Introduction

Huntington disease (HD) is an autosomal dominant neurodegenerative disorder characterised by motor disturbances, cognitive decline, and neuropsychiatric symptoms. It is caused by a CAG repeat expansion (>36 repeats) in exon 1 of the HTT gene. [1] The lengths of the expanded CAG tract is inversely related to the age at clinical onset of HD, accounting for more than half of the overall variance in age at onset (AO). [2] Despite this strong correlation, there remains considerable variation of over 40 years in AO in individuals with identical repeat lengths. Several candidate modifier genes of HD have already been described in independent studies. [3] [4] [5] [6] [7] [8] [9] In order to confirm the associations between modifier gene variations and AO, independent replication studies are compulsory. Here, we tested the primary hypothesis of an original study [4] , that variations in the NR2A and NR2B glutamate receptor subunit genes ( GRIN2A , GRIN2B ) explain additional variance in AO for HD.

Methods

The study cohort comprised 1,211 individuals of European ancestry with HD collected by the EHDN “REGISTRY” study prior to October 14, 2008. “REGISTRY” is a multi-centre, multi-national observational study which aims to obtain natural history data on a wide spectrum of the European HD population (https://www.euro-hd.net/html/registry). [10] In order to test previously reported HD genetic modifiers in this cohort, HD patients with available data on age, sex, age at symptom onset, mutant CAG repeat size and body mass index (BMI) were included (initial n = 1211; n = 1069; 529 men and 540 women had a complete data set).

The expanded trinucleotide repeats ranged from 40 to 89 with a mean (± SD) of 45±4.7 CAGs, and AO ranged from 6 to 74 years, with an onset (mean ± SD) of 42 ±11.8 years. AO was defined as the age at which, according to the rater, the first signs of HD appeared. Five hundred and thirty-eight patients first presented with motor disturbances (mean ± SD motor AO = 43.4±11.6 years), 241 with psychiatric problems (mean ± SD psychiatric AO = 39.9±10.8 years), and 112 with cognitive decline (mean ± SD cognitive AO = 38.6±13.1 years). For the remaining patients no specific symptoms were listed (mean ± SD AO = 42.1±11.8 years). Genotyping of three SNPs was conducted as described before. [4]

Results

None of the SNPs deviated from Hardy – Weinberg Equilibrium (HWE). Considering the earliest AO ( n = 1,069), we did find evidence of association of the GRIN2A SNP rs2650427 (table 1). The R 2 statistic rose modestly (from 0.634 to 0.635) but significantly (p=0.028) when GRIN2A genotypes were added to the regression model. The analysis did not, however, replicate the association reported between the SNP rs1969060 in intron 2 of the GRIN2A gene and SNP C2664T (rs1806201) in exon 12 of the GRIN2B gene (table 1); but when dividing the cohort according to the nature of the symptoms presented initially, both the GRIN2B C2664T and the GRIN2A rs1969060 polymorphisms explained a small but considerable amount of additional variance in residual AO in the respective samples. Inclusion of the GRIN2B genotypes in the model for motor AO ( n = 538) increased the R 2 statistic from 0.620 to 0.623 (p=0.046) and in the study of 241 patients with psychiatric AO, the R 2 statistic of the exponential regression rose from 0.515 to 0.523 with the GRIN2A rs1969060 genotypes included (p=0.026, table 1). Interestingly, the association of cognitive AO ( n = 112) with the GRIN2A rs2650427 polymorphism shows the highest nominal significance as compared to the other models in the study (0.770 to 0.775, p=0.014). Yet, the results remain statisticallysignificant when excluding the patients with CAGs over >70 (n=4).

Model Genotypes CAGmean ± SD erliest AO
mean ± SD		 R²* P value
HD CAG 40-89 ( n =1069) 44.97±4.7 41.87±11.8 0.634 <0.0005
+ GRIN2B C2664T (rs1806201) CC (n=560) 44.94±4.8 42.13±12.1 0.634 0.541
CT (n=436) 45.02±4.5 41.32±11.3 0.634 0.199
TT (n=73) 44.86±4.6 43.14±11.9 0.634 0.196
additive 0.634 0.973
+ GRIN2A rs1969060 TT (n=745) 44.83±4.5 42.00±11.9 0.634 0.160
TC (n=292) 45.24±5.1 41.67±11.5 0.634 0.203
CC (n=32) 45.75±4.2 40.66±11.5 0.634 0.645
additive 0.634 0.172
+ GRIN2A rs2650427 CC (n=374) 44.99±4.0 41.40±11.9 0.634 0.125
CT (n=512) 44.94±5.2 41.99±11.9 0.634 0.891
TT (n=183) 42.51±4.2 43.14±10.9 0.635 0.031
additive 0.635 0.028
Model Genotypes CAGmean ± SD motor AO
mean ± SD		 R²* P value
HD CAG 40-77 ( n =538) 44.72±4.0 43.39±11.6 0.620 <0.0005
+ GRIN2B C2664T (rs1806201) CC (n=274) 44.52±3.8 44.41±11.8 0.622 0.099
CT (n=221) 44.96±4.1 41.98±11.1 0.623 0.046
TT (n=43) 44.77±4.9 44.07±12.4 0.620 0.560
additive 0.621 0.296
+ GRIN2A rs1969060 TT (n=373) 44.51±3.6 43.79±11.5 0.620 0.824
TC (n=153) 45.32±4.9 42.19±11.9 0.620 0.934
CC (n=12) 43.75±2.5 46.25±9.5 0.620 0.658
additive 0.620 0.744
+ GRIN2A rs2650427 CC (n=181) 44.15±3.8 41.99±11.8 0.620 0.362
CT (n=259) 44.48±4.1 44.00±11.9 0.620 0.792
TT (n=98) 44.60±4.2 44.34±10.4 0.621 0.143
additive 0.621 0.158
Model Genotypes CAGmean ± SD psychiatric AOmean ± SD R²* P value
HD CAG 40-67 ( n =241) 44.73±4.1 39.86±10.8 0.515 <0.0005
+ GRIN2B C2664T (rs1806201) CC (n=139) 44.81±4.4 39.50±11.3 0.513 0.964
CT (n=90) 44.74±3.8 39.79±10.5 0.514 0.607
TT (n=12) 43.67±2.1 44.58±9.6 0.517 0.211
additive 0.514 0.618
+ GRIN2A rs1969060 TT (n=172) 44.79±4.1 39.01±10.9 0.523 0.026
TC (n=63) 44.01±3.7 42.78±9.8 0.523 0.033
CC (n=6) 49.50±6.8 33.50±15.5 0.514 0.649
additive 0.522 0.037
+ GRIN2A rs2650427 CC (n=83) 44.79±4.0 39.42±11.3 0.514 0.504
CT (n=120) 44.24±3.8 40.90±10.5 0.514 0.702
TT (n=38) 43.13±5.1 37.53±10.8 0.514 0.724
additive 0.514 0.514
Model Genotypes CAGmean ± SD cognitive AOmean ± SD R²* P value
HD CAG 40-89 ( n =112) 46.34±7.8 38.60±13.1 0.765 <0.0005
+ GRIN2B C2664T (rs1806201) CC (n=54) 46.76±8.5 37.89±14.2 0.763 0.621
CT (n=55) 45.74±7.1 39.73±11.9 0.763 0.530
TT (n=3) 50.00±6.2 30.67±14.0 0.763 0.682
additive 0.763 0.742
+ GRIN2A rs1969060 TT (n=74) 46.24±7.8 38.95±14.1 0.763 0.682
TC (n=31) 46.74±8.5 37.68±11.4 0.763 0.799
CC (n=7) 45.71±3.8 39.00±10.4 0.763 0.741
additive 0.763 0.650
+ GRIN2A rs2650427 CC (n=40) 45.55±4.9 37.80±12.4 0.770 0.054
CT (n=55) 47.67±10.0 36.87±13.2 0.763 0.742
TT (n=17) 43.9±3.2 46.06±12.3 0.772 0.033
additive 0.775 0.014

Table 1 The variability in AO attributable to the CAG repeat length was assessed by linear regression using the logarithmically transformed AO as the dependent variable and GRIN genotypes as independent variables. *R 2 illustrates the relative improvement of the regression model, when the genotypes are considered in addition to the CAG repeats.

In order to control the effect of sex-specific associations, we further analysed each combination of genotype with sex, but there was no trend towards significance. Moreover, on average, psychiatric and cognitive symptoms significantly predate clinical motor onset by 3.5 and 4.8 years (p< 0.001), thus confirming that affective and cognitive symptoms could be early manifestations of neuronal dysfunction.

Discussion

Of the three polymorphisms tested, GRIN2A rs2650427 showed the most consistent evidence of replication in the EHDN Registry study sample. This is in accordance with another replication study in the large set of kindreds from Venezuela, where GRIN2A variation also explained a small but considerable amount of additional variance in residual AO. [5]

Yet, the interpretation of the association of cognitve AO with the GRIN2A rs2650427 polymorphism should be considered with caution since the sample size of this subgroub (n=112) is too small to provide the statistical power required.

Unfortunately, none of the SNPs associated has been validated functionally and it is most likely that the polymorphisms analysed are not the functional variations, but represent markers in linkage disequilibrium with variations that modify the AO. Although, synonymous SNPs like GRIN2B rs1806201 might be pathogenetically relevant via influencing mRNA splicing, protein stability and structure.

The failure to replicate the sex-specific effect of rs1806201 suggests that the original observation may have been false positive, emphasizing the need for stringent statistical thresholds. On the other hand, since linkage disequilibrium is not uniform across populations, the mixed ancestry in the EHDN REGISTRY study sample could account for heterogeneous results. Inconsistent results may also occur because of difficulties in exact AO definitions. The data stresses the need for precise phenotyping in order to reduce heterogeneity, and to facilitate the discovery of clinically relevant biological pathways.

Although the associations replicated explain only a small fraction of the variance of AO, the observed correlations with HD phenotypes demonstrate that GRIN2A and GRIN2B remain promising candidate genes, worth to be studied further in more detail.

Acknowledgments

The authors thank all EHDN Registry Study Group investigators for collecting the data and all participating patients for their time and efforts.

Correspondence to Dr Larissa Arning, Ruhr-University, Department of Human Genetics, Universitätsstr. 150, MA5/39, 44801 Bochum, Germany, [email protected]

Competing interests

The authors have declared that no competing interests exist.

Funding information

The European Huntington’s Disease Network is funded by CHDI Foundation, Inc. CS was supported by FoRUM grant K040-09.

Ethics approval

This study was conducted with the approval of the local ethics committee of the different clinical centres.

Expansion of Collaborator List

Investigators of the European Huntington’s Disease Network

K Barth, Language coordinator

M Bascuñana Garde, Language coordinator

R Bos, Language coordinator

D Ecker, Language coordinator

OJ Handley, Language coordinator

N Heinonen, Language coordinator

C Held, Language coordinator

M Laurà, Language coordinator

A Martínez Descals, Language coordinator

T Mestre, Language coordinator

D Monza, Language coordinator

J Naji, Language coordinator

M Orth, Language coordinator

H Padieu, Language coordinator

S Pro Koivisto, Language coordinator

A Rialland, Language coordinator

P Sasinková, Language coordinator

P Trigo Cubillo, Language coordinator

M van Walsem, Language coordinator

M-N Witjes-Ané, Language coordinator

D Zielonka, Language coordinator

Raphael M. Bonelli, LKH Graz, Abteilung für Psychiatrie, Austria

Brigitte Herranhof, LKH Graz, Abteilung für Psychiatrie, Austria

Anna Hödl, LKH Graz, Abteilung für Psychiatrie, Austria

Hans-Peter Kapfhammer, LKH Graz, Abteilung für Psychiatrie, Austria

Michael Koppitz, LKH Graz, Abteilung für Psychiatrie, Austria

Markus Magnet, LKH Graz, Abteilung für Psychiatrie, Austria

Daniela Otti, LKH Graz, Abteilung für Psychiatrie, Austria

Annamaria Painold, LKH Graz, Abteilung für Psychiatrie, Austria

Karin Reisinge, LKH Graz, Abteilung für Psychiatrie, Austria

Florian Brugger,Universitätsklinik für Neurologie, Innsbruck, Austria

Caroline Hepperger, Universitätsklinik für Neurologie, Innsbruck, Austria

Anna Hotter, Universitätsklinik für Neurologie, Innsbruck, Austria

Philipp Mahlknecht, Universitätsklinik für Neurologie, Innsbruck, Austria

Michael Nocker, Universitätsklinik für Neurologie, Innsbruck, Austria

Klaus Seppi, Universitätsklinik für Neurologie, Innsbruck, Austria

Gregor Wenning, Universitätsklinik für Neurologie, Innsbruck, Austria

Pascale Ribaï, Institut de Pathologie et de Génétiqu, C

Christine Verellen-Dumoulin ,Institut de Pathologie et de Génétiqu, Charleroi, Belgiu

Jiří Klempíř, Centrum extrapyramidových onemocnění, Prague, Czech Republic

Martin Kucharik, Centrum extrapyramidových onemocnění, Prague, Czech Republic

Jan Roth, Centrum extrapyramidových onemocnění, Prague, Czech Republic

Lis Hasholt, Hukommelsesklinikken, Rigshospitalet, Copehnhagen, Denmark

Lena E. Hjermind, Hukommelsesklinikken, Rigshospitalet, Copehnhagen, Denmark

Oda Jakobsen, Hukommelsesklinikken, Rigshospitalet, Copehnhagen, Denmark

Jørgen E Nielsen, Hukommelsesklinikken, Rigshospitalet, Copehnhagen, Denmark

Anne Nørremølle, Hukommelsesklinikken, Rigshospitalet, Copehnhagen, Denmark

Sven Asger Sørensen, Hukommelsesklinikken, Rigshospitalet, Copehnhagen, Denmark

Jette Stokholm, Hukommelsesklinikken, Rigshospitalet, Copehnhagen, Denmark

Heli Hiivola, Rehabilitation Centre Suvituuli, Turku-Suvituuli, Finland

Kirsti Martikainen, Rehabilitation Centre Suvituuli, Turku-Suvituuli, Finland

Katri Tuuha, Rehabilitation Centre Suvituuli, Turku-Suvituuli, Finland

Christoph Michael Kosinski, Universitätsklinikum Aachen, Neurologische Klinik, Germany

Daniela Probst, Universitätsklinikum Aachen, Neurologische Klinik, Germany

Christian Sass, Universitätsklinikum Aachen, Neurologische Klinik, Germany

Johannes Schiefer, Universitätsklinikum Aachen, Neurologische Klinik, Germany

Christiane Schlangen, Universitätsklinikum Aachen, Neurologische Klinik, Germany

Cornelius J. Werner, Universitätsklinikum Aachen, Neurologische Klinik, Germany

Herwig Lange, Reha Zentrum in Dinslaken im Gesundheitszentrums Lang, Dinslake, Germany

Matthias Löhle, Universitätsklinikum Carl Gustav Carus an der Technischen Universität Dresden, Klinik und Poliklinik für Neurologie, Dresden, Germany

Alexander Storch, Universitätsklinikum Carl Gustav Carus an der Technischen Universität Dresden, Klinik und Poliklinik für Neurologie, Dresden, Germany

Anett Wolz, Universitätsklinikum Carl Gustav Carus an der Technischen Universität Dresden, Klinik und Poliklinik für Neurologie, Dresden, Germany

Martin Wolz, Universitätsklinikum Carl Gustav Carus an der Technischen Universität Dresden, Klinik und Poliklinik für Neurologie, Dresden, Germany

Johann Lambeck, Universitätsklinik Freiburg, Neurologie, Freiburg, Germany

Birgit Zucker, Universitätsklinik Freiburg, Neurologie, Freiburg, Germany

Alexander Münchau, Universitätsklinikum Hamburg-Eppendorf, Klinik und Poliklinik für Neurologie, Hamburg, Germany

Lars Stubbe, Universitätsklinikum Hamburg-Eppendorf, Klinik und Poliklinik für Neurologie, Hamburg, Germany

Simone Zittel, Universitätsklinikum Hamburg-Eppendorf, Klinik und Poliklinik für Neurologie, Hamburg, Germany

Walburgis Heinicke, Psychatrium Heiligenhafen, Germany

Bernhard Longinus, Klinik für Psychiatrie und Psychotherapie Marburg-Süd, Germany

Alexander Peinemann, Huntington-Ambulanz im Neuro-Kopfzentrum – Klinikum rechts der Isar der Neurologischen Klinik und Poliklinik der Technischen Universität München, Germany

Michael Städtler, Huntington-Ambulanz im Neuro-Kopfzentrum – Klinikum rechts der Isar der Neurologischen Klinik und Poliklinik der Technischen Universität München, Germany

Adolf Weindl, Huntington-Ambulanz im Neuro-Kopfzentrum – Klinikum rechts der Isar der Neurologischen Klinik und Poliklinik der Technischen Universität München, Germany

Stefan Bohlen, Universitätsklinikum Münster, Klinik und Poliklinik für Neurologie, Münster, Germany

Herwig Lange, Universitätsklinikum Münster, Klinik und Poliklinik für Neurologie, Münster, Germany

Ralf Reilmann, Universitätsklinikum Münster, Klinik und Poliklinik für Neurologie, Münster, Germany

Antonie Beister, Isar-Amper-Klinikum – Klinik Taufkirchen (Vils), Germany

Matthias Dose, Isar-Amper-Klinikum – Klinik Taufkirchen (Vils), Germany

Kathrin Hammer, Isar-Amper-Klinikum – Klinik Taufkirchen (Vils), Germany

Gabriele Leythaeuser, Isar-Amper-Klinikum – Klinik Taufkirchen (Vils), Germany

Ralf Marquard, Isar-Amper-Klinikum – Klinik Taufkirchen (Vils), Germany

Tina Raab, Isar-Amper-Klinikum – Klinik Taufkirchen (Vils), Germany

Caroline Schrenk, Isar-Amper-Klinikum – Klinik Taufkirchen (Vils), Germany

Michele Schuierer, Isar-Amper-Klinikum – Klinik Taufkirchen (Vils), Germany

Alexandra Wiedemann, Isar-Amper-Klinikum – Klinik Taufkirchen (Vils), Germany

Antonie Beister, Taufkirchen, Germany

Matthias Dose, Taufkirchen, Germany

Kathrin Hammer, Taufkirchen, Germany

Gabriele Leythaeuser, Taufkirchen, Germany

Ralf Marquard, Taufkirchen, Germany

Tina Raab, Taufkirchen, Germany

Caroline Schrenk, Taufkirchen, Germany

Michele Schuierer, Taufkirchen, Germany

Alexandra Wiedemann, Taufkirchen, Germany

Daniel Ecker, Universitätsklinikum Ulm, Neurologie, Ulm, Germany

Carolin Eschenbach, Universitätsklinikum Ulm, Neurologie, Ulm, Germany

Bernhard Landwehrmeyer, Universitätsklinikum Ulm, Neurologie, Ulm, Germany

Franziska Lezius, Universitätsklinikum Ulm, Neurologie, Ulm, Germany

Michael Orth, Universitätsklinikum Ulm, Neurologie, Ulm, Germany

Sonja Trautmann, Universitätsklinikum Ulm, Neurologie, Ulm, Germany

Claudia Cormio, Dipartimento di Scienze Neurologiche e Psichiatriche Universita’ di Bari, Italy

Olimpia Difruscolo, Dipartimento di Scienze Neurologiche e Psichiatriche Universita’ di Bari, Italy

Marina de Tommaso, Dipartimento di Scienze Neurologiche e Psichiatriche Universita’ di Bari, Italy

Vittorio Sciruicchio, Dipartimento di Scienze Neurologiche e Psichiatriche Universita’ di Bari, Italy

Claudia Serpino, Dipartimento di Scienze Neurologiche e Psichiatriche Universita’ di Bari, Italy

Elisabetta Bertini, Neurologia I- Unita’ di Neurogenetica Departimento di Neurologia e Psichiatria, Universita’ di Firenze, Italy

Claudia Mechi, Neurologia I- Unita’ di Neurogenetica Departimento di Neurologia e Psichiatria, Universita’ di Firenze, Italy

Marco Paganini, Neurologia I- Unita’ di Neurogenetica Departimento di Neurologia e Psichiatria, Universita’ di Firenze, Italy

Sivia Piacentini, Neurologia I- Unita’ di Neurogenetica Departimento di Neurologia e Psichiatria, Universita’ di Firenze, Italy

Maria Romoli, Neurologia I- Unita’ di Neurogenetica Departimento di Neurologia e Psichiatria, Universita’ di Firenze, Italy

Sandro Sorbi, Neurologia I- Unita’ di Neurogenetica Departimento di Neurologia e Psichiatria, Universita’ di Firenze, Italy

Giovanni Abbruzzese, Dipartimento di Neuroscienze, Oftalmologia e Genetica (DiNOG), Università di Genova, Italy

Emilio Di Maria, Dipartimento di Neuroscienze, Oftalmologia e Genetica (DiNOG), Università di Genova, Italy

Monica Bandettini di Poggio Giovanna Ferrandes, Dipartimento di Neuroscienze, Oftalmologia e Genetica (DiNOG), Università di Genova, Italy

Paola Mandich, Dipartimento di Neuroscienze, Oftalmologia e Genetica (DiNOG), Università di Genova, Italy

Roberta Marchese, Dipartimento di Neuroscienze, Oftalmologia e Genetica (DiNOG), Università di Genova, Italy

Alberto Albanese, Fondazione IRCCS Istituto Neurologico C. Besta, Milan, Italy

Stefano Di Donato, Fondazione IRCCS Istituto Neurologico C. Besta, Milan, Italy

Caterina Mariotti, Fondazione IRCCS Istituto Neurologico C. Besta, Milan, Italy

Paola Soliveri, Fondazione IRCCS Istituto Neurologico C. Besta, Milan, Italy

Cinzia Gellera, Fondazione IRCCS Istituto Neurologico C. Besta, Milan, Italy

Daniela Monza, Fondazione IRCCS Istituto Neurologico C. Besta, Milan, Italy

Chiara Tomasello, Fondazione IRCCS Istituto Neurologico C. Besta, Milan, Italy

Lorenzo Nanetti, Fondazione IRCCS Istituto Neurologico C. Besta, Milan, Italy

Di Maio Luigi, Azienda Ospedaliera Universitaria Federico II – Dipartimento di Scienze Neurologiche, Naples, Italy

Giuseppe De Michele, Azienda Ospedaliera Universitaria Federico II – Dipartimento di Scienze Neurologiche, Naples, Italy

Carlo Rinaldi, Azienda Ospedaliera Universitaria Federico II – Dipartimento di Scienze Neurologiche, Naples, Italy

Cinzia Russo, Azienda Ospedaliera Universitaria Federico II – Dipartimento di Scienze Neurologiche, Naples, Italy

Elena Salvatore, Azienda Ospedaliera Universitaria Federico II – Dipartimento di Scienze Neurologiche, Naples, Italy

Tecla Tucci, Azienda Ospedaliera Universitaria Federico II – Dipartimento di Scienze Neurologiche, Naples, Italy

Ferdinando Squitieri, Neurogenetics Unit – IRCCS Neuromed, Pozzilli , Italy

Tiziana Martino, Neurogenetics Unit – IRCCS Neuromed, Pozzilli , Italy

Sara Orobello, Neurogenetics Unit – IRCCS Neuromed, Pozzilli , Italy

Silvia Alberti, Neurogenetics Unit – IRCCS Neuromed, Pozzilli , Italy

Francesca De Gregorio, Neurogenetics Unit – IRCCS Neuromed, Pozzilli , Italy

Valentina Codella, Neurogenetics Unit – IRCCS Neuromed, Pozzilli , Italy

Nunzia De Nicola, Neurogenetics Unit – IRCCS Neuromed, Pozzilli , Italy

Vittorio Maglione, Neurogenetics Unit – IRCCS Neuromed, Pozzilli , Italy

Anna Rita Bentivoglio, Istituto di Neurobiologia e Medicina Molecolare CNR/ Istituto di Neurologia, Dipartimento di Neuroscienze/ CNR Istituto di Scienze e Tecnologie della Cognizione, Rome, Italy

Alfonso Fasano, Istituto di Neurobiologia e Medicina Molecolare CNR/ Istituto di Neurologia, Dipartimento di Neuroscienze/ CNR Istituto di Scienze e Tecnologie della Cognizione, Rome, Italy

Marina Frontali, Istituto di Neurobiologia e Medicina Molecolare CNR/ Istituto di Neurologia, Dipartimento di Neuroscienze/ CNR Istituto di Scienze e Tecnologie della Cognizione, Rome, Italy

Arianna Guidubaldi, Istituto di Neurobiologia e Medicina Molecolare CNR/ Istituto di Neurologia, Dipartimento di Neuroscienze/ CNR Istituto di Scienze e Tecnologie della Cognizione, Rome, Italy

Tamara Ialongo, Istituto di Neurobiologia e Medicina Molecolare CNR/ Istituto di Neurologia, Dipartimento di Neuroscienze/ CNR Istituto di Scienze e Tecnologie della Cognizione, Rome, Italy

Gioia Jacopini, Istituto di Neurobiologia e Medicina Molecolare CNR/ Istituto di Neurologia, Dipartimento di Neuroscienze/ CNR Istituto di Scienze e Tecnologie della Cognizione, Rome, Italy

Giovanna Loria, Istituto di Neurobiologia e Medicina Molecolare CNR/ Istituto di Neurologia, Dipartimento di Neuroscienze/ CNR Istituto di Scienze e Tecnologie della Cognizione, Rome, Italy

Carla Piano, Istituto di Neurobiologia e Medicina Molecolare CNR/ Istituto di Neurologia, Dipartimento di Neuroscienze/ CNR Istituto di Scienze e Tecnologie della Cognizione, Rome, Italy

Silvia Romano, Istituto di Neurobiologia e Medicina Molecolare CNR/ Istituto di Neurologia, Dipartimento di Neuroscienze/ CNR Istituto di Scienze e Tecnologie della Cognizione, Rome, Italy

Francesco Soleti, Istituto di Neurobiologia e Medicina Molecolare CNR/ Istituto di Neurologia, Dipartimento di Neuroscienze/ CNR Istituto di Scienze e Tecnologie della Cognizione, Rome, Italy

Maria Spadaro, Istituto di Neurobiologia e Medicina Molecolare CNR/ Istituto di Neurologia, Dipartimento di Neuroscienze/ CNR Istituto di Scienze e Tecnologie della Cognizione, Rome, Italy

Paola Zinzi , Istituto di Neurobiologia e Medicina Molecolare CNR/ Istituto di Neurologia, Dipartimento di Neuroscienze/ CNR Istituto di Scienze e Tecnologie della Cognizione, Rome, Italy

Arvid Heiberg, Rikshospitalet, Dept. of Medical Genetics, Oslo-RH, Norway

Marleen R van Walsem, Rikshospitalet, Dept. of Medical Genetics, Oslo-RH, Norway

Kathrine Bjørgo, Ullevål University Hospital, Oslo, Norway

Madelein Fannemel, Ullevål University Hospital, Oslo, Norway

Per Gørvell, Ullevål University Hospital, Oslo, Norway

Lars Retterstøl, Ullevål University Hospital, Oslo, Norway

Inga Bjørnevoll, St. Olavs Hospital, Trondheim , Norway

Sigrid Botne Sando, St. Olavs Hospital, Trondheim , Norway

Jaroslaw Slawek, Specialistic Hospital, Gdansk Zaspa, Gdansk, Poland

Witold Soltan, Specialistic Hospital, Gdansk Zaspa, Gdansk, Poland

Emilia Sitek, Specialistic Hospital, Gdansk Zaspa, Gdansk, Poland

Magdalena Boczarska-Jedynak, Silesian Medical University Katowice, Poland

Barbara Jasinska-Myga, Silesian Medical University Katowice, Poland

Gregorz Opala, Silesian Medical University Katowice, Poland

Andrzej Szczudlik, Krakowska Akademia Neurologii, Krakow, Poland

Monika Rudzińska, Krakowska Akademia Neurologii, Krakow, Poland

Magdalena Wójcik, Krakowska Akademia Neurologii, Krakow, Poland

Krzysztof Banaszkiewicz, Krakowska Akademia Neurologii, Krakow, Poland

Malgorzata Krawczyk, Krakowska Akademia Neurologii, Krakow, Poland

Daniel Zielonka, Medical University of Poznań, Poland

Jerzy Marcinkowski, Medical University of Poznań, Poland

Anna Ciesielska, Medical University of Poznań, Poland

Justyna Sempołowicz, Medical University of Poznań, Poland

Anna Bryl, Medical University of Poznań, Poland

Aneta Klimberg, Medical University of Poznań, Poland

Piotr Janik, Medical University of Warsaw, Neurology, Warsaw-MU, Poland

Anna Kalbarczyk, Medical University of Warsaw, Neurology, Warsaw-MU, Poland

Hubert Kwiecinski, Medical University of Warsaw, Neurology, Warsaw-MU, Poland

Zygmunt Jamrozik, Medical University of Warsaw, Neurology, Warsaw-MU, Poland

Grzegorz Witkowski, Institute of Psychiatry and Neurology Dep. of Genetics, Dep. of Neurology, Warsaw-IPiN, Poland

Danuta Ryglewicz, Institute of Psychiatry and Neurology Dep. of Genetics, Dep. of Neurology, Warsaw-IPiN, Poland

Jakub Antczak, Institute of Psychiatry and Neurology Dep. of Genetics, Dep. of Neurology, Warsaw-IPiN, Poland

Maria Rakowicz, Institute of Psychiatry and Neurology Dep. of Genetics, Dep. of Neurology, Warsaw-IPiN, Poland

Katarzyna Jachinska, Institute of Psychiatry and Neurology Dep. of Genetics, Dep. of Neurology, Warsaw-IPiN, Poland

Elzbieta Zdzienicka, Institute of Psychiatry and Neurology Dep. of Genetics, Dep. of Neurology, Warsaw-IPiN, Poland

Przemyslaw Richter, Institute of Psychiatry and Neurology Dep. of Genetics, Dep. of Neurology, Warsaw-IPiN, Poland

Jacek Zaremba, Institute of Psychiatry and Neurology Dep. of Genetics, Dep. of Neurology, Warsaw-IPiN, Poland

Miguel Coelho, Neurological Clinical Research Unit, Institute of Molecular Medicine, Lisbon-Santa Maria, Portugal

Joaquim J Ferreira, Neurological Clinical Research Unit, Institute of Molecular Medicine, Lisbon-Santa Maria, Portugal

Tiago Mestre, Neurological Clinical Research Unit, Institute of Molecular Medicine, Lisbon-Santa Maria, Portugal

Mário M Rosa, Neurological Clinical Research Unit, Institute of Molecular Medicine, Lisbon-Santa Maria, Portugal

Anabela Valadas, Neurological Clinical Research Unit, Institute of Molecular Medicine, Lisbon-Santa Maria, Portugal

Miguel Gago, Hospital São João E.P.E., Porto-São João, Portugal

Carolina Garrett, Hospital São João E.P.E., Porto-São João, Portugal

Maria Rosalia Guerra, Hospital São João E.P.E., Porto-São João, Portugal

Francisco J Barrero, Hospital Universitario San Cecilio, Neurología, Granada, Spain

Blas Morales, Hospital Universitario San Cecilio, Neurología, Granada, Spain

José Luis López-Sendón Moreno, Hospital Universitario Ramón y Cajal, Neurología, Madrid, Spain

Esther Cubo, Servicio de Neurología Hospital General Yagüe, Burgos, Spain

Natividad Mariscal, Servicio de Neurología Hospital General Yagüe, Burgos, Spain

Jesús Sánchez, Servicio de Neurología Hospital General Yagüe, Burgos, Spain

Rocío García-Ramos García, Hospital Clínico Universitario San Carlos, Madrid-Clinico, Spain

Clara Villanueva, Hospital Clínico Universitario San Carlos, Madrid-Clinico, Spain

Purificacion Pin Quiroga, Hospital Clínico Universitario San Carlos, Madrid-Clinico, Spain

Mónica Bascuñana, Hospital Ramón y Cajal, Neurología, Madrid RYC, Spain

Patricia Trigo Cubillo, Hospital Ramón y Cajal, Neurología, Madrid RYC, Spain

Marta Fatàas, Hospital Ramón y Cajal, Neurología, Madrid RYC, Spain

José Luis López Moreno, Hospital Ramón y Cajal, Neurología, Madrid RYC, Spain

Guillermo García Ribas, Hospital Ramón y Cajal, Neurología, Madrid RYC, Spain

Christine Schwarz, Hospital Ramón y Cajal, Neurología, Madrid RYC, Spain

Justo García de Yébenes, Hospital Ramón y Cajal, Neurología, Madrid RYC, Spain

María José Saiz Artiga, Madrid-Fundación Jiménez Díaz, Madrid FJD, Spain

Asunción Martínez-Descals, Madrid-Fundación Jiménez Díaz, Madrid FJD, Spain

Pedro J García Ruíz, Madrid-Fundación Jiménez Díaz, Madrid FJD, Spain

Vicenta Sánchez, Madrid-Fundación Jiménez Díaz, Madrid FJD, Spain

Lorenza Fortuna Alcaraz, Hospital Universitario Virgen de la Arrixaca, Murcia, Spain

María Fuensanta Noguera Perea, Hospital Universitario Virgen de la Arrixaca, Murcia, Spain

María Martirio Antequera Torres, Hospital Universitario Virgen de la Arrixaca, Murcia, Spain

Laura Vivancos Moreau, Hospital Universitario Virgen de la Arrixaca, Murcia, Spain

Ana Rojo Sebastian, Barcelona-Hospital Mútua de Terrassa, Spain

Miquel Aguilar Barbera, Barcelona-Hospital Mútua de Terrassa, Spain

Dolors Badenes Guia, Barcelona-Hospital Mútua de Terrassa, Spain

Laura Casas Hernanz, Barcelona-Hospital Mútua de Terrassa, Spain

Gemma Tome Carruesco, Barcelona-Hospital Mútua de Terrassa, Spain

Esther Suarez San Martin, Barcelona-Hospital Mútua de Terrassa, Spain

Judit López Catena, Barcelona-Hospital Mútua de Terrassa, Spain

Jordi Bas, Hospital Universitari de Bellvitge, Barcelona-Bellvitge, Spain

Matilde Calopa, Hospital Universitari de Bellvitge, Barcelona-Bellvitge, Spain

Núria Busquets, Hospital Universitari de Bellvitge, Barcelona-Bellvitge, Spain

Penelope Navas Arques, Hospital Son Dureta, Palma, Spain

Aranzazú Gorospe, Hospital Son Dureta, Palma, Spain

Inés Legarda, Hospital Son Dureta, Palma, Spain

María José Torres Rodríguez, Hospital Son Dureta, Palma, Spain

Barbara Vives, Hospital Son Dureta, Palma, Spain

Fátima Carrillo, Hospital Virgen del Rocío, Sevilla, Spain

Pablo Mir, Hospital Virgen del Rocío, Sevilla, Spain

María José Lama Suarez, Hospital Virgen del Rocío, Sevilla, Spain

Ghada Loutfi, Norrlands Universitet Sjukhus, Department of Neurology, Umeå, Sweden

Eva-Lena Stattin, Norrlands Universitet Sjukhus, Department of Neurology, Umeå, Sweden

Laila Westman, Norrlands Universitet Sjukhus, Department of Neurology, Umeå, Sweden

Birgitta Wikström, Norrlands Universitet Sjukhus, Department of Neurology, Umeå, Sweden

Sven Pålhagen, Karolinska-University Hospital, Stockholm, Sweden

Elisabeth Björnsson, Karolinska-University Hospital, Stockholm, Sweden

Jean-Marc Burgunder, Neurologische Klinik des Inselspitals, Bern, Switzerland

Irene Romero, Zentrum für Bewegungsstörungen, Neurologische Klinik und Poliklinik, Bern, Switzerland

Michael Schüpbach, Zentrum für Bewegungsstörungen, Neurologische Klinik und Poliklinik, Bern, Switzerland

Sabine Weber Zaugg, Zentrum für Bewegungsstörungen, Neurologische Klinik und Poliklinik, Bern, Switzerland

Monique S.E. van Hout, Medisch Spectrum Twente, Ensched, The Netherlands

Jeroen P.P. van Vugt, Medisch Spectrum Twente, Ensched, The Netherlands

A. Marit de Weert, Medisch Spectrum Twente, Ensched, The Netherlands

J.J.W. Bolwijn, Polikliniek Neurologie, Groningen, The Netherlands

M. Dekker, Polikliniek Neurologie, Groningen, The Netherlands

K.L. Leenders, Polikliniek Neurologie, Groningen, The Netherlands

J.C.H. van Oostrom, Polikliniek Neurologie, Groningen, The Netherlands

Reineke Bos, Leiden University Medical Centre, Leiden, The Netherlands

Eve M. Dumas, Leiden University Medical Centre, Leiden, The Netherlands

Caroline K. Jurgens, Leiden University Medical Centre, Leiden, The Netherlands

Simon J. A. van den Bogaard, Leiden University Medical Centre, Leiden, The Netherlands

Raymund A.C. Roos, Leiden University Medical Centre, Leiden, The Netherlands

Marie-Noëlle Witjes-Ané, Leiden University Medical Centre, Leiden, The Netherlands

Berry Kremer, Universitair Medisch Centrum St. Radboud, Neurology, Nijmegen, The Netherlands

C.C.P. Verstappen, Universitair Medisch Centrum St. Radboud, Neurology, Nijmegen, The Netherlands

Jenny de Souza, The Barberry Centre, Dept of Psychiatry, Birmingham, UK

Hugh Rickards, The Barberry Centre, Dept of Psychiatry, Birmingham, UK

Jan Wright, The Barberry Centre, Dept of Psychiatry, Birmingham, UK

Roger A. Barker, Cambridge Centre for Brain Repair, Forvie Site, Cambridge, UK

Kate Fisher, Cambridge Centre for Brain Repair, Forvie Site, Cambridge, UK

Anna Olivia Goyder Goodman, Cambridge Centre for Brain Repair, Forvie Site, Cambridge, UK

Susan Hill, Cambridge Centre for Brain Repair, Forvie Site, Cambridge, UK

Ann Kershaw, Cambridge Centre for Brain Repair, Forvie Site, Cambridge, UK

Sarah Mason, Cambridge Centre for Brain Repair, Forvie Site, Cambridge, UK

Nicole Paterson, Cambridge Centre for Brain Repair, Forvie Site, Cambridge, UK

Lucy Raymond, Cambridge Centre for Brain Repair, Forvie Site, Cambridge, UK

Johnathan Bisson, The Institute of Medical Genetics, University Hospital of Wales, Cardiff, UK

Monica Busse, The Institute of Medical Genetics, University Hospital of Wales, Cardiff, UK

Lynda Ellison-Rose, The Institute of Medical Genetics, University Hospital of Wales, Cardiff, UK

Olivia Handley, The Institute of Medical Genetics, University Hospital of Wales, Cardiff, UK

Sarah Hunt, The Institute of Medical Genetics, University Hospital of Wales, Cardiff, UK

Jenny Naji, The Institute of Medical Genetics, University Hospital of Wales, Cardiff, UK

Kathleen Price, The Institute of Medical Genetics, University Hospital of Wales, Cardiff, UK

Anne Rosser, The Institute of Medical Genetics, University Hospital of Wales, Cardiff, UK

Stephen Dunnett, The Institute of Medical Genetics, University Hospital of Wales, Cardiff, UK

Maureen Edwards, Molecular Medicine Centre, Western General Hospital, Department of Clinical Genetics, Edinburgh, UK

Paul A. De Sousa, Molecular Medicine Centre, Western General Hospital, Department of Clinical Genetics, Edinburgh, UK

Teresa Hughes (Scottish Huntington´s Association), Molecular Medicine Centre, Western General Hospital, Department of Clinical Genetics, Edinburgh, UK

Marie McGill, Molecular Medicine Centre, Western General Hospital, Department of Clinical Genetics, Edinburgh, UK

Pauline Pearson, Molecular Medicine Centre, Western General Hospital, Department of Clinical Genetics, Edinburgh, UK

Mary Porteous, Molecular Medicine Centre, Western General Hospital, Department of Clinical Genetics, Edinburgh, UK

Paul Smith (Scottish Huntington´s Association), Molecular Medicine Centre, Western General Hospital, Department of Clinical Genetics, Edinburgh, UK

Adam Zeman, Molecular Medicine Centre, Western General Hospital, Department of Clinical Genetics, Edinburgh, UK

Nicol Lambord, Heavitree Hospital, Exeter , UK

Julia Rankin, Heavitree Hospital, Exeter , UK

Liz Burrows, Department of Neurology Gloucestershire Royal Hospital, Gloucester, UK

Amy Fletcher, Department of Neurology Gloucestershire Royal Hospital, Gloucester, UK

Fiona Laver, Department of Neurology Gloucestershire Royal Hospital, Gloucester, UK

Mark Silva, Department of Neurology Gloucestershire Royal Hospital, Gloucester, UK

Aileen Thomson, Department of Neurology Gloucestershire Royal Hospital, Gloucester, UK

Thomasin Andrews, Guy’s Hospital, London , UK

Andrew Dougherty, Guy’s Hospital, London , UK

Fred Kavalier, Guy’s Hospital, London , UK

Charlotte Golding, Guy’s Hospital, London , UK

Alison Lashwood, Guy’s Hospital, London , UK

Dene Robertson, Guy’s Hospital, London , UK

Deborah Ruddy, Guy’s Hospital, London , UK

Anna Whaite, Guy’s Hospital, London , UK

Michael Patton, St. Georges-Hospital, London, UK

Maria Patterson, St. Georges-Hospital, London, UK

Colin Bourne, Leicestershire Partnership Trust, Mill Lodge, Leicester, UK

Carole Clayton, Leicestershire Partnership Trust, Mill Lodge, Leicester, UK

Heather Dipple, Leicestershire Partnership Trust, Mill Lodge, Leicester, UK

Jackie Clapton, Leicestershire Partnership Trust, Mill Lodge, Leicester, UK

Janet Grant, Leicestershire Partnership Trust, Mill Lodge, Leicester, UK

Diana Gross, Leicestershire Partnership Trust, Mill Lodge, Leicester, UK

Caroline Hallam, Leicestershire Partnership Trust, Mill Lodge, Leicester, UK

Julia Middleton, Leicestershire Partnership Trust, Mill Lodge, Leicester, UK

Ann Murch, Leicestershire Partnership Trust, Mill Lodge, Leicester, UK

Dawn Patino, Leicestershire Partnership Trust, Mill Lodge, Leicester, UK

Thomasin Andrews, The National Hospital for Neurology and Neurosurgery, London, UK

Stefania Bruno, The National Hospital for Neurology and Neurosurgery, London, UK

Elvina Chu, The National Hospital for Neurology and Neurosurgery, London, UK

Karen Doherty, The National Hospital for Neurology and Neurosurgery, London, UK

Nayana Lahiri, The National Hospital for Neurology and Neurosurgery, London, UK

Marianne Novak, The National Hospital for Neurology and Neurosurgery, London, UK

Aakta Patel, The National Hospital for Neurology and Neurosurgery, London, UK

Sarah Tabrizi, The National Hospital for Neurology and Neurosurgery, London, UK

Rachel Taylor, The National Hospital for Neurology and Neurosurgery, London, UK

Thomas Warner, The National Hospital for Neurology and Neurosurgery, London, UK

Edward Wild, The National Hospital for Neurology and Neurosurgery, London, UK

Natalie Arran, Genetic Medicine, University of Manchester, Manchester Academic Health Sciences Centre and Central Manchester University Hospitals NHS Foundation Trust, Manchester, UK

David Craufurd, Genetic Medicine, University of Manchester, Manchester Academic Health Sciences Centre and Central Manchester University Hospitals NHS Foundation Trust, Manchester, UK

Ruth Fullam, Genetic Medicine, University of Manchester, Manchester Academic Health Sciences Centre and Central Manchester University Hospitals NHS Foundation Trust, Manchester, UK

Liz Howard, Genetic Medicine, University of Manchester, Manchester Academic Health Sciences Centre and Central Manchester University Hospitals NHS Foundation Trust, Manchester, UK

Susan Huson, Genetic Medicine, University of Manchester, Manchester Academic Health Sciences Centre and Central Manchester University Hospitals NHS Foundation Trust, Manchester, UK

Lucy Partington-Jones, Genetic Medicine, University of Manchester, Manchester Academic Health Sciences Centre and Central Manchester University Hospitals NHS Foundation Trust, Manchester, UK

Nichola Verstraelen (formerly Ritchie), Genetic Medicine, University of Manchester, Manchester Academic Health Sciences Centre and Central Manchester University Hospitals NHS Foundation Trust, Manchester, UK

Julie Snowden, Genetic Medicine, University of Manchester, Manchester Academic Health Sciences Centre and Central Manchester University Hospitals NHS Foundation Trust, Manchester, UK

Andrea Sollom, Genetic Medicine, University of Manchester, Manchester Academic Health Sciences Centre and Central Manchester University Hospitals NHS Foundation Trust, Manchester, UK

Cheryl Stopford, Genetic Medicine, University of Manchester, Manchester Academic Health Sciences Centre and Central Manchester University Hospitals NHS Foundation Trust, Manchester, UK

Jennifer Thompson, Genetic Medicine, University of Manchester, Manchester Academic Health Sciences Centre and Central Manchester University Hospitals NHS Foundation Trust, Manchester, UK

Leann Westmoreland, Genetic Medicine, University of Manchester, Manchester Academic Health Sciences Centre and Central Manchester University Hospitals NHS Foundation Trust, Manchester, UK

Andrea H Nemeth, Oxford Radcliffe Hospitals NHS Trust, Oxford, UK

Gill Siuda, Oxford Radcliffe Hospitals NHS Trust, Oxford, UK

Oliver Bandmann, The Royal Hallamshire Hospital, Sheffield, UK

Alyson Bradbury, The Royal Hallamshire Hospital, Sheffield, UK

Kay Fillingham, The Royal Hallamshire Hospital, Sheffield, UK

Isabella Foustanos, The Royal Hallamshire Hospital, Sheffield, UK

Katherine Tidswell,The Royal Hallamshire Hospital, Sheffield, UK

Oliver Quarrell, The Royal Hallamshire Hospital, Sheffield, UK