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1.  Baseline and longitudinal grey matter changes in newly diagnosed Parkinson’s disease: ICICLE-PD study 
Brain  2015;138(10):2974-2986.
Mild cognitive impairment in Parkinson’s disease (PDMCI) is associated with progression to dementia in a majority of patients. Mak et al. reveal accelerated cortical thinning in patients with PDMCI compared to non-cognitively impaired patients and healthy controls. Patterns of cortical thinning may constitute biomarkers for increased dementia risk.
Mild cognitive impairment in Parkinson’s disease (PDMCI) is associated with progression to dementia in a majority of patients. Mak et al. reveal accelerated cortical thinning in patients with PDMCI compared to non-cognitively impaired patients and healthy controls. Patterns of cortical thinning may constitute biomarkers for increased dementia risk.
Mild cognitive impairment in Parkinson’s disease is associated with progression to dementia (Parkinson’s disease dementia) in a majority of patients. Determining structural imaging biomarkers associated with prodromal Parkinson’s disease dementia may allow for the earlier identification of those at risk, and allow for targeted disease modifying therapies. One hundred and five non-demented subjects with newly diagnosed idiopathic Parkinson’s disease and 37 healthy matched controls had serial 3 T structural magnetic resonance imaging scans with clinical and neuropsychological assessments at baseline, which were repeated after 18 months. The Movement Disorder Society Task Force criteria were used to classify the Parkinson’s disease subjects into Parkinson’s disease with mild cognitive impairment (n = 39) and Parkinson’s disease with no cognitive impairment (n = 66). Freesurfer image processing software was used to measure cortical thickness and subcortical volumes at baseline and follow-up. We compared regional percentage change of cortical thinning and subcortical atrophy over 18 months. At baseline, cases with Parkinson’s disease with mild cognitive impairment demonstrated widespread cortical thinning relative to controls and atrophy of the nucleus accumbens compared to both controls and subjects with Parkinson’s disease with no cognitive impairment. Regional cortical thickness at baseline was correlated with global cognition in the combined Parkinson’s disease cohort. Over 18 months, patients with Parkinson’s disease with mild cognitive impairment demonstrated more severe cortical thinning in frontal and temporo-parietal cortices, including hippocampal atrophy, relative to those with Parkinson’s disease and no cognitive impairment and healthy controls, whereas subjects with Parkinson’s disease and no cognitive impairment showed more severe frontal cortical thinning compared to healthy controls. At baseline, Parkinson’s disease with no cognitive impairment converters showed bilateral temporal cortex thinning relative to the Parkinson’s disease with no cognitive impairment stable subjects. Although loss of both cortical and subcortical volume occurs in non-demented Parkinson’s disease, our longitudinal analyses revealed that Parkinson’s disease with mild cognitive impairment shows more extensive atrophy and greater percentage of cortical thinning compared to Parkinson’s disease with no cognitive impairment. In particular, an extension of cortical thinning in the temporo-parietal regions in addition to frontal atrophy could be a biomarker in therapeutic studies of mild cognitive impairment in Parkinson’s disease for progression towards dementia.
PMCID: PMC4671477  PMID: 26173861
Parkinson’s disease; neurodegeneration; neuroimaging; dementia
2.  Genetic impact on cognition and brain function in newly diagnosed Parkinson’s disease: ICICLE-PD study 
Brain  2014;137(10):2743-2758.
See Dujardin (doi:10.1093/brain/awu218) for a scientific commentary on this article. Nombela et al. present data from the ICICLE-PD study of cognition in newly diagnosed Parkinson’s disease. Consistent with the ‘Dual Syndrome’ hypothesis, impairments in executive function reflect a frontal dopaminergic syndrome modulated by COMT genotype, while visuospatial and memory deficits reflect disruption of temporo-parietal systems modulated by MAPT and APOE.
Parkinson’s disease is associated with multiple cognitive impairments and increased risk of dementia, but the extent of these deficits varies widely among patients. The ICICLE-PD study was established to define the characteristics and prevalence of cognitive change soon after diagnosis, in a representative cohort of patients, using a multimodal approach. Specifically, we tested the ‘Dual Syndrome’ hypothesis for cognitive impairment in Parkinson’s disease, which distinguishes an executive syndrome (affecting the frontostriatal regions due to dopaminergic deficits) from a posterior cortical syndrome (affecting visuospatial, mnemonic and semantic functions related to Lewy body pathology and secondary cholinergic loss). An incident Parkinson’s disease cohort (n = 168, median 8 months from diagnosis to participation) and matched control group (n = 85) were recruited to a neuroimaging study at two sites in the UK. All participants underwent clinical, neuropsychological and functional magnetic resonance imaging assessments. The three neuroimaging tasks (Tower of London, Spatial Rotations and Memory Encoding Tasks) were designed to probe executive, visuospatial and memory encoding domains, respectively. Patients were also genotyped for three polymorphisms associated with cognitive change in Parkinson’s disease and related disorders: (i) rs4680 for COMT Val158Met polymorphism; (ii) rs9468 for MAPT H1 versus H2 haplotype; and (iii) rs429358 for APOE-ε2, 3, 4. We identified performance deficits in all three cognitive domains, which were associated with regionally specific changes in cortical activation. Task-specific regional activations in Parkinson’s disease were linked with genetic variation: the rs4680 polymorphism modulated the effect of levodopa therapy on planning-related activations in the frontoparietal network; the MAPT haplotype modulated parietal activations associated with spatial rotations; and APOE allelic variation influenced the magnitude of activation associated with memory encoding. This study demonstrates that neurocognitive deficits are common even in recently diagnosed patients with Parkinson’s disease, and that the associated regional brain activations are influenced by genotype. These data further support the dual syndrome hypothesis of cognitive change in Parkinson’s disease. Longitudinal data will confirm the extent to which these early neurocognitive changes, and their genetic factors, influence the long-term risk of dementia in Parkinson’s disease. The combination of genetics and functional neuroimaging provides a potentially useful method for stratification and identification of candidate markers, in future clinical trials against cognitive decline in Parkinson’s disease.
PMCID: PMC4163033  PMID: 25080285
Parkinson’s disease; cognition; functional MRI; genetics
3.  The spectrum of nonmotor symptoms in early Parkinson disease 
Neurology  2013;80(3):276-281.
Nonmotor symptoms (NMS) are common in patients with established Parkinson disease (PD) but their frequency in early PD has not been extensively studied. Our aim was to determine the frequency of NMS in a cohort of patients with newly diagnosed PD.
A total of 159 patients with early PD and 99 healthy controls participated in this study. NMS were screened for using the Nonmotor Symptom Questionnaire. Other assessments included measures of motor disability (Movement Disorders Society–revised Unified Parkinson's Disease Rating Scale [MDS-UPDRS]), disease severity (Hoehn & Yahr staging), depression (Geriatric Depression Scale), and global cognitive function (Mini-Mental State Examination and Montreal Cognitive Assessment).
The PD group reported a significantly greater number of NMS compared with controls (8.4 [4.3] vs 2.8 [2.6]). In the PD group, the most commonly experienced NMS were excessive saliva, forgetfulness, urinary urgency, hyposmia, and constipation. Patients with higher MDS-UPDRS III scores and those with the postural instability gait subtype experienced a greater number of NMS.
NMS are common in early PD and reflect the multisystem nature of the disorder. Even in the earliest stages of PD, NMS may be detrimental to patients' functional status and sense of well-being.
PMCID: PMC3589180  PMID: 23319473
4.  Characterizing mild cognitive impairment in incident Parkinson disease 
Neurology  2014;82(4):308-316.
To describe the frequency of mild cognitive impairment (MCI) in Parkinson disease (PD) in a cohort of newly diagnosed incident PD cases and the associations with a panel of biomarkers.
Between June 2009 and December 2011, 219 subjects with PD and 99 age-matched controls participated in clinical and neuropsychological assessments as part of a longitudinal observational study. Consenting individuals underwent structural MRI, lumbar puncture, and genotyping for common variants of COMT, MAPT, SNCA, BuChE, EGF, and APOE. PD-MCI was defined with reference to the new Movement Disorder Society criteria.
The frequency of PD-MCI was 42.5% using level 2 criteria at 1.5 SDs below normative values. Memory impairment was the most common domain affected, with 15.1% impaired at 1.5 SDs. Depression scores were significantly higher in those with PD-MCI than the cognitively normal PD group. A significant correlation was found between visual Pattern Recognition Memory and cerebrospinal β-amyloid 1–42 levels (β standardized coefficient = 0.350; p = 0.008) after controlling for age and education in a linear regression model, with lower β-amyloid 1–42 and 1–40 levels observed in those with PD-MCI. Voxel-based morphometry did not reveal any areas of significant gray matter loss in participants with PD-MCI compared with controls, and no specific genotype was associated with PD-MCI at the 1.5-SD threshold.
In a large cohort of newly diagnosed PD participants, PD-MCI is common and significantly correlates with lower cerebrospinal β-amyloid 1–42 and 1–40 levels. Future longitudinal studies should enable us to determine those measures predictive of cognitive decline.
PMCID: PMC3929202  PMID: 24363137
5.  Neural correlates of attention‐executive dysfunction in lewy body dementia and Alzheimer's disease 
Human Brain Mapping  2015;37(3):1254-1270.
Attentional and executive dysfunction contribute to cognitive impairment in both Lewy body dementia and Alzheimer's disease. Using functional MRI, we examined the neural correlates of three components of attention (alerting, orienting, and executive/conflict function) in 23 patients with Alzheimer's disease, 32 patients with Lewy body dementia (19 with dementia with Lewy bodies and 13 with Parkinson's disease with dementia), and 23 healthy controls using a modified Attention Network Test. Although the functional MRI demonstrated a similar fronto‐parieto‐occipital network activation in all groups, Alzheimer's disease and Lewy body dementia patients had greater activation of this network for incongruent and more difficult trials, which were also accompanied by slower reaction times. There was no recruitment of additional brain regions or, conversely, regional deficits in brain activation. The default mode network, however, displayed diverging activity patterns in the dementia groups. The Alzheimer's disease group had limited task related deactivations of the default mode network, whereas patients with Lewy body dementia showed heightened deactivation to all trials, which might be an attempt to allocate neural resources to impaired attentional networks. We posit that, despite a common endpoint of attention‐executive disturbances in both dementias, the pathophysiological basis of these is very different between these diseases. Hum Brain Mapp 37:1254–1270, 2016. © 2015 The Authors Human Brain Mapping Published by Wiley Periodicals, Inc.
PMCID: PMC4784171  PMID: 26705763
Alzheimer's disease; attention; attention network test; executive; functional MRI; Lewy body dementia
6.  Semantic profiles in mild cognitive impairment associated with Alzheimer’s and Parkinson’s diseases 
Functional Neurology  2015;30(2):113-118.
The temporal and the prefrontal cortices have different roles in semantic information processing: the temporal lobe is where knowledge is stored (Graham and Hodges, 1997), whereas the prefrontal cortex is more specifically involved in executive aspects of semantic processing.
Relatively little is known about the semantic profiles of mild cognitive impairment (MCI) in Alzheimer’s disease (AD) and Parkinson’s disease (PD). This observational study investigated naming and semantic questionnaire performances in three groups of subjects: 10 patients with the amnestic-type MCI prodrome of AD (aMCI), 10 patients with early-stage executive-type MCI in PD (MCI-PD), and 10 normal subjects.
The MCI-PD subjects demonstrated inferior performances on a semantic questionnaire, whereas the aMCI group displayed modest difficulties in a naming task. These differences may be explained by topographical differences in pathological involvement. Since the frontal areas are more functionally impaired in PD, we hypothesize that the semantic deficit may be a consequence of a deficiency in control of semantic processing. On the other hand, the semantic deficit in aMCI may be related to a lexical-semantic storage dysfunction resulting from pathological involvement of the temporal lobe.
PMCID: PMC4610758  PMID: 26415783
Alzheimer’s disease; lexical damage; mild cognitive impairment; Parkinson’s disease; semantic damage
7.  Cognitive impairment in multiple system atrophy 
Consensus diagnostic criteria for multiple system atrophy consider dementia as a non-supporting feature, despite emerging evidence demonstrating that cognitive impairments are an integral part of the disease. Cognitive disturbances in multiple system atrophy occur across a wide spectrum from mild single domain deficits to impairments in multiple domains and even to frank dementia in some cases. Frontal-executive dysfunction is the most common presentation, while memory and visuospatial functions may also be impaired. Imaging and neuropathological findings support the concept that cognitive impairments in MSA originate from striatofrontal deafferentation with additional contributions from intrinsic cortical degeneration and cerebellar pathology. Based on a comprehensive evidence-based review we here propose future avenues of research that may ultimately lead to diagnostic criteria for cognitive impairment and dementia associated with multiple system atrophy.
PMCID: PMC4175376  PMID: 24753321
cognition; multiple system atrophy; neuropsychology
8.  Variation in complement protein C1q is not a major contributor to cognitive impairment in Parkinson’s disease 
Neuroscience Letters  2015;594:66-69.
•Cognitive decline is a strong hallmark of PD.•Genetic variation in C1Q – does not account for the cognitive decline seen in PD.•Genetic variation in C1Q – is unlikely to contribute to PD aetiology.
Traditional dogma regarding the brain as an immune exempt organ has changed in recent years. New research has highlighted the role of the classical complement cascade in both synaptic elimination and function, driven largely by the role of the pathway initiating protein C1q. Given the links between C1q and cognitive function we assessed the genetic variability of the C1q encoding genes: C1QA, C1QB and C1QC between PD patients and matched controls. Despite a strong link between C1Q/cognitive decline and PD/cognitive decline we were unable to find a link between common C1Q variation and PD. We conclude that common C1Q-A/B/C genetic variation is unlikely to contribute to cognitive decline or the missing heritability in PD.
PMCID: PMC4407898  PMID: 25817358
Parkinson’s disease; Cognitive decline
9.  Parkinson’s Disease Mild Cognitive Impairment: Application and Validation of the Criteria 
Journal of Parkinson's disease  2014;4(2):131-137.
Dementia in Parkinson’s disease (PD) is a serious health issue and a major concern for many patients. In most cases mild cognitive impairment (MCI) is considered a transitional stage between normal cognitive functioning and dementia which is of potential importance in the early identification of patients at risk for dementia. Recently, the Movement Disorder Society (MDS) proposed diagnostic criteria for MCI in PD (PD-MCI). These criteria comprise two operationalizations: Level I (based on an abbreviated assessment) and Level II (based on comprehensive neuropsychological evaluation permitting MCI subtyping). These criteria need to be validated.
This paper describes a project aiming to validate the MDS PD-MCI criteria by pooling and analyzing cross-sectional and longitudinal neuropsychological databases comprising ≥5,500 PD patients and ≥1,700 controls. After applying the MDS PD-MCI Level I and Level II criteria, rates of conversion to PD-dementia and predictive variables for conversion to PD-dementia will be established. This study will also assist in identifying whether revisions of the PD-MCI criteria are required.
PMCID: PMC4380013  PMID: 24296865
Parkinson disease; mild cognitive impairment; neuropsychological tests/standards; dementia; validation studies
10.  Severity of mild cognitive impairment in early Parkinson's disease contributes to poorer quality of life 
Parkinsonism & Related Disorders  2014;20(10):1071-1075.
Poor quality of life (QoL) is a feature of people with Parkinson's disease (PD) who develop dementia. The relationship between mild cognitive impairment in PD (PD-MCI) and QoL is less clear. To address this, we studied the impact of varying severities of cognitive impairment on QoL in a cohort of non-demented patients with early PD.
Patients with newly diagnosed PD (n = 219) and age and sex matched healthy controls (n = 99) completed a schedule of neuropsychological tests, in addition to scales assessing QoL (PDQ-39), depression, sleep, neuropsychiatric symptoms and a clinical examination. The Movement Disorder Society criteria were used to define and classify PD-MCI.
Participants with PD-MCI were significantly older than those with normal cognition, had more severe motor symptoms, scored higher for depression and had poorer quality of life. Logistic regression showed that mild cognitive impairment, independent of other factors, was an indicator of poorer QoL. Using cognitive performance 2.0 standard deviations (SD) below normative data as a cut-off to define PD-MCI, there was a significant difference in QoL scores between patients with PD-MCI and those classified as having normal cognition. Subjects with less severe mild cognitive impairment did not exhibit significant differences in QoL.
PD-MCI is a significant, independent factor contributing to poorer QoL in patients with newly diagnosed PD. Those classified with greatest impairment (2.0 SD below normal values) have lower QoL. This has implications for clinical practice and future interventions targeting cognitive impairments.
•Quality of life declines with increased severity of cognitive impairment in PD.•Mild cognitive impairment in PD (PD-MCI) independently contributes to poorer QoL.•PD-MCI at 2 standard deviations below controls had the greatest impact on QoL.•The optimal operational cut-off for PD-MCI may be 2 standard deviations.
PMCID: PMC4194347  PMID: 25074728
Parkinson's disease; Mild cognitive impairment; Quality of life
11.  Genetic variation of CHRNA4 does not modulate attention in Parkinson’s disease 
Neuroscience letters  2010;479(2):123-125.
Parkinson’s disease (PD) is a neurodegenerative disorder, characterised by cognitive decline and attentional impairment. Recently, variation in CHRNA4 (rs1044396) has been shown to affect visual and auditory function, affecting speed and attention, in healthy adults. An association between CHRNA4 variation and PD has not been shown. To determine the link between CHRNA4 variation and attentional deficit in PD. A genotype-phenotype correlation between the common CHRNA4:rs1044396 variant and several baseline parameters of attention was carried out in a large cohort of PD cases (n = 222) and controls (n = 159). We identified significant associations to measures of attention in PD patients compared to controls. However, we found no significant link to CHRNA4:rs1044396 genotypes to baseline attention variables in PD or in controls. We conclude that CHRNA4:rs1044396 genotypes do not significantly influence the attentional deficit found in PD patients. Contrary to previous studies, we also found no significant influence in healthy age-matched controls.
PMCID: PMC4038490  PMID: 20493238
Parkinson’s disease; Ageing; Cholinergic receptor; Attention
12.  Fall in circulating mononuclear cell mitochondrial DNA content in human sepsis 
Intensive care medicine  2010;36(6):956-962.
Loss of mitochondrial DNA (mtDNA) has been described in whole blood samples from a small number of patients with sepsis, but the underlying mechanism and clinical implications of this observation are not clear. We have investigated the cellular basis of the mtDNA depletion in sepsis, and determined clinical correlates with mtDNA depletion.
Whole blood samples were obtained from 147 consecutive patients with severe sepsis admitted to a General Critical Care Unit in a University Hospital and 83 healthy controls. In a separate study of 13 patients with severe sepsis, blood was obtained for immediate cell sorting by flow cytometry. MtDNA content was determined in whole blood DNA by PCR methods, and subsequently in the 13 samples where white cell subtypes were separated.
The mtDNA content of peripheral blood in human subjects was lower in patients with sepsis than controls (P < 0.0001). By studying leukocyte subsets in a subgroup of 13 patients, we showed that this was largely due to an increase in the proportion of circulating neutrophils, which contained ~3-fold less mtDNA than mononuclear leukocytes. However, isolated monocytes (P = 0.041) and lymphocytes (P = 0.021) from septic patients showed clear evidence of mtDNA depletion, which correlated with the APACHE II score (P = 0.015).
In severe sepsis much of the apparent whole blood mtDNA depletion is due to a change in the differential leukocyte count. However mtDNA depletion in mononuclear cells occurs in patients with sepsis and correlates with disease severity.
PMCID: PMC4034433  PMID: 20224905
Sepsis; Mitochondria; Copy number; Neutrophil; Monocyte; Lymphocyte
13.  No evidence of substantia nigra telomere shortening in Parkinson’s disease 
Neurobiology of aging  2011;32(11):2107.e3-2107.e5.
Telomeres are repetitive tracts of DNA which protect chromosomal integrity. Increased oxidative stress leads to shorter telomeres, which have been associated with several late-onset human diseases. Given independent evidence of oxidative stress and Parkinson’s disease (PD), and conflicting reports of the role of telomere length in PD, we measured telomere length in both PD peripheral blood monocytes and in substantia nigra from affected individuals and controls. We confirmed previous findings of a paradoxically longer telomere length in blood from PD patients, but found no difference in telomere length in substantia nigra. Confounding factors provide a likely explanation for the findings in blood, and possibly the reduced frequency of cigarette smoking in PD patients. We conclude that telomere shortening is unlikely to be involved in the pathogenesis of PD.
PMCID: PMC4034165  PMID: 21794951
14.  Single-Cell Expression Profiling of Dopaminergic Neurons Combined with Association Analysis Identifies Pyridoxal Kinase as Parkinson’s Disease Gene 
Annals of neurology  2009;66(6):792-798.
The etiology of Parkinson disease (PD) is complex and multifactorial, with hereditary and environmental factors contributing. Monogenic forms have provided molecular clues to disease mechanisms but genetic modifiers of idiopathic PD are still to be determined.
We carried out whole-genome expression profiling of isolated human substantia nigra (SN) neurons from patients with PD vs. controls followed by association analysis of tagging single-nucleotide polymorphisms (SNPs) in differentially regulated genes. Association was investigated in a German PD sample and confirmed in Italian and British cohorts.
We identified four differentially expressed genes located in PD candidate pathways, ie, MTND2 (mitochondrial, p = 7.14 × 10−7), PDXK (vitamin B6/dopamine metabolism, p = 3.27 × 10−6), SRGAP3 (axon guidance, p = 5.65 × 10−6), and TRAPPC4 (vesicle transport, p = 5.81 × 10−6). We identified a DNA variant (rs2010795) in PDXK associated with an increased risk of PD in the German cohort (p = 0.00032). This association was confirmed in the British (p = 0.028) and Italian (p = 0.0025) cohorts individually and reached a combined value of p = 1.2 × 10−7 (odds ratio [OR], 1.3; 95% confidence interval [CI], 1.18–1.44).
We provide an example of how microgenomic genome-wide expression studies in combination with association analysis can aid to identify genetic modifiers in neurodegenerative disorders. The detection of a genetic variant in PDXK, together with evidence accumulating from clinical studies, emphasize the impact of vitamin B6 status and metabolism on disease risk and therapy in PD.
PMCID: PMC4034432  PMID: 20035503
15.  Subthalamic deep brain stimulation in Parkinson׳s disease has no significant effect on perceptual timing in the hundreds of milliseconds range 
Neuropsychologia  2014;57(100):29-37.
Bilateral, high-frequency stimulation of the basal ganglia (STN-DBS) is in widespread use for the treatment of the motor symptoms of Parkinson׳s disease (PD). We present here the first psychophysical investigation of the effect of STN-DBS upon perceptual timing in the hundreds of milliseconds range, with both duration-based (absolute) and beat-based (relative) tasks; 13 patients with PD were assessed with their STN-DBS ‘on’, ‘off’, and then ‘on’ again.
Paired parametric analyses revealed no statistically significant differences for any task according to DBS status. We demonstrate, from the examination of confidence intervals, that any functionally relevant effect of STN-DBS on relative perceptual timing is statistically unlikely. For absolute, duration-based timing, we demonstrate that the activation of STN-DBS may either worsen performance or have no effect, but that it is unlikely to lead to significant improvement.
Although these results are negative they have important implications for our understanding of perceptual timing and its relationship to motor functions within the timing network of the brain. They imply that the mechanisms involved in the perceptual processing of temporal information are likely to be functionally independent from those that underpin movement. Further, they suggest that the connections between STN and the subtantia nigra and globus pallidus are unlikely to be critical to beat-based perceptual timing.
Graphical abstract
Paired difference in performance thresholds according to DBS status. The first and third measures within each triplet show performance for that run with DBS ‘on’ compared to that with DBS ‘off’; values greater than zero denote poorer performance with DBS ‘on’, while those less than zero denote poorer performance with DBS ‘off’. The middle measure shows the difference in performance between the two runs with DBS ‘on’. Error bars denote confidence intervals.
•We assessed the effect of STN-DBS on both duration- and beat-based perceptual timing.•DBS activation did not profoundly affect beat-based perceptual timing.•An effect of DBS on duration-based timing was not demonstrated but cannot be excluded.•Connections between STN and cerebellum are unlikely to be critical to perceptual timing.
PMCID: PMC4022837  PMID: 24613477
Perceptual timing; Parkinson׳s disease; Subthalamic nucleus; Deep brain stimulation
16.  A pathway-based analysis provides additional support for an immune-related genetic susceptibility to Parkinson's disease 
Holmans, Peter | Moskvina, Valentina | Jones, Lesley | Sharma, Manu | Vedernikov, Alexey | Buchel, Finja | Sadd, Mohamad | Bras, Jose M. | Bettella, Francesco | Nicolaou, Nayia | Simón-Sánchez, Javier | Mittag, Florian | Gibbs, J. Raphael | Schulte, Claudia | Durr, Alexandra | Guerreiro, Rita | Hernandez, Dena | Brice, Alexis | Stefánsson, Hreinn | Majamaa, Kari | Gasser, Thomas | Heutink, Peter | Wood, Nicholas W. | Martinez, Maria | Singleton, Andrew B. | Nalls, Michael A. | Hardy, John | Morris, Huw R. | Williams, Nigel M. | Arepalli, Sampath | Barker, Roger | Barrett, Jeffrey | Ben-Shlomo, Yoav | Berendse, Henk W. | Berg, Daniela | Bhatia, Kailash | de Bie, Rob M.A. | Biffi, Alessandro | Bloem, Bas | Brice, Alexis | Bochdanovits, Zoltan | Bonin, Michael | Bras, Jose M. | Brockmann, Kathrin | Brooks, Janet | Burn, David J. | Charlesworth, Gavin | Chen, Honglei | Chinnery, Patrick F. | Chong, Sean | Clarke, Carl E. | Cookson, Mark R. | Cooper, Jonathan M. | Corvol, Jen-Christophe | Counsell, Carl | Damier, Philippe | Dartigues, Jean Francois | Deloukas, Panagiotis | Deuschl, Günther | Dexter, David T. | van Dijk, Karin D. | Dillman, Allissa | Durif, Frank | Durr, Alexandra | Edkins, Sarah | Evans, Jonathan R. | Foltynie, Thomas | Gao, Jianjun | Gardner, Michelle | Gasser, Thomas | Gibbs, J. Raphael | Goate, Alison | Gray, Emma | Guerreiro, Rita | Gústafsson, Ómar | Hardy, John | Harris, Clare | Hernandez, Dena G. | Heutink, Peter | van Hilten, Jacobus J. | Hofman, Albert | Hollenbeck, Albert | Holmans, Peter | Holton, Janice | Hu, Michele | Huber, Heiko | Hudson, Gavin | Hunt, Sarah E. | Huttenlocher, Johanna | Illig, Thomas | Langford, Cordelia | Lees, Andrew | Lesage, Suzanne | Lichtner, Peter | Limousin, Patricia | Lopez, Grisel | Lorenz, Delia | Martinez, Maria | McNeill, Alisdair | Moorby, Catriona | Moore, Matthew | Morris, Huw | Morrison, Karen E. | Moskvina, Valentina | Mudanohwo, Ese | Nalls, Michael A. | Pearson, Justin | Perlmutter, Joel S. | Pétursson, Hjörvar | Plagnol, Vincent | Pollak, Pierre | Post, Bart | Potter, Simon | Ravina, Bernard | Revesz, Tamas | Riess, Olaf | Rivadeneira, Fernando | Rizzu, Patrizia | Ryten, Mina | Saad, Mohamad | Sawcer, Stephen | Schapira, Anthony | Scheffer, Hans | Sharma, Manu | Shaw, Karen | Sheerin, Una-Marie | Shoulson, Ira | Schulte, Claudia | Sidransky, Ellen | Simón-Sánchez, Javier | Singleton, Andrew B. | Smith, Colin | Stefánsson, Hreinn | Stefánsson, Kári | Steinberg, Stacy | Stockton, Joanna D. | Sveinbjornsdottir, Sigurlaug | Talbot, Kevin | Tanner, Carlie M. | Tashakkori-Ghanbaria, Avazeh | Tison, François | Trabzuni, Daniah | Traynor, Bryan J. | Uitterlinden, André G. | Velseboer, Daan | Vidailhet, Marie | Walker, Robert | van de Warrenburg, Bart | Wickremaratchi, Mirdhu | Williams, Nigel | Williams-Gray, Caroline H. | Winder-Rhodes, Sophie | Wood, Nicholas
Human Molecular Genetics  2012;22(5):1039-1049.
Parkinson's disease (PD) is the second most common neurodegenerative disease affecting 1–2% in people >60 and 3–4% in people >80. Genome-wide association (GWA) studies have now implicated significant evidence for association in at least 18 genomic regions. We have studied a large PD-meta analysis and identified a significant excess of SNPs (P < 1 × 10−16) that are associated with PD but fall short of the genome-wide significance threshold. This result was independent of variants at the 18 previously implicated regions and implies the presence of additional polygenic risk alleles. To understand how these loci increase risk of PD, we applied a pathway-based analysis, testing for biological functions that were significantly enriched for genes containing variants associated with PD. Analysing two independent GWA studies, we identified that both had a significant excess in the number of functional categories enriched for PD-associated genes (minimum P = 0.014 and P = 0.006, respectively). Moreover, 58 categories were significantly enriched for associated genes in both GWA studies (P < 0.001), implicating genes involved in the ‘regulation of leucocyte/lymphocyte activity’ and also ‘cytokine-mediated signalling’ as conferring an increased susceptibility to PD. These results were unaltered by the exclusion of all 178 genes that were present at the 18 genomic regions previously reported to be strongly associated with PD (including the HLA locus). Our findings, therefore, provide independent support to the strong association signal at the HLA locus and imply that the immune-related genetic susceptibility to PD is likely to be more widespread in the genome than previously appreciated.
PMCID: PMC3561909  PMID: 23223016
17.  The basal ganglia in perceptual timing: Timing performance in Multiple System Atrophy and Huntington's disease☆ 
Neuropsychologia  2014;52(100):73-81.
The timing of perceptual events depends on an anatomically and functionally connected network comprising basal ganglia, cerebellum, pre-frontal cortex and supplementary motor area. Recent studies demonstrate the cerebellum to be involved in absolute, duration-based timing, but not in relative timing based on a regular beat. Conversely, functional involvement of the striatum is observed in relative timing, but its role in absolute timing is unclear.
This work tests the specific role of the basal ganglia in the perceptual timing of auditory events. It aims to distinguish the hypothesised unified model of time perception (Teki, Grube, & Griffiths, 2012), in which the striatum is a mandatory component for all timing tasks, from a modular system in which they subserve relative timing, with absolute timing processed by the cerebellum.
Test groups comprised individuals with Multiple System Atrophy, a disorder in which similar pathology can produce clinical deficits associated with dysfunction of the cerebellum (MSA-C, n=8) or striatum (MSA-P, n=10), and early symptomatic Huntington's disease (HD, n=14). Individuals with chronic autoimmune peripheral neuropathy (n=11) acted as controls.
Six adaptive tasks were carried out to assess perceptual thresholds for absolute timing through duration discrimination for sub- and supra-second time intervals, and relative timing through the detection of beat-based regularity and irregularity, detection of a delay within an isochronous sequence, and the discrimination of sequences with metrical structure.
All three patient groups exhibited impairments in performance in comparison with the control group for all tasks, and severity of impairment was significantly correlated with disease progression. No differences were demonstrated between MSA-C and MSA-P, and the most severe impairments were observed in those with HD.
The data support an obligatory role for the basal ganglia in all tested timing tasks, both absolute and relative, as predicted by the unified model. The results are not compatible with models of a brain timing network based upon independent modules.
Graphical abstract
Ninety five percent confidence intervals for mean group performance by task. Var: sub-second variable-interval discrimination. Sup: supra-second variable-interval discrimination. Pul: detection of regularity (pulse or beat) within an irregular sequence. Iso: detection of deviation from isochrony. Irr: detection of irregularity within a regular sequence. Met: detection of distortion of a sequence with strong metrical structure.
•Patients with basal ganglia disease undertook a battery of perceptual timing tasks.•All patients displayed poorer performance than neurological control participants.•Performance in Huntington's disease was worse than Multiple System Atrophy.•Poorer performance was significantly correlated with disease progression.•These findings support the hypothesised unified model of time perception.
PMCID: PMC3905186  PMID: 24135486
Perceptual timing; Beat; Basal ganglia; Multiple System Atrophy; Huntington's disease
18.  Prevalence and pattern of perceived intelligibility changes in Parkinson's disease 
Changes to spoken communication are inevitable in Parkinson's disease (PD). It remains unclear what consequences changes have for intelligibility of speech.
To establish the prevalence of impaired speech intelligibility in people with PD and the relationship of intelligibility decline to indicators of disease progression.
125 speakers with PD and age matched unaffected controls completed a diagnostic intelligibility test and described how to carry out a common daily activity in an “off drug” state. Listeners unfamiliar with dysarthric speech evaluated responses.
69.6% (n = 87) of people with PD fell below the control mean of unaffected speakers (n = 40), 51.2% (n = 64) by more than −1 SD below. 48% (n = 60) were perceived as worse than the lowest unaffected speaker for how disordered speech sounded. 38% (n = 47) placed speech changes among their top four concerns regarding their PD. Intelligibility level did not correlate significantly with age or disease duration and only weakly with stage and severity of PD. There were no significant differences between participants with tremor dominant versus postural instability/gait disorder motor phenotypes of PD.
Speech intelligibility is significantly reduced in PD; it can be among the main concerns of people with PD, but it is not dependent on disease severity, duration or motor phenotype. Patients' own perceptions of the extent of change do not necessarily reflect objective measures.
PMCID: PMC2117612  PMID: 17400592
19.  Cholinesterase inhibitor use does not significantly influence the ability of 123I‐FP‐CIT imaging to distinguish Alzheimer's disease from dementia with Lewy bodies 
123I‐labelled 2β‐carbomethoxy‐3β‐(4‐iodophenyl)‐N‐(3‐fluoropropyl) nortropane (123I‐FP‐CIT) imaging is a diagnostic tool to help differentiate dementia with Lewy bodies (DLB) from Alzheimer's disease (AD). However, in animals, cholinesterase inhibitors (ChEi) have been reported to reduce radioligand binding to the striatal dopamine transporter. As ChEi are frequently used in people with dementia, it is important to determine whether their use affects 123I‐FP‐CIT uptake in the striatum.
To clarify whether chronic ChEi therapy modulates striatal dopamine transporter binding measured by 123I‐FP‐CIT in patients with AD, DLB and Parkinson's disease with dementia (PDD).
Cross sectional study in 99 patients with AD (nine on ChEi, 25 not on ChEi), DLB (nine on ChEi, 19 not on ChEi) and PDD (six on ChEi, 31 not on ChEi) comparing 123I‐FP‐CIT striatal binding (caudate, anterior and posterior putamen) in patients receiving compared with those not receiving ChEi, correcting for key clinical variables including diagnosis, age, sex, Mini‐Mental State Examination score, severity of parkinsonism and concurrent antidepressant use.
As previously described, 123I‐FP‐CIT striatal uptake was lower in DLB and PDD subjects compared with those with AD. Median duration of ChEi use was 180 days. 123I‐FP‐CIT uptake was not significantly reduced in subjects receiving ChEi compared those not receiving ChEi (mean percentage reduction: AD 4.3%; DLB 0.7%; PDD 6.1%; p = 0.40). ChEi use did not differentially affect striatal 123FP‐CIT uptake between patient groups (p = 0.83).
Use of ChEi does not significantly influence the ability of 123I‐FP‐CIT imaging to distinguish AD from DLB.
PMCID: PMC2117542  PMID: 17299017
20.  Sex and Parkinson's disease: a world of difference? 
Do women with Parkinson's disease have a more benign phenotype?
PMCID: PMC2117743  PMID: 17635975
21.  Cholinergic dysfunction contributes to gait disturbance in early Parkinson’s disease 
Brain  2012;135(9):2779-2788.
Gait disturbance is an early feature in Parkinson’s disease. Its pathophysiology is poorly understood; however, cholinergic dysfunction may be a non-dopaminergic contributor to gait. Short-latency afferent inhibition is a surrogate measure of cholinergic activity, allowing the contribution of cholinergic dysfunction to gait to be evaluated. We hypothesized that short-latency afferent inhibition would be an independent predictor of gait dysfunction in early Parkinson’s disease. Twenty-two participants with Parkinson’s disease and 22 age-matched control subjects took part in the study. Gait was measured objectively using an instrumented walkway (GAITRite), and subjects were asked to walk at their preferred speed for 2 min around a 25-m circuit. Spatiotemporal characteristics (speed, stride length, stride time and step width) and gait dynamics (variability described as the within subject standard deviation of: speed, stride time, stride length and step width) were determined. Short-latency afferent inhibition was measured by conditioning motor evoked potentials, elicited by transcranial magnetic stimulation of the motor cortex, with electrical stimuli delivered to the contralateral median nerve at intervals ranging from N20 (predetermined) to N20 + 4 ms. Short-latency afferent inhibition was determined as the percentage difference between test and conditioned response for all intervals and was described as the group mean. Participants were optimally medicated at the time of testing. Participants with Parkinson’s disease had significantly reduced gait speed (P = 0.002), stride length (P = 0.008) and stride time standard deviation (P = 0.001). Short-latency afferent inhibition was also significantly reduced in participants with Parkinson’s disease (P = 0.004). In participants with Parkinson’s disease, but not control subjects, significant associations were found between gait speed, short-latency afferent inhibition, age and postural instability and gait disorder score (Movement Disorders Society Unified Parkinson’s Disease Rating Scale) and attention, whereas global cognition and depression were marginally significant. No other gait variables were associated with short-latency afferent inhibition. A multiple hierarchical regression model explored the contribution of short-latency afferent inhibition to gait speed, controlling for age, posture and gait symptoms (Postural Instability and Gait Disorder score—Movement Disorders Society Unified Parkinson’s Disease Rating Scale), attention and depression. Regression analysis in participants with Parkinson’s disease showed that reduced short-latency afferent inhibition was an independent predictor of slower gait speed, explaining 37% of variability. The final model explained 72% of variability in gait speed with only short-latency afferent inhibition and attention emerging as independent determinants. The results suggest that cholinergic dysfunction may be an important and early contributor to gait dysfunction in Parkinson’s disease. The findings also point to the contribution of non-motor mechanisms to gait dysfunction. Our study provides new insights into underlying mechanisms of non-dopaminergic gait dysfunction, and may help to direct future therapeutic approaches.
PMCID: PMC3437031  PMID: 22961550
Parkinson’s disease; gait; short-latency afferent inhibition; cholinergic dysfunction; attention
22.  Parkinson's Disease: The Quintessential Neuropsychiatric Disorder 
Although diagnosed by characteristic motor features, Parkinson's disease may be preceded, and is frequently accompanied by, a wide range of cognitive and neuropsychiatric features. In addition to the most commonly studied disorders of dementia, depression, and psychosis, other relatively common and clinically significant psychiatric complications include impulse control disorders, anxiety symptoms, disorders of sleep and wakefulness, and apathy. These problems may be underrecognized and are frequently undertreated. The emergent focus on nonmotor aspects of Parkinson's disease over the past quarter of a century is highlighted by a nonlinear increase in the number of articles published devoted to this topic. Although the development of newer antidepressants, atypical antipsychotics, and cholinesterase inhibitors in recent years has had a positive benefit on the management of these troublesome and distressing symptoms, responses are frequently suboptimal, and this remains an area of major unmet therapeutic need.
PMCID: PMC3513835  PMID: 21626547
Parkinson's; dementia; neuropsychiatric; depression; psychosis
23.  Tau acts as an independent genetic risk factor in pathologically proven PD 
Neurobiology of Aging  2012;33(4):838.e7-838.e11.
MAPT has been repeatedly linked with Parkinson's disease (PD) in association studies. Although tau deposition may be seen in PD, its relevance to the pathogenesis of the condition remains unclear. The presence of tau-positive inclusions is, however, the defining feature of progressive supranuclear palsy (PSP), which may often be clinically misdiagnosed as idiopathic PD. On a genetic level, variants in MAPT are the strongest risk factor for PSP. These facts raise the question whether the MAPT association in PD results from contamination with unrecognized cases of PSP. Using only neuropathologically proven PD, we show that the MAPT association remains and is independent of the PSP Association.
PMCID: PMC3629571  PMID: 22221882
Genetics; Association study; Parkinson's disease; MAPT; Tau; Progressive supranuclear palsy; PD; PSP
25.  Huntington CAG repeat size does not modify onset age in familial Parkinson’s disease: The GenePD Study 
The ATP/ADP ratio reflects mitochondrial function and has been reported to be influenced by the size of the Huntington disease gene (HD) repeat. Impaired mitochondrial function has long been implicated in the pathogenesis of Parkinson’s disease (PD) and therefore, we evaluated the relationship of the HD CAG repeat size to PD onset age in a large sample of familial PD cases. PD affected siblings (n=495) with known onset ages from 248 families, were genotyped for the HD CAG repeat. Genotyping failed in 11 cases leaving 484 for analysis, including 35 LRRK2 carriers. All cases had HD CAG repeats (range 15 to 34) below the clinical range for HD, although 5.2 percent of the sample (n=25) had repeats in the intermediate range (the intermediate range lower limit=27; upper limit=35 repeats), suggesting that the prevalence of intermediate allele carriers in the general population is significant. No relation between the HD CAG repeat size and the age at onset for PD was found in this sample of familial PD.
PMCID: PMC2655323  PMID: 18649400
Parkinson’s disease; Huntington’s disease; CAG repeat; onset age; genetics; mitochondria

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