included. Glucose, glutamate and lactate/pyruvate ratio were compared between treatment groups and animals with and without ROSC. Ten animals (39%) achieved ROSC (ECLS 5/8 vs. CPR 5/18; OR 4,3;CI:0.7–25;p = 0.189). During VF-CA central nervous glucose decreased (0.32±0.1mmol/l to 0.04±0.01mmol/l; p<0.001) and showed a significant rise (0.53±0.1;p<0.001) after resuscitation. Lactate/pyruvate (L/P) ratio showed a 5fold increase (31 to 164; p<0.001; maximum 8min post ROSC). Glutamate showed a 3.5-fold increase to (2.06±1.5 to 7.12±5.1μmol/L; p<0.001) after CA. All parameters normalized after ROSC with no significant differences between ECLS and CPR. Metabolic changes during ischemia and resuscitation can be displayed by cerebral microdialysis in our VF-CA CPR and ECLS rat model. We found similar microdialysate concentrations and patterns of normalization in both resuscitation methods used.</p><p><b><i>Institutional Protocol Number</i>:</b> GZ0064.11/3b/2011</p></div

CA1 lactate/pyruvate ratio against time.

<p>x-axis: Point of measurement, measurements 8min apart (sampling interval of 8min); y axis: Lactate/pyruvate ratios (mean values and standard deviation); CA, cardiac arrest; CPR, cardiopulmonary resuscitation; ECLS, extracorporeal cardiopulmonary life support; BL, baseline; ROSC, return of spontaneous circulation.</p

CA1 glucose mmol/l against time.

<p>x-axis: Point of measurement, measurements 8min apart (sampling interval of 8min); y axis: Glucose (mmol/l; mean values and standard deviation); CA, cardiac arrest; CPR, cardiopulmonary resuscitation; ECLS, extracorporeal cardiopulmonary life support; BL, baseline; ROSC, return of spontaneous circulation.</p

Mean arterial blood pressure in mm Mercury against time.

<p>X-axis: time in minutes; Y-axis: mean arterial blood pressure invasively measured in mmHg (mean with standard deviation); VFCA, ventricular fibrillation cardiac arrest; ROSC, return of spontaneous circulation; ECLS, extracorporeal life support; CPR, cardiopulmonary resuscitation; The p value displayed results from comparison of mean values the interval of measurements min 70 to 74.</p

Representative pictures of cerebral cortex, hippocampal CA1 region and thalamic reticular nucleus.

<p>A-C: Cerebral cortex without lesions in sham (A), CPR (B) and ECLS (C) animals; H&E staining, bar = 40μm; D-F: Hippocampal CA1 region without lesions in sham (D), CPR (E) and ECLS (F) animals; H&E staining, bar = 40μm; G-I: Thalamic reticular nucleus, no lesions in sham animal (G), numerous shrunken neurons with condensation of nuclear chromatin in CPR (H) and ECLS (I) animals; H&E staining, bar = 40μm; inserts show close-up views of one neuron in the respective animal; H&E staining, bar = 10μm.</p

Timeline of the experiment.

<p>Microdiyalsis sampling interval conituously with 1 sample over 8min; Time scale is non linear to allow better overview; VF, ventricular fibrillation; ROSC, return of spontaneous circulation; CPR, cardiopulmonary resuscitation; ECLS, extracorporeal cardiopulmonary life support.</p

CA1 glutamate μmol/l against time.

<p>x-axis: Point of measurement, measurements 8min apart (sampling interval of 8min); y axis: Glutamate (μmol/l; mean values and standard deviation); CA, cardiac arrest; CPR, cardiopulmonary resuscitation; ECLS, extracorporeal cardiopulmonary life support; BL, baseline; ROSC, return of spontaneous circulation.</p