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Figure 1.
Family Tree and Neuropathology Findings
Family Tree and Neuropathology Findings

A, The arrowhead depicts the proband. Information has been omitted for deidentification purposes. B, Representative images of α-synuclein immunoreactive inclusion stains within the substantia nigra (a), locus coeulus (b), nucleus basalis of Meynert (c), and transentorhinal cortex (d). Severe neuritic α-synuclein deposition is shown in the cornu ammonis 2 region of the hippocampus at low and high magnification (e and f). α-Synuclein coiled bodies are shown in the white matter of the cerebellum (g and h). Sparse AT8 (phospho-tau, Ser 202, and Thr205 stains) immunoreactive neurofibrillary tangles were observed in the transentorhinal cortex (i and j). Scale bars represent 50 μm.

Figure 2.
Genetic Findings
Genetic Findings

A, Multiplex ligation–dependent probe amplification results depicting the duplication. B, Minimum duplicated region as identified by the comparative genomic hybridization array (chr4:88349207-94751141, human build 37). C, Minimum duplicated region as identified by ImmunoChip (chr4: 88231429-94816144 human build 37) with an increased logR ratio and probes forming 4 distinct genotype clusters.21 The region depicted in the figure is chr4: 83666791-97713411 (human build 37). D, Genes included within the minimum duplicated region (chr4:88349207-94751141, human build 37) as identified by the comparative genomic hybridization array. E, Break point regions and repetitive sequences identified through the University of California, Santa Cruz RepeatMasker (http://genome.ucsc.edu/). The upper panel depicts the centromeric (chr4:88249207-88349207) and the lower panel depicts the telomeric (chr4: 94751141-94851141) break point regions. F, Comparison of the length of the duplicated/triplicated region between our case and published cases (band sizes are approximate). Sizes represent minimum length based on human genome build 36. G, Location of break points. The height of peak corresponds to the number of cases with a break point in the particular region. Break point location could correspond to regions of recombination hotspots.22,23 The case reported by Garraux et al11 was excluded from both images.

Table 1.  
Genes Included in the Duplicated Region in Patient III:1a
Genes Included in the Duplicated Region in Patient III:1a
Table 2.  
Demographic and Clinical Characteristics of Study Sample by Disease Status
Demographic and Clinical Characteristics of Study Sample by Disease Status
Table 3.  
Estimates for Univariable and Multivariable Modelsa
Estimates for Univariable and Multivariable Modelsa
1.
Spillantini  MG, Schmidt  ML, Lee  VM, Trojanowski  JQ, Jakes  R, Goedert  M.  Alpha-synuclein in Lewy bodies. Nature. 1997;388(6645):839-840.
PubMedArticle
2.
Polymeropoulos  MH, Lavedan  C, Leroy  E,  et al.  Mutation in the alpha-synuclein gene identified in families with Parkinson’s disease. Science. 1997;276(5321):2045-2047.
PubMedArticle
3.
Singleton  AB, Farrer  M, Johnson  J,  et al.  alpha-Synuclein locus triplication causes Parkinson’s disease. Science. 2003;302(5646):841.
PubMedArticle
4.
Ibáñez  P, Bonnet  AM, Débarges  B,  et al.  Causal relation between alpha-synuclein gene duplication and familial Parkinson’s disease. Lancet. 2004;364(9440):1169-1171.
PubMedArticle
5.
Gwinn  K, Devine  MJ, Jin  LW,  et al.  Clinical features, with video documentation, of the original familial lewy body parkinsonism caused by α-synuclein triplication (Iowa kindred). Mov Disord. 2011;26(11):2134-2136.
PubMedArticle
6.
Kara  E, Ling  H, Pittman  AM,  et al.  The MAPT p.A152T variant is a risk factor associated with tauopathies with atypical clinical and neuropathological features. Neurobiol Aging. 2012;33(9):e7, e14.
PubMedArticle
7.
Schouten  JP, McElgunn  CJ, Waaijer  R, Zwijnenburg  D, Diepvens  F, Pals  G.  Relative quantification of 40 nucleic acid sequences by multiplex ligation-dependent probe amplification. Nucleic Acids Res. 2002;30(12):e57.
PubMedArticle
8.
Plagnol  V, Nalls  MA, Bras  JM,  et al; International Parkinson’s Disease Genomics Consortium (IPDGC); Wellcome Trust Case Control Consortium 2 (WTCCC2).  A two-stage meta-analysis identifies several new loci for Parkinson’s disease. PLoS Genet. 2011;7(6):e1002142.
PubMedArticle
9.
Jostins  L, Ripke  S, Weersma  RK,  et al; International IBD Genetics Consortium (IIBDGC).  Host-microbe interactions have shaped the genetic architecture of inflammatory bowel disease. Nature. 2012;491(7422):119-124.
PubMedArticle
10.
Faraco  J, Lin  L, Kornum  BR,  et al.  ImmunoChip study implicates antigen presentation to T cells in narcolepsy. PLoS Genet. 2013;9(2):e1003270.
PubMedArticle
11.
Garraux  G, Caberg  JH, Vanbellinghen  JF,  et al.  Partial trisomy 4q associated with young-onset dopa-responsive parkinsonism. Arch Neurol. 2012;69(3):398-400.
PubMedArticle
12.
Williams  RL.  A note on robust variance estimation for cluster-correlated data. Biometrics. 2000;56(2):645-646.
PubMedArticle
13.
Harrell  FE  Jr, Margolis  PA, Gove  S,  et al; WHO/ARI Young Infant Multicentre Study Group.  Development of a clinical prediction model for an ordinal outcome: the World Health Organization Multicentre Study of Clinical Signs and Etiological agents of Pneumonia, Sepsis and Meningitis in Young Infants. Stat Med. 1998;17(8):909-944.
PubMedArticle
14.
Austin  PC.  Estimating multilevel logistic regression models when the number of clusters is low: a comparison of different statistical software procedures. Int J Biostat. 2010;6(1):16.
PubMed
15.
Chirwa  ED, Griffiths  PL, Maleta  K, Norris  SA, Cameron  N.  Multi-level modelling of longitudinal child growth data from the Birth-to-Twenty Cohort: a comparison of growth models. Ann Hum Biol. 2014;41(2):166-177.
PubMedArticle
16.
StataCorp. Stata Statistical Software: Release 12. College Station, TX: StataCorp LP; 2011.
17.
Team RCR. A language and environment for statistical computing. R Foundation for Statistical Computing, Vienna, Austria. http://www.r-project.org/. 2013. Accessed June 2014.
18.
Wickham  H. ggplot2: Elegant Graphics for Data Analysis. New York, NY: Springer; 2009.
19.
Braak  H, Alafuzoff  I, Arzberger  T, Kretzschmar  H, Del Tredici  K.  Staging of Alzheimer disease-associated neurofibrillary pathology using paraffin sections and immunocytochemistry. Acta Neuropathol. 2006;112(4):389-404.
PubMedArticle
20.
McKeith  IG, Dickson  DW, Lowe  J,  et al; Consortium on DLB.  Diagnosis and management of dementia with Lewy bodies: third report of the DLB Consortium. Neurology. 2005;65(12):1863-1872.
PubMedArticle
21.
Simon-Sanchez  J, Scholz  S, Fung  HC,  et al.  Genome-wide SNP assay reveals structural genomic variation, extended homozygosity and cell-line induced alterations in normal individuals. Hum Mol Genet. 2007;16(1):1-14.
PubMedArticle
22.
Nalls  MA, Plagnol  V, Hernandez  DG,  et al; International Parkinson Disease Genomics Consortium.  Imputation of sequence variants for identification of genetic risks for Parkinson’s disease: a meta-analysis of genome-wide association studies. Lancet. 2011;377(9766):641-649.
PubMedArticle
23.
Simón-Sánchez  J, Schulte  C, Bras  JM,  et al.  Genome-wide association study reveals genetic risk underlying Parkinson’s disease. Nat Genet. 2009;41(12):1308-1312.
PubMedArticle
24.
Zhang  X, Zhao  J, Li  C,  et al.  DSPP mutation in dentinogenesis imperfecta Shields type II. Nat Genet. 2001;27(2):151-152.
PubMedArticle
25.
Xiao  S, Yu  C, Chou  X,  et al.  Dentinogenesis imperfecta 1 with or without progressive hearing loss is associated with distinct mutations in DSPP. Nat Genet. 2001;27(2):201-204.
PubMedArticle
26.
Lorenz-Depiereux  B, Bastepe  M, Benet-Pagès  A,  et al.  DMP1 mutations in autosomal recessive hypophosphatemia implicate a bone matrix protein in the regulation of phosphate homeostasis. Nat Genet. 2006;38(11):1248-1250.
PubMedArticle
27.
Mochizuki  T, Wu  G, Hayashi  T,  et al.  PKD2, a gene for polycystic kidney disease that encodes an integral membrane protein. Science. 1996;272(5266):1339-1342.
PubMedArticle
28.
Hills  LB, Masri  A, Konno  K,  et al.  Deletions in GRID2 lead to a recessive syndrome of cerebellar ataxia and tonic upgaze in humans. Neurology. 2013;81(16):1378-1386.
PubMedArticle
29.
Hernandez  DG, Nalls  MA, Ylikotila  P,  et al.  Genome wide assessment of young onset Parkinson’s disease from Finland. PLoS One. 2012;7(7):e41859.
PubMedArticle
30.
Kara  E, Xiromerisiou  G, Spanaki  C,  et al.  Assessment of Parkinson’s disease risk loci in Greece. Neurobiol Aging. 2014;35(2):e9-e16, e16.
PubMedArticle
31.
Elia  AE, Petrucci  S, Fasano  A,  et al.  Alpha-synuclein gene duplication: marked intrafamilial variability in two novel pedigrees. Mov Disord. 2013;28(6):813-817.
PubMedArticle
32.
Ikeuchi  T, Kakita  A, Shiga  A,  et al.  Patients homozygous and heterozygous for SNCA duplication in a family with parkinsonism and dementia. Arch Neurol. 2008;65(4):514-519.
PubMedArticle
33.
Wakabayashi  K, Hayashi  S, Ishikawa  A,  et al.  Autosomal dominant diffuse Lewy body disease. Acta Neuropathol. 1998;96(2):207-210.
PubMedArticle
34.
Nishioka  K, Hayashi  S, Farrer  MJ,  et al.  Clinical heterogeneity of alpha-synuclein gene duplication in Parkinson’s disease. Ann Neurol. 2006;59(2):298-309.
PubMedArticle
35.
Obi  T, Nishioka  K, Ross  OA,  et al.  Clinicopathologic study of a SNCA gene duplication patient with Parkinson disease and dementia. Neurology. 2008;70(3):238-241.
PubMedArticle
36.
Ross  OA, Braithwaite  AT, Skipper  LM,  et al.  Genomic investigation of alpha-synuclein multiplication and parkinsonism. Ann Neurol. 2008;63(6):743-750.
PubMedArticle
37.
Nishioka  K, Ross  OA, Ishii  K,  et al.  Expanding the clinical phenotype of SNCA duplication carriers. Mov Disord. 2009;24(12):1811-1819.
PubMedArticle
38.
Ibáñez  P, Lesage  S, Janin  S,  et al; French Parkinson’s Disease Genetics Study Group.  Alpha-synuclein gene rearrangements in dominantly inherited parkinsonism: frequency, phenotype, and mechanisms. Arch Neurol. 2009;66(1):102-108.
PubMedArticle
39.
Ivics  Z, Izsvák  Z.  Repetitive elements and genome instability. Semin Cancer Biol. 2010;20(4):197-199.
PubMedArticle
40.
Rozier  L, El-Achkar  E, Apiou  F, Debatisse  M.  Characterization of a conserved aphidicolin-sensitive common fragile site at human 4q22 and mouse 6C1: possible association with an inherited disease and cancer. Oncogene. 2004;23(41):6872-6880.
PubMedArticle
41.
Fungtammasan  A, Walsh  E, Chiaromonte  F, Eckert  KA, Makova  KD.  A genome-wide analysis of common fragile sites: what features determine chromosomal instability in the human genome? Genome Res. 2012;22(6):993-1005.
PubMedArticle
42.
Itokawa  K, Sekine  T, Funayama  M,  et al.  A case of α-synuclein gene duplication presenting with head-shaking movements. Mov Disord. 2013;28(3):384-387.
PubMedArticle
43.
Guo  JL, Covell  DJ, Daniels  JP,  et al.  Distinct α-synuclein strains differentially promote tau inclusions in neurons. Cell. 2013;154(1):103-117.
PubMedArticle
44.
Bonett  DG, Right  TAW.  Sample size requirements for estimating pearson, kendall, and spearman correlations. Psychometrika.2000;65(1):23-28. doi: 10.1007/BF02294183Article
45.
Hsieh  FY.  Sample size tables for logistic regression. Stat Med. 1989;8(7):795-802.
PubMedArticle
46.
Wooten  GF, Currie  LJ, Bovbjerg  VE, Lee  JK, Patrie  J.  Are men at greater risk for Parkinson’s disease than women? J Neurol Neurosurg Psychiatry. 2004;75(4):637-639.
PubMedArticle
47.
Taylor  KS, Cook  JA, Counsell  CE.  Heterogeneity in male to female risk for Parkinson’s disease. J Neurol Neurosurg Psychiatry. 2007;78(8):905-906.
PubMedArticle
48.
Spencer  CC, Plagnol  V, Strange  A,  et al; UK Parkinson’s Disease Consortium; Wellcome Trust Case Control Consortium 2.  Dissection of the genetics of Parkinson’s disease identifies an additional association 5′ of SNCA and multiple associated haplotypes at 17q21. Hum Mol Genet. 2011;20(2):345-353.
PubMedArticle
49.
Rhinn  H, Qiang  L, Yamashita  T,  et al.  Alternative α-synuclein transcript usage as a convergent mechanism in Parkinson’s disease pathology. Nat Commun. 2012;3:1084.
PubMedArticle
50.
Proukakis  C, Houlden  H, Schapira  AH.  Somatic alpha-synuclein mutations in Parkinson’s disease: hypothesis and preliminary data. Mov Disord. 2013;28(6):705-712.
PubMedArticle
51.
Baranzini  SE, Mudge  J, van Velkinburgh  JC,  et al.  Genome, epigenome and RNA sequences of monozygotic twins discordant for multiple sclerosis. Nature. 2010;464(7293):1351-1356.
PubMedArticle
52.
Xiromerisiou  G, Houlden  H, Sailer  A, Silveira-Moriyama  L, Hardy  J, Lees  AJ.  Identical twins with Leucine rich repeat kinase type 2 mutations discordant for Parkinson’s disease. Mov Disord. 2012;27(10):1323.
PubMedArticle
Original Investigation
September 2014

A 6.4 Mb Duplication of the α-Synuclein Locus Causing Frontotemporal Dementia and ParkinsonismPhenotype-Genotype Correlations

Author Affiliations
  • 1Department of Molecular Neuroscience, UCL Institute of Neurology, London, United Kingdom
  • 2The Queen Square Brain Bank, UCL Institute of Neurology, London, United Kingdom
  • 3Department of Clinical Neuroscience, UCL Institute of Neurology, London, United Kingdom
  • 4Department of Neurology, Frenchay Hospital, Bristol, United Kingdom
  • 5Department of Neuropathology, Frenchay Hospital, Bristol, United Kingdom
  • 6Biomedical Research Centre, UCL, London, United Kingdom
  • 7Education Unit, UCL Institute of Neurology, Queen Square, London, United Kingdom
  • 8Laboratory of Neurogenetics, National Institute on Aging, National Institutes of Health, Bethesda, Maryland
  • 9Department of Academic Hematology, Royal Free Campus, UCL, London, United Kingdom
  • 10Sobell Department of Motor Neuroscience and Movement Disorders, UCL Institute of Neurology, London, United Kingdom
  • 11MRC Centre for Neuromuscular Diseases, UCL Institute of Neurology, London, United Kingdom
JAMA Neurol. 2014;71(9):1162-1171. doi:10.1001/jamaneurol.2014.994
Abstract

Importance  α-Synuclein (SNCA) locus duplications are associated with variable clinical features and reduced penetrance but the reasons underlying this variability are unknown.

Objectives  To report a novel family carrying a heterozygous 6.4 Mb duplication of the SNCA locus with an atypical clinical presentation strongly reminiscent of frontotemporal dementia and late-onset pallidopyramidal syndromes and study phenotype-genotype correlations in SNCA locus duplications.

Design, Setting, and Participants  We report the clinical and neuropathologic features of a family carrying a 6.4 Mb duplication of the SNCA locus. To identify candidate disease modifiers, we completed a genetic analysis of the family and conducted statistical analysis on previously published cases carrying SNCA locus duplications using regression modeling with robust standard errors to account for clustering at the family level.

Main Outcomes and Measures  We assessed whether length of the SNCA locus duplication influences disease penetrance and severity and whether extraduplication factors have a disease-modifying role.

Results  We identified a large 6.4 Mb duplication of the SNCA locus in this family. Neuropathological analysis showed extensive α-synuclein pathology with minimal phospho-tau pathology. Genetic analysis showed an increased burden of Parkinson disease–related risk factors and the disease-predisposing H1/H1 microtubule-associated protein tau haplotype. Statistical analysis of previously published cases suggested there is a trend toward increasing disease severity and disease penetrance with increasing duplication size. The corresponding odds ratios from the univariable analyses were 1.17 (95% CI, 0.81-1.68) and 1.34 (95% CI, 0.78-2.31), respectively. Sex was significantly associated with both disease risk and severity; men compared with women had increased disease risk and severity and the corresponding odds ratios from the univariable analyses were 8.36 (95% CI, 1.97-35.42) and 5.55 (95% CI, 1.39-22.22), respectively.

Conclusions and Relevance  These findings further expand the phenotypic spectrum of SNCA locus duplications. Increased dosage of genes located within the duplicated region probably cannot increase disease risk and disease severity without the contribution of additional risk factors. Identification of disease modifiers accounting for the substantial phenotypic heterogeneity of patients with SNCA locus duplications could provide insight into molecular events involved in α-synuclein aggregation.

Introduction

α-Synuclein is a protein central to the pathogenesis of Parkinson disease (PD). This has been illustrated by the identification of α-synuclein as the principal component of Lewy bodies (LBs),1 the pathological hallmark of PD, and of α-synuclein (SNCA) point mutations and multiplications as rare causes of PD.24 Disease severity correlates with the number of SNCA alleles in multiplication carriers. Patients with SNCA triplication present with an early-onset aggressive form of PD with dementia, psychiatric features, and dysautonomia.5 On the other hand, SNCA duplications are not fully penetrant and are associated with variable clinical features ranging from late-onset sporadic PD to presentations indistinguishable from those in triplication carriers, although the reasons underlying this variability are unknown.

Herein, we report a new kindred carrying the largest nonchromosomal duplication of the SNCA locus identified to date, to our knowledge, presenting with clinical features reminiscent of frontotemporal dementia (FTD) and widespread LBs. We undertook a comprehensive assessment of candidate disease modifiers in carriers of SNCA locus duplications based on genetic analysis of the proband and statistical analysis of previously published cases.

Methods
Genetics

Participants provided written, oral, or next of kin informed consent and the study was ethically approved by University College London (UCL). Microtubule-associated protein tau (MAPT) was screened through Sanger sequencing in patients III:1 and III:3 (Figure 1A) because of clinical similarity to FTD.6 Owing to clinical similarities to SNCA multiplication patients and widespread α-synuclein protein pathology, a genomic DNA sample from patient III:1 was assessed for whole-gene SNCA multiplications with the multiplex ligation–dependent probe amplification kit P051C (Microbiology Research Centre, Holland).7 The approximate break points of the duplication were determined through a custom 8×60k dense comparative genomic hybridization array (Agilent) designed as part of a larger ongoing study with dense spacing of probes throughout the SNCA genomic region (details available from C.P. by request).

To identify genetic risk factors potentially influencing the clinical features, a DNA sample from patient III:1 was genotyped on ImmunoChip, an Illumina array of custom content with a specific focus on immune-related and PD/parkinsonism genes.810 We focused on risk variants identified through previously published PD genome-wide association studies and on mutations and risk factors located within PD genes (see Supplementary Information for methods, http://www.ucl.ac.uk/ukpdc/publications/data/Kara_et_al_2014_supplement_Jama_Neurology.pdf).

Neuropathology

The brain of patient III:3 was fixed by suspension in buffered 20% formalin and sampled extensively for neuropathology. Paraffin-embedded sections (8 μm) from cortical, subcortical, brainstem, and cerebellar regions were stained immunohistochemically for standard pathological markers including β-amyloid (DAKO, M0872), AT8 (Tau Ser202/Thr205, Source Bioscience 90206), transactive response DNA-binding protein 43 (TDP-43; Abnova, H00023435-M01), and α-synuclein (Abcam, ab15530). For β-amyloid and α-synuclein immunohistochemistry, sections required pretreatment with formic acid for 10 minutes prior to antigen retrieval. Antigen retrieval was achieved by heating sections in a pressure cooker for 10 minutes in boiling citrate buffer (pH, 6.0). Endogenous peroxidase activity was blocked with methanol/0.3% H2O2, followed by incubation in dried milk solution (10% in phosphate-buffered saline, 30 minutes) to block nonspecific antibody binding. Primary antibodies diluted in phosphate-buffered saline were applied for 60 minutes at room temperature and staining was visualized by the streptavidin-biotin-peroxidase method (Vector Laboratories) using 3.3’-diaminobenzidine as the chromogen with Mayer hematoxylin counterstaining.

Statistical Analysis of Previously Published Cases

We reviewed previously published articles on carriers of SNCA locus duplications to assess whether the length of the duplication influences penetrance and disease severity and whether longer duplication sizes are related to a younger age at onset, indicating a contribution of increased dosage of other gene(s) to the development of disease. We used a duplication size threshold of 5 Mb as an inclusion criterion, which was chosen on the basis of the following arguments: (1) we hypothesized that shorter duplications are more frequently nonpenetrant and as duplication size increases, the individual exhibits a more severe phenotype ranging from sporadic PD to PD dementia to indistinguishable from triplication carriers and (2) we hypothesized that above a certain duplication length threshold, the individual would exhibit a more complex phenotype with features unusual for SNCA multiplications. Consequently, 2 individuals with such complex presentations, 1 described by Garraux et al11 and the patient reported herein, carrying duplications larger than 5 Mb were excluded from this analysis. Published individuals were also excluded if any of the following were true: (1) there was no information on the length of the duplication, (2) there was insufficient clinical information, (3) clinical presentation was clearly inconsistent with parkinsonism, or (4) they were affected relatives of probands with SNCA duplications but their carrier status was not assessed (Supplementary Figure 1, http://www.ucl.ac.uk/ukpdc/publications/data/Kara_et_al_2014_supplement_Jama_Neurology.pdf). Data on all eligible individuals from each family carrying the duplications were included in the study to maximize study power (Supplementary Table 1, http://www.ucl.ac.uk/ukpdc/publications/data/Kara_et_al_2014_supplement_Jama_Neurology.pdf). Review of the articles’ eligibility and cataloging of the information was undertaken twice.

Disease severity was measured by deriving a composite score for each affected individual from the published data. Each individual was assigned a score according to a clinical presentation point system as follows: typical PD/parkinsonism = 1, young onset (≤40 years) = 1, dementia = 1, hallucinations = 1, dysautonomia = 1, depression = 1, and any additional features (eg, dystonia, epilepsy, sleep disturbances, myoclonus, or psychiatric features) = 1. These scores were then summed to form a composite score, which ranged from 0 (unaffected) to 6 (severely affected).

Numerical data were summarized using mean and standard deviation or median and range depending on data distribution. Categorical data were summarized using counts and percentages. We used Spearman rank correlation to quantify the strength of the monotonic association between duplication size and each of age at onset and disease severity. The main outcomes of interest were disease status (binary), disease severity (ordinal), and age at onset (binary). We modeled binary outcomes using logistic regression with robust sandwich estimation of the variance to account for the clustering effect at the family level.12 We modeled ordinal outcomes using ordinal regression with the proportional odds assumption adjusted for clusters at the family level.13 This approach has been shown to be more suitable than multilevel approaches in the presence of a small number of clusters with a low number of individuals.14 We investigated the individual effect of the covariates on each of the outcomes using univariable analyses. We also investigated their combined effect using multivariable analyses.

The functional form of the relationship between duplication size and each outcome was also graphically evaluated. Model fit was assessed using the Akaike Information Criterion15 (AIC), where smaller AIC is preferred.

All statistical analyses were completed using Stata16 and plots were generated with the statistical package R version 3.0.217 using the package ggplot2.18 Results from modeling are presented as estimates (95% CI).18

Results
Case Report
Clinical Description

The proband, a woman from the United Kingdom who is white (patient III:3, Figure 1A), first developed lifelong and progressive symptoms of extreme anxiety, panic disorder, and hallucinations from age 8 years that were managed adequately with medication up to her mid-20s when she had to quit her job. At age 38 years, she developed a right arm tremor followed by a progressive akinetic-rigid syndrome plus a classic pill-rolling tremor, complicated by worsening obsessive behavior, walking disturbances and falls, increased salivation, rapid eye movement sleep behavior disorder, personality changes, short-term memory impairment, and poor self-care. She also had facial, head, and tongue tremors accompanied by blepharospasm, a dystonic neck, and dysarthria. Levodopa/benserazide hydrochloride treatment improved her walking but increased her falls. Neuropsychometry testing showed frontal and temporal deficits, although neuroimaging findings were normal. There was a history of recurrent unexplained blackouts or seizures. Electroencephalography showed traces of alpha-rhythm and autonomic testing indicated cardiovascular autonomic failure. On examination, she exhibited akinesia and rigidity of all 4 limbs, rest tremor, and hypometric saccades. From 42 years of age, the motor and cognitive aspects of her disorder declined further, with poor concentration, frontal release signs, wandering, repetitive speech, and a profound increase in appetite particularly for sweet foods. At age 46 years, she was given a clinical diagnosis of possible FTD with parkinsonism-17 but no MAPT mutations were detected. She became bedbound and died at the age of 49 years.

Her father (patient II:3), paternal grandmother (patient I:1), and 2 paternal great-aunts (patients I:2 and I:3) had PD with no documented dementia. Her paternal cousin (patient III:1) was diagnosed as having possible FTD parkinsonism-17 in his early 50s when he presented with memory problems, hallucinations, and falls, complicated by alcoholism. This progressed with increasing cognitive decline, disorientation, and rigidity, at which point his progressive condition was managed by local services.

Pathology

Neuropathological examination showed neuronal loss, which was most severe in the substantia nigra, moderate in the locus coeruleus and dorsal motor nucleus of the vagus, and mild in the nucleus basalis of Meynert and cerebellar Purkinje cells. Neuronal loss was not observed in other regions including the hippocampus. Widespread LBs and Lewy neurites affecting brainstem, limbic, and neocortical regions corresponding to neocortical LB pathology, Braak stage 6 (Figure 1B, a-d),19,20 were detected. The hippocampus showed mild accumulation of α-synuclein inclusions with severe neuritic pathology in the cornu ammonis 2 region (Figure 1B, e and f). Occasional oligodendrocytes contained α-synuclein immunoreactive inclusions resembling coiled bodies (Figure 1B, g and h). No inclusions resembling glial cytoplasmic inclusions were observed. Minimal phospho-tau pathology was present in the transentorhinal cortex corresponding to Braak and Braak stage 1 (Figure 1B, i and j) and there were sparse diffuse cortical β-amyloid deposits; transactive response DNA-binding protein 43 pathology was not present.

Genetics

Test results for case III:1 were negative for MAPT point mutations but the patient was found to carry a heterozygous SNCA duplication on multiplex ligation–dependent probe amplification (Figure 2A). Comparative genomic hybridization arrays showed that the duplication extended over approximately 6.4 Mb (chr4:88349207-94751141, corresponding to the first and the last duplicated probes, respectively; human build 37) and contained 37 genes including SNCA (Figure 2B and C) (Table 1). The first and last nonduplicated probes were A_14_P119434 (chr4:88295927-88295986) and A_14_P124103 (chr4:94859877-94859936) (Figure 2D). The break points were located centromeric to intron 1 of the NUDT9 gene (NM_198038.2) and telomeric to the ATOH1 gene (Figure 2E).

The patient was homozygous for the wild-type allele for all rare single-nucleotide polymorphisms or probes encoding mutations on ImmunoChip, apart from 1 heterozygous parkin variant that is probably nonpathogenic (rs1801334; minor allele frequency 0.04 in European populations as catalogued in ensembl) (Supplementary Table 2, http://www.ucl.ac.uk/ukpdc/publications/data/Kara_et_al_2014_supplement_Jama_Neurology.pdf) and had a MAPT haplotype of H1/H1. The patient carried a total of 18/46 risk alleles for 23 genome-wide association study single-nucleotide polymorphisms (Supplementary Table 3, http://www.ucl.ac.uk/ukpdc/publications/data/Kara_et_al_2014_supplement_Jama_Neurology.pdf), placing him in the third risk quintile shown to confer approximately a 77% increase in PD risk.22,29,30

Statistical Analysis

Table 2 describes the demographic and clinical characteristics of individuals included in the statistical analysis. Overall, 73% (27/37) of individuals were affected, with a higher proportion of women compared with men in the unaffected group (90% vs 10%). The median age at onset of disease was 47 years (range, 31-71 years). The median composite score was 2 (range, 0-6). The median duplication size for affected and unaffected individuals was 0.63 Mb (range, 0.2-5) and 0.6 Mb (range, 0.4-3.47 Mb), respectively. There was a weak positive monotonic association between duplication size and composite score (ρ = 0.17, P = .31) and between duplication size and age at onset (ρ = 0.12, P = .56).

Table 3 provides estimates of the effect of duplication size and sex on disease status, age at onset, and disease severity. Overall, only the effect of sex on disease status and disease severity reached statistical significance for both univariable and multivariable models (P < .05). The odds of being affected were more than 8-fold for men compared with women. The corresponding odds ratio (OR) was 8.36 (95% CI, 1.97-35.42). The odds of being affected increased by approximately 34% for each unit increase in duplication size. The corresponding OR was 1.34 (95% CI, 0.78-2.31). Men had a 77% greater chance of developing an early-onset form of disease in comparison with women, with an OR of 0.23 (95% CI, 0.04-1.28), whereas an increase in duplication size by 1 unit resulted in a 6% decrease in the chance of developing late-onset disease (OR, 0.94; 95% CI, 0.71-1.24). Men had more than a 5-fold increase in the chance of developing a more severe disease and disease severity increased by 17% for each unit increase in duplication size. The corresponding ORs were 5.55 (95% CI, 1.39-22.22) and 1.17 (95% CI, 0.81-1.68), respectively. (All ORs quoted refer to univariable models.)

Discussion

A total of 29 kindreds carrying SNCA locus duplications have been reported in the literature,31 with pathology information on 4 duplication patients (3 belonging to the same family)3236 (Supplementary Table 4, http://www.ucl.ac.uk/ukpdc/publications/data/Kara_et_al_2014_supplement_Jama_Neurology.pdf). The size of the duplicated region has been studied in 17 kindreds/sporadic cases (Supplementary Table 4) and has been found to vary greatly, from 0.2 Mb37 to 41.2 Mb,11 containing from 2 to 150 genes (Figure 2E and F; Supplementary Table 5, http://www.ucl.ac.uk/ukpdc/publications/data/Kara_et_al_2014_supplement_Jama_Neurology.pdf). To our knowledge, the case described herein carries the largest submicroscopic duplication of the SNCA locus reported to date.

Although we were not able to determine the exact break points of the duplication, in accordance with Ibáñez et al,38 we showed that these lie within regions rich in repetitive elements and especially transposable elements (long interspersed elements, short interspersed elements, and long–terminal repeat retrotransposons), facilitating the insertion of additional copies of flanking sequences in the genome,39 allowing nonhomologous recombination events leading to genomic structural rearrangements. The 4q22 region is known to be inherently prone to disruption as a fragile site (FRA4F), which was originally described as a 7 Mb region corresponding very closely to the duplicated region in this report.40 Subsequent work has extended the fragile site from 88 200 000 to 99 100 000 Mb41 but the centromeric boundary still corresponds to the centromeric break point in our report. Other reported copy number variants are mostly within the confines of the fragile site, although a break point centromeric to the proposed FRA4F boundary has been documented in some cases (Figure 2F and G).

This study further emphasizes the clinical variability and expands the phenotypic spectrum associated with SNCA duplications, representing the first case with such a complex presentation and substantial overlap with other dementing and psychiatric disorders. Duplications of the SNCA gene are characterized by incomplete penetrance and variable clinical presentations,34,42 occasionally being indistinguishable from sporadic PD38 or having the core clinical features of young-onset PD dementia with dysautonomia, depression, and hallucinations, resembling the phenotype of SNCA triplications.5 Our patient exhibited some of the main features associated with SNCA multiplications (young-onset PD dementia, hallucinations, rapid-eye movement sleep-behavior disorder, and dysautonomia), which are, however, part of a more complicated phenotype reminiscent of FTD. To our knowledge, obsessive-compulsive disorder and anxiety have not been previously reported in any patient with an SNCA duplication, nor were they present in any other member of the family we analyzed. Although it is possible these were causally related in our patient III:3, it is more likely a coincidental occurrence. However, this does make it difficult to establish with certainty the exact age at onset of the patient (possibly age 8 years or age 38 years). Intrafamilial variability was marked as 2 members had an FTD-like phenotype and 4 family members from older generations apparently had typical PD. Patient II:1, an obligate carrier, was an alcoholic as was his son (patient III:1) and died at age 70 years without documented parkinsonism or dementia.

Neuropathological examination findings showed features corresponding to idiopathic PD and SNCA duplication cases, with widespread Lewy pathology extending into neocortical regions (Braak and Braak stage 6) and no transactive response DNA-binding protein 43 pathology.32,3436 There was only minimal Alzheimer pathology with tau pathology, limited to Braak and Braak stage 1 and sparse diffuse β-amyloid deposition in the cortex. Although previous studies have suggested cross-seeding between α-synuclein and tau,43 the relatively low accumulation of tau compared with α-synuclein–containing inclusions suggested that this tau accumulation was a normal consequence of aging. Unlike other reported cases of SNCA duplication, neuronal loss was restricted and did not affect the hippocampus.32,35 In further contrast, oligodendroglial inclusions resembling coiled bodies were observed but there were no structures resembling glial cytoplasmic inclusions.32 However, as has been reported, hippocampal pathology, particularly neuritic α-synuclein deposition, was severe especially in the cornu ammonis 2 region.

Given that SNCA duplications are frequently nonpenetrant,31,34 it is possible that mutations in another gene are responsible for the unusual clinical presentation of the proband. However, there are several lines of evidence supporting the pathogenicity of the duplication. The widespread LB pathology and other pathological features are consistent with SNCA duplications, the pattern of inheritance of the disease in the family is autosomal dominant with possible reduced penetrance, and other affected relatives have phenotypes that have been previously associated with SNCA duplication. Thus, although we were unable to confirm complete segregation owing to the lack of DNA samples, the SNCA duplication is most likely to be responsible for the disease in this family.

The reasons underlying this clinical variability associated with SNCA duplication are currently unknown, although several preliminary hypotheses emerged from our analyses that require validation in future studies on larger cohorts of SNCA duplication carriers. We found trends for association between duplication size and disease status, age at onset, and disease severity that did not reach statistical significance, although association with sex did. Although our study was underpowered to detect association (n = 37),44,45 it is possible that larger duplication size may not independently produce disease without the contribution of additional risk factors. Sex-specific risk factors are an intriguing possibility as regression-model fitting was improved after adjusting for sex (Table 3), and men with SNCA duplications had an 8-fold increase in risk for developing PD. A predilection for male involvement is well known for sporadic PD.46,47 Alternatively, an increased burden of other risk factors could have a disease-modifying role; the patient we report herein carried 1 single heterozygous parkin rare variant had an H1/H1 MAPT haplotype and an accumulation of risk alleles in loci identified through genome-wide association studies. Similarly, Itokawa et al42 reported a patient with an SNCA duplication carrying a PD risk factor (p.G2385R) within LRRK2. Other unexplored possibilities include increased dosage of common or rare variants with a regulatory effect on expression or other properties of α-synuclein,48,49 mosaicism,50 environmental factors,51 or stochasticity.52

Conclusions

Patients in whom complex presentations of onset in early adulthood with dementia and parkinsonism, complicated by multiple cognitive, psychiatric, and motor features, should be considered for genetic testing for SNCA multiplication. Understanding the genetic modifiers influencing the phenotype of SNCA duplications may be important in elucidating the mechanisms underlying α-synuclein accumulation and the formation of LBs.

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Article Information

Corresponding Author: Henry Houlden, MD, PhD, Department of Molecular Neuroscience, UCL Institute of Neurology, Queen Square, WC1N 3BG, London, United Kingdom (h.houlden@ucl.ac.uk).

Accepted for Publication: April 4, 2014.

Published Online: July 7, 2014. doi:10.1001/jamaneurol.2014.994.

Author Contributions: Drs Kara and Houlden had full access to all of the data in the study and take responsibility for the integrity of the data and the accuracy of the data analysis.

Study concept and design: Kara, Rantell, Singleton, Hardy, Holton, Houlden.

Acquisition, analysis, or interpretation of data: Kara, Kiely, Proukakis, Giffin, Love, Hehir, Rantell, Pandraud, Hernandez, Nacheva, Pittman, Nalls, Singleton, Revesz, Bhatia, Quinn, Hardy, Holton.

Drafting of the manuscript: Kara, Kiely, Holton, Houlden.

Critical revision of the manuscript for important intellectual content: All authors.

Statistical analysis: Kara, Rantell.

Obtained funding: Proukakis, Singleton, Revesz, Hardy, Holton, Houlden.

Administrative, technical, or material support: Hehir, Rantell, Pandraud, Hernandez, Nacheva, Pittman, Nalls, Singleton.

Study supervision: Proukakis, Love, Rantell, Hernandez, Pittman, Nalls, Singleton, Revesz, Bhatia, Quinn, Hardy, Holton, Houlden.

Conflict of Interest Disclosures: Dr Bhatia received funding for travel from GlaxoSmithKline, Orion Corp, Ipsen, and Merz Pharmaceuticals LLC; serves on the editorial boards of Movement Disorders and Therapeutic Advances in Neurological Disorders; receives royalties from the publication of Oxford Specialist Handbook of Parkinson’s Disease and Other Movement Disorders (Oxford University Press, 2008); received speaker honoraria from GlaxoSmithKline, Ipsen, Merz Pharmaceuticals LLC, and Sun Pharmaceutical Industries Ltd; received personal compensation for participation on the scientific advisory board for GlaxoSmithKline and Boehringer Ingelheim; and received research support from Ipsen and from the Halley Stewart Trust through Dystonia Society United Kingdom. No other disclosures were reported.

Funding/Support: This study was supported by the Parkinson’s Disease Foundation and grant WT089698 from the Wellcome Trust/Medical Research Council Joint Call in Neurodegeneration received by the United Kingdom Parkinson’s Disease Consortium whose members are from the UCL Institute of Neurology, the University of Sheffeld, and the Medical Research Council Protein Phosphorylation Unit at the University of Dundee. Dr Holton is supported by the Reta Lila Weston Institute for Neurological Studies, the Multiple System Atrophy Trust, Alzheimer’s Research United Kingdom, and Parkinson’s United Kingdom. Dr Kiely is supported by the Multiple System Atrophy Trust. Dr Bhatia received grant G-1009 from Parkinson’s United Kingdom and a grant from the Dystonia Coalition. This study was supported in part by the Intramural Research Program of the National Institute on Aging, National Institutes of Health, project ZO1 AG000949-08 from the Department of Health and Human Services and the National Institute for Health Research, UCL Hospitals Biomedical Research Centre.

Role of the Sponsor: The funders had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; preparation, review, or approval of the manuscript; and decision to submit the manuscript for publication.

Additional Contributions: We thank the patients and their families for their help and sample donations and the Queen Square Brain Bank and the South West Dementia Brain Bank for their provision of human tissue.

References
1.
Spillantini  MG, Schmidt  ML, Lee  VM, Trojanowski  JQ, Jakes  R, Goedert  M.  Alpha-synuclein in Lewy bodies. Nature. 1997;388(6645):839-840.
PubMedArticle
2.
Polymeropoulos  MH, Lavedan  C, Leroy  E,  et al.  Mutation in the alpha-synuclein gene identified in families with Parkinson’s disease. Science. 1997;276(5321):2045-2047.
PubMedArticle
3.
Singleton  AB, Farrer  M, Johnson  J,  et al.  alpha-Synuclein locus triplication causes Parkinson’s disease. Science. 2003;302(5646):841.
PubMedArticle
4.
Ibáñez  P, Bonnet  AM, Débarges  B,  et al.  Causal relation between alpha-synuclein gene duplication and familial Parkinson’s disease. Lancet. 2004;364(9440):1169-1171.
PubMedArticle
5.
Gwinn  K, Devine  MJ, Jin  LW,  et al.  Clinical features, with video documentation, of the original familial lewy body parkinsonism caused by α-synuclein triplication (Iowa kindred). Mov Disord. 2011;26(11):2134-2136.
PubMedArticle
6.
Kara  E, Ling  H, Pittman  AM,  et al.  The MAPT p.A152T variant is a risk factor associated with tauopathies with atypical clinical and neuropathological features. Neurobiol Aging. 2012;33(9):e7, e14.
PubMedArticle
7.
Schouten  JP, McElgunn  CJ, Waaijer  R, Zwijnenburg  D, Diepvens  F, Pals  G.  Relative quantification of 40 nucleic acid sequences by multiplex ligation-dependent probe amplification. Nucleic Acids Res. 2002;30(12):e57.
PubMedArticle
8.
Plagnol  V, Nalls  MA, Bras  JM,  et al; International Parkinson’s Disease Genomics Consortium (IPDGC); Wellcome Trust Case Control Consortium 2 (WTCCC2).  A two-stage meta-analysis identifies several new loci for Parkinson’s disease. PLoS Genet. 2011;7(6):e1002142.
PubMedArticle
9.
Jostins  L, Ripke  S, Weersma  RK,  et al; International IBD Genetics Consortium (IIBDGC).  Host-microbe interactions have shaped the genetic architecture of inflammatory bowel disease. Nature. 2012;491(7422):119-124.
PubMedArticle
10.
Faraco  J, Lin  L, Kornum  BR,  et al.  ImmunoChip study implicates antigen presentation to T cells in narcolepsy. PLoS Genet. 2013;9(2):e1003270.
PubMedArticle
11.
Garraux  G, Caberg  JH, Vanbellinghen  JF,  et al.  Partial trisomy 4q associated with young-onset dopa-responsive parkinsonism. Arch Neurol. 2012;69(3):398-400.
PubMedArticle
12.
Williams  RL.  A note on robust variance estimation for cluster-correlated data. Biometrics. 2000;56(2):645-646.
PubMedArticle
13.
Harrell  FE  Jr, Margolis  PA, Gove  S,  et al; WHO/ARI Young Infant Multicentre Study Group.  Development of a clinical prediction model for an ordinal outcome: the World Health Organization Multicentre Study of Clinical Signs and Etiological agents of Pneumonia, Sepsis and Meningitis in Young Infants. Stat Med. 1998;17(8):909-944.
PubMedArticle
14.
Austin  PC.  Estimating multilevel logistic regression models when the number of clusters is low: a comparison of different statistical software procedures. Int J Biostat. 2010;6(1):16.
PubMed
15.
Chirwa  ED, Griffiths  PL, Maleta  K, Norris  SA, Cameron  N.  Multi-level modelling of longitudinal child growth data from the Birth-to-Twenty Cohort: a comparison of growth models. Ann Hum Biol. 2014;41(2):166-177.
PubMedArticle
16.
StataCorp. Stata Statistical Software: Release 12. College Station, TX: StataCorp LP; 2011.
17.
Team RCR. A language and environment for statistical computing. R Foundation for Statistical Computing, Vienna, Austria. http://www.r-project.org/. 2013. Accessed June 2014.
18.
Wickham  H. ggplot2: Elegant Graphics for Data Analysis. New York, NY: Springer; 2009.
19.
Braak  H, Alafuzoff  I, Arzberger  T, Kretzschmar  H, Del Tredici  K.  Staging of Alzheimer disease-associated neurofibrillary pathology using paraffin sections and immunocytochemistry. Acta Neuropathol. 2006;112(4):389-404.
PubMedArticle
20.
McKeith  IG, Dickson  DW, Lowe  J,  et al; Consortium on DLB.  Diagnosis and management of dementia with Lewy bodies: third report of the DLB Consortium. Neurology. 2005;65(12):1863-1872.
PubMedArticle
21.
Simon-Sanchez  J, Scholz  S, Fung  HC,  et al.  Genome-wide SNP assay reveals structural genomic variation, extended homozygosity and cell-line induced alterations in normal individuals. Hum Mol Genet. 2007;16(1):1-14.
PubMedArticle
22.
Nalls  MA, Plagnol  V, Hernandez  DG,  et al; International Parkinson Disease Genomics Consortium.  Imputation of sequence variants for identification of genetic risks for Parkinson’s disease: a meta-analysis of genome-wide association studies. Lancet. 2011;377(9766):641-649.
PubMedArticle
23.
Simón-Sánchez  J, Schulte  C, Bras  JM,  et al.  Genome-wide association study reveals genetic risk underlying Parkinson’s disease. Nat Genet. 2009;41(12):1308-1312.
PubMedArticle
24.
Zhang  X, Zhao  J, Li  C,  et al.  DSPP mutation in dentinogenesis imperfecta Shields type II. Nat Genet. 2001;27(2):151-152.
PubMedArticle
25.
Xiao  S, Yu  C, Chou  X,  et al.  Dentinogenesis imperfecta 1 with or without progressive hearing loss is associated with distinct mutations in DSPP. Nat Genet. 2001;27(2):201-204.
PubMedArticle
26.
Lorenz-Depiereux  B, Bastepe  M, Benet-Pagès  A,  et al.  DMP1 mutations in autosomal recessive hypophosphatemia implicate a bone matrix protein in the regulation of phosphate homeostasis. Nat Genet. 2006;38(11):1248-1250.
PubMedArticle
27.
Mochizuki  T, Wu  G, Hayashi  T,  et al.  PKD2, a gene for polycystic kidney disease that encodes an integral membrane protein. Science. 1996;272(5266):1339-1342.
PubMedArticle
28.
Hills  LB, Masri  A, Konno  K,  et al.  Deletions in GRID2 lead to a recessive syndrome of cerebellar ataxia and tonic upgaze in humans. Neurology. 2013;81(16):1378-1386.
PubMedArticle
29.
Hernandez  DG, Nalls  MA, Ylikotila  P,  et al.  Genome wide assessment of young onset Parkinson’s disease from Finland. PLoS One. 2012;7(7):e41859.
PubMedArticle
30.
Kara  E, Xiromerisiou  G, Spanaki  C,  et al.  Assessment of Parkinson’s disease risk loci in Greece. Neurobiol Aging. 2014;35(2):e9-e16, e16.
PubMedArticle
31.
Elia  AE, Petrucci  S, Fasano  A,  et al.  Alpha-synuclein gene duplication: marked intrafamilial variability in two novel pedigrees. Mov Disord. 2013;28(6):813-817.
PubMedArticle
32.
Ikeuchi  T, Kakita  A, Shiga  A,  et al.  Patients homozygous and heterozygous for SNCA duplication in a family with parkinsonism and dementia. Arch Neurol. 2008;65(4):514-519.
PubMedArticle
33.
Wakabayashi  K, Hayashi  S, Ishikawa  A,  et al.  Autosomal dominant diffuse Lewy body disease. Acta Neuropathol. 1998;96(2):207-210.
PubMedArticle
34.
Nishioka  K, Hayashi  S, Farrer  MJ,  et al.  Clinical heterogeneity of alpha-synuclein gene duplication in Parkinson’s disease. Ann Neurol. 2006;59(2):298-309.
PubMedArticle
35.
Obi  T, Nishioka  K, Ross  OA,  et al.  Clinicopathologic study of a SNCA gene duplication patient with Parkinson disease and dementia. Neurology. 2008;70(3):238-241.
PubMedArticle
36.
Ross  OA, Braithwaite  AT, Skipper  LM,  et al.  Genomic investigation of alpha-synuclein multiplication and parkinsonism. Ann Neurol. 2008;63(6):743-750.
PubMedArticle
37.
Nishioka  K, Ross  OA, Ishii  K,  et al.  Expanding the clinical phenotype of SNCA duplication carriers. Mov Disord. 2009;24(12):1811-1819.
PubMedArticle
38.
Ibáñez  P, Lesage  S, Janin  S,  et al; French Parkinson’s Disease Genetics Study Group.  Alpha-synuclein gene rearrangements in dominantly inherited parkinsonism: frequency, phenotype, and mechanisms. Arch Neurol. 2009;66(1):102-108.
PubMedArticle
39.
Ivics  Z, Izsvák  Z.  Repetitive elements and genome instability. Semin Cancer Biol. 2010;20(4):197-199.
PubMedArticle
40.
Rozier  L, El-Achkar  E, Apiou  F, Debatisse  M.  Characterization of a conserved aphidicolin-sensitive common fragile site at human 4q22 and mouse 6C1: possible association with an inherited disease and cancer. Oncogene. 2004;23(41):6872-6880.
PubMedArticle
41.
Fungtammasan  A, Walsh  E, Chiaromonte  F, Eckert  KA, Makova  KD.  A genome-wide analysis of common fragile sites: what features determine chromosomal instability in the human genome? Genome Res. 2012;22(6):993-1005.
PubMedArticle
42.
Itokawa  K, Sekine  T, Funayama  M,  et al.  A case of α-synuclein gene duplication presenting with head-shaking movements. Mov Disord. 2013;28(3):384-387.
PubMedArticle
43.
Guo  JL, Covell  DJ, Daniels  JP,  et al.  Distinct α-synuclein strains differentially promote tau inclusions in neurons. Cell. 2013;154(1):103-117.
PubMedArticle
44.
Bonett  DG, Right  TAW.  Sample size requirements for estimating pearson, kendall, and spearman correlations. Psychometrika.2000;65(1):23-28. doi: 10.1007/BF02294183Article
45.
Hsieh  FY.  Sample size tables for logistic regression. Stat Med. 1989;8(7):795-802.
PubMedArticle
46.
Wooten  GF, Currie  LJ, Bovbjerg  VE, Lee  JK, Patrie  J.  Are men at greater risk for Parkinson’s disease than women? J Neurol Neurosurg Psychiatry. 2004;75(4):637-639.
PubMedArticle
47.
Taylor  KS, Cook  JA, Counsell  CE.  Heterogeneity in male to female risk for Parkinson’s disease. J Neurol Neurosurg Psychiatry. 2007;78(8):905-906.
PubMedArticle
48.
Spencer  CC, Plagnol  V, Strange  A,  et al; UK Parkinson’s Disease Consortium; Wellcome Trust Case Control Consortium 2.  Dissection of the genetics of Parkinson’s disease identifies an additional association 5′ of SNCA and multiple associated haplotypes at 17q21. Hum Mol Genet. 2011;20(2):345-353.
PubMedArticle
49.
Rhinn  H, Qiang  L, Yamashita  T,  et al.  Alternative α-synuclein transcript usage as a convergent mechanism in Parkinson’s disease pathology. Nat Commun. 2012;3:1084.
PubMedArticle
50.
Proukakis  C, Houlden  H, Schapira  AH.  Somatic alpha-synuclein mutations in Parkinson’s disease: hypothesis and preliminary data. Mov Disord. 2013;28(6):705-712.
PubMedArticle
51.
Baranzini  SE, Mudge  J, van Velkinburgh  JC,  et al.  Genome, epigenome and RNA sequences of monozygotic twins discordant for multiple sclerosis. Nature. 2010;464(7293):1351-1356.
PubMedArticle
52.
Xiromerisiou  G, Houlden  H, Sailer  A, Silveira-Moriyama  L, Hardy  J, Lees  AJ.  Identical twins with Leucine rich repeat kinase type 2 mutations discordant for Parkinson’s disease. Mov Disord. 2012;27(10):1323.
PubMedArticle
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