REVIEW

Genotype-Phenotype Relations for the Parkinson’s Disease , PINK1, DJ1: MDSGene Systematic Review

Meike Kasten, MD,1,2 Corinna Hartmann, MD,1 Jennie Hampf, MD,1 Susen Schaake, BSc,1 Ana Westenberger, PhD,1 Eva-Juliane Vollstedt, MD,1 Alexander Balck, MD,1 Aloysius Domingo, MD, PhD,1 Franca Vulinovic, PhD,1 Marija Dulovic, MD, PhD,1 Ingo Zorn,3 Harutyun Madoev,1 Hanna Zehnle,1 Christina M. Lembeck, BSc,1 Leopold Schawe, BSc,1 Jennifer Reginold, BSc,4 Jana Huang, BHS,4 Inke R. Konig,€ PhD,5 Lars Bertram, MD,3,6 Connie Marras, MD, PhD,4 Katja Lohmann, PhD,1 Christina M. Lill, MD, MSc,1 and Christine Klein, MD1*

1Institute of Neurogenetics, University of Lubeck,€ Lubeck,€ Germany 2Department of Psychiatry and Psychotherapy, University of Lubeck,€ Lubeck,€ Germany 3Lubeck€ Interdisciplinary Platform for Genome Analytics (LIGA), Institutes of Neurogenetics & Integrative and Experimental Genomics, University of Lubeck,€ Lubeck,€ Germany 4The Morton and Gloria Shulman Movement Disorders Centre and the Edmond J Safra Program in Parkinson’s Disease, Toronto Western Hospital, University of Toronto, Toronto, Ontario, Canada 5Institute of Medical Biometry and Statistics, University of Lubeck,€ Lubeck,€ Germany 6School of Public Health, Faculty of Medicine, Imperial College London, London, UK

ABSTRACT: This first comprehensive MDSGene early onset (median age at onset of ~30 years for car- review is devoted to the 3 autosomal recessive Parkin- riers of at least 2 mutations in any of the 3 genes) of an son’s disease forms: PARK-Parkin, PARK-PINK1, and overall clinically typical form of PD with excellent treat- PARK-DJ1. It followed MDSGene’s standardized data ment response, dystonia and dyskinesia being relatively extraction protocol and screened a total of 3652 cita- common and cognitive decline relatively uncommon. tions and is based on fully curated phenotypic and However, when comparing actual data with common genotypic data on >1100 patients with recessively expert knowledge in previously published reviews, we inherited PD because of 221 different disease-causing detected several discrepancies. We conclude that sys- mutations in Parkin, PINK1,orDJ1. All these data are tematic reporting of phenotypes is a pressing need in also available in an easily searchable online database light of increasingly available molecular genetic testing (www.mdsgene.org), which also provides descriptive and the emergence of first -specific therapies summary statistics on phenotypic and genetic data. entering clinical trials. VC 2018 International Parkinson Despite the high degree of missingness of phenotypic and Movement Disorder Society features and unsystematic reporting of genotype data in the original literature, the present review recapitulates Key Words: Parkin; PRKN; PARK2; PINK1; PARK7; many of the previously described findings including DJ1; Parkinson’s disease; genetics

------*Correspondence to: Christine Klein, MD, Institute of Neurogenetics, University of Lubeck,€ Maria-Goeppert-Str. 1, 23562 Lubeck,€ Germany; The increasing cost-efficiency of genetic testing and [email protected] recent technological advances including next- Meike Kasten, Corinna Hartmann, Jennie Hampf, Susen Schaake, generation sequencing techniques have led to a sub- Christina M. Lill, and Christine Klein contributed equally to this work. stantial increase in the number of publications and Relevant conflicts of interest/financial disclosures: There is no finan- cial conflict of interest. the spectrum of reported mutations potentially causa- Funding agencies: The study was supported by the Movement Disorder tive for human diseases. This growing body of data is Society (to C.K., C.M., C.M.L., and L.B.), by the Deutsche Forschungs- becoming increasingly difficult to follow and inter- gemeinschaft (FOR2488; to C.K., M.K., A.W., K.L., L.B., I.R.K., and pret. The vast majority of reviews on inherited dis- C.M.L.), by the Possehl Foundation (to C.M.L.), and by intramural funds from the University of Luebeck (to C.K.). eases including movement disorders are narrative, Received: 20 October 2017; Revised: 12 January 2018; Accepted: 16 that is, they provide a qualitative and thereby subjec- January 2018 tive and selective account of the available literature. To date, very few systematic review articles are avail- Published online 11 April 2018 in Wiley Online Library 1 2 (wileyonlinelibrary.com). DOI: 10.1002/mds.27352 able (eg, see references and )thatprovideacase-

730 Movement Disorders, Vol. 33, No. 5, 2018 MDSGene REVIEW: Parkin, PINK1, DJ1 by-case unbiased account of the entire published Titles, abstracts, and, where applicable, full texts of English-language literature by quantifying all avail- peer-reviewed original articles in English and pub- able data. lished until September 20, 2017, were screened for Causative mutations in the autosomal-recessive Par- inclusion in the systematic review. Only articles kinson’s disease (PD) genes PRKN (commonly and reporting at least 1 patient likely harboring biallelic therefore also in this article referred to as Parkin), Parkin, PINK1,orDJ1 mutations were selected. In PINK1, and PARK7 (commonly and therefore also in addition, reviews on any of the 3 disease genes of this article referred to as DJ1) account for approxi- interest were screened for additional data and further, mately 13% of early-onset PD, that is, PD occurring potentially eligible articles. For an overview of the lit- 3 before the age of 40 years. In this study, we present erature search as well as the filtering procedure, see the first systematic MDSGene review and devote it to Supplementary Figure 1A. A list of all eligible articles autosomal-recessive PD across the 3 disorders: PARK- can be found in the Supplementary Methods 1. Parkin, PARK-PINK1, and PARK-DJ1 (nomenclature according to the recommendations of the MDS Task Inclusion and Exclusion Criteria for Patients Force Classification and Nomenclature of Genetic and Genetic Variants Movement Disorders).4 Our group has recently devel- Because this review is limited to genes following oped and launched the Movement Disorder Society autosomal-recessive transmission, only patients carrying Genetic mutation database (MDSGene; http://www. 2 or more mutations in the same gene were included. mdsgene.org).5 MDSGene aims to provide a compre- Genetic variants across all 3 genes were part of our sys- hensive online resource linking reported genetic muta- tematic assessment. Variants were excluded if they had tions with movement disorder phenotypes and other a minor allele frequency (MAF)  1% based on the demographic and clinical information. This review fol- ethnicity with the maximal MAF in the ExAC Browser lows MDSGene’s standardized data extraction proto- (http://exac.broadinstitute.org), dbSNP (http://www. col optimized for hereditary movement disorders and ncbi.nlm.nih.gov/snp/), and/or in at least 100 unaf- (1) presents an overview on the currently available phenotypic and genotypic data on autosomal recessive fected control individuals screened for the variant of PD, (2) assesses the pathogenicity of reported poten- interest in the respective publication. Where available, tially causative mutations, (3) compares published clinical data were extracted for all mutation carriers data across the 3 genes and provides stratified analyses who had definite or probable PD designated as such in in selected patient subgroups, (4) evaluates the extent the respective publication or who were described to and potential impact of missing data on the interpreta- show bradykinesia and at least 1 additional cardinal tion of the results, and (5) identifies potential conse- parkinsonian sign, that is, resting tremor, rigidity, and quences for genetic counseling in clinical practice, as postural instability. This included patients originating well as resulting new research leads. from multiplex as well as simplex families. Methods Data Collection Process We applied the above-described MDSGene data MDSGene extraction protocol to all eligible articles. For each The literature search and data extraction protocol publication, data on demographic, genetic, and clinical have been developed for the generation and mainte- variables were extracted (see Supplementary Table 2 nance of MDSGene, a database that summarizes and for the list of extracted variables). Information was quantifies genetic and phenotypic data from the litera- obtained from the original or related (ie, previously or ture for hereditary movement disorders.5 Data col- subsequently published) articles referring to the same lected for this review have been posted on MDSGene patients. Phenotypic variables comprised clinical signs (available at http://www.mdsgene.org). and symptoms, levodopa response, and information on different motor and nonmotor scales. Physical loca- Literature Search and Eligibility Criteria tion, genomic, coding, and nomenclature as We performed a systematic literature search for pub- well as genotype and zygosity (genotype) were col- lications on PD patients with Parkin, PINK1, and DJ1 lected for all mutations. Missing nomenclature was mutations using the National Center for Biotechnol- curated from the given information wherever possible ogy Information’s PubMed database (https://www. using the Ensembl (http://www.ensembl.org/)6 and ncbi.nlm.nih.gov/pubmed) based on standardized Mutation Taster (http://www.mutationtaster.org/)7 data- search terms (Supplementary Table 1). An additional bases. All mutations were mapped to GRCh37/hg19, and search focusing on deep brain stimulation (DBS) used nomenclature was based on the transcripts Parkin the same search terms as above and added “DBS” OR ENST00000366898, PINK1 ENST00000321556, and “stimulation.” DJ1 ENST00000493678 (http://www.ensembl.org/).

Movement Disorders, Vol. 33, No. 5, 2018 731 KASTEN ET AL

Pathogenicity Scoring Results The degree of pathogenicity of a genetic variant was Articles and Study Types assessed by investigating its segregation with disease in the reported pedigrees, its frequency in controls, the The PubMed literature search yielded a total of corresponding Combined Annotation Dependent 3652 citations, among which 224 studies were eligi- Depletion (CADD) score (http://cadd.gs.washington. ble for data extraction on affected Parkin mutation edu/),8 as well as functional evidence extracted from carriers (151 studies), PINK1 (46 studies), and DJ1 published in-vitro and in-vivo studies. Based on these mutation carriers (27 studies); see Supplementary Fig- categories, a pathogenicity score was devised, and ure 1A. The most frequently included study types mutations were classified as definitely pathogenic included mutational screens (45%), family studies (score > 14), probably pathogenic (score 10-14), pos- (23%), or a combination of different designs (26%), sibly pathogenic (score 5-9), or benign (score < 5) among which the combination of mutational screens based on predefined criteria (see details in Supplemen- and family studies was the most common (54%). Sin- gle case reports and sib-pair studies were rare, repre- tary Methods 2). senting 4% and 3% of all studies, respectively. Review Articles Twenty-six percent of all included studies used spe- cific AAO ranges for patients’ ascertainment (applica- For comparison of the extracted data following ble to 331 of all 1127 included PD patients). MDSGene criteria with “common expert knowledge” Specifically searching the DBS literature yielded 97 about the phenotype of mutation carriers, we per- citations, 12 of which were eligible for data extrac- formed a systematic literature search for review tion on affected Parkin mutation carriers (12 studies), articles on Parkin, PINK1, and DJ1 using PubMed. PINK1 mutation carriers (3 studies but complete We applied the above-mentioned search terms (Supple- overlap with the 12 Parkin studies), and DJ1 muta- mentary Table 1) for reviews only, filtering for 2 dif- tion carriers (none). Overall, data were reported on ferent time frames, that is, recent reviews published in 43 patients, 42 of whom had mutations in the Parkin 2015-2017 and older review articles published in the and 1 of whom had a mutation in the PINK1 gene. third year after the discovery of each of the 3 genes In almost all studies clinical benefit of DBS was (2000 for Parkin, 2008 for PINK1, and 2004 for reported to be good or comparable to that observed DJ1). The latter period was chosen as a comprehen- in idiopathic PD. One study reported modest sive body of data had already become available 3 improvement after DBS in 3 patients, all of whom years after gene identification, and reviews at that had marked axial symptoms that did not improve, time tended to be more detailed than the more whereas other patients were reported to experience recently published ones. After exclusion of duplicate excellent improvement with DBS after a disease dura- articles resulting from our search strategy, we screened tion of as long as 30 years. all articles and extracted available clinical data. For an overview of the literature search as well as the fil- Included Patients, Pathogenicity of tering procedure, see Supplementary Figure 1B. A list Mutations, and Data Missingness of all included review articles can be found in Supple- A total of 2204 potentially eligible PD mutation car- mentary Methods 3 and 4 and the reported character- riers for which clinical and/or demographic informa- istics in Supplementary Table 3. tion were available were identified by our systematic literature screen and data extraction procedure. Of Statistical Analyses these, 1077 patients were excluded (1027 single het- All statistical analyses were performed using SPSS erozygous mutation carriers and 50 fulfilling other 22.0.0.1 (IBM, Armonk, NY). We compared continu- exclusion criteria), and a total of 1127 patients (ie, ous clinical and demographic data between groups of 958 Parkin, 139 PINK1, and 30 DJ1 mutation car- individuals using nonparametric tests, such as the riers) were included in the subsequent systematic anal- Kruskal-Wallis and Wilcoxon rank sum tests, as yses (Table 1). appropriate. Categorical data were analyzed between Across all 1127 included patients with causative groups using the chi-square test. For comparisons Parkin, PINK1,orDJ1 mutations, a total of 221 dif- regarding the median age at onset (AAO), statistical ferent mutations were found. Of these, 23% were imputations of missing data were made with the classified as definitely pathogenic, 68% as probably median of available data (at the gene level). We tested pathogenic, and 9% as possibly pathogenic. Although for possible correlation between the final pathogenicity missense mutations represented the most frequent score (sum of pathogenicity scores of all the mutations mutation type for PINK1 and DJ1 (47.6% and a single patient carried) and the AAO using Spearman 45.0%, respectively), Parkin mutations were pre- correlation coefficient. dominately structural variants (43.2%). Average 6

732 Movement Disorders, Vol. 33, No. 5, 2018 MDSGene REVIEW: Parkin, PINK1, DJ1

TABLE 1. Breakdown of number and type of mutations 27% of PINK1 mutation carriers, and 23% of DJ1 and numbers of patients mutation carriers (Fig. 1).

Number and type Number of of mutations Gene patients Phenotypic and Mutational Details by Gene

1 Hom. Parkin 510 Parkin PINK1 116 The 958 Parkin mutation carriers originated from DJ1 28 663 families. The proportion of men was 56%. The Total 654 1 Comp.-het. Parkin 418 majority of patients were of Asian ethnicity (39%), PINK1 23 followed by Caucasians and Hispanics (31% and DJ1 2 10%, respectively). Most patients originated from Iran Total 443 (14%), China (11%), Japan (10%), or Portugal (9%); 2 Hom. Parkin 7 PINK1 0 see Supplementary Figure 2. The median AAO of all DJ1 0 Parkin mutation carriers was 31 years (interquartile Total 7 range [IQR], 23-38 years), with the majority (62%) 1 Hom. 1 1 het. Parkin 16 showing early PD AAO (ie, 20-40 years), 22% a late PINK1 0 AAO (>40 years), and 16% a juvenile AAO (<20 DJ1 0 Total 16 years); see Supplementary Table 4 and Supplementary 1 Comp.-het. 1 1 het. Parkin 7 Figure 3A. PINK1 0 Detailed clinical information is summarized in Fig- DJ1 0 ure 2A. Information on bradykinesia, with 50% miss- Total 7 Reassigned mutational status Parkin 33 ing data, was the most consistently reported sign. For PINK1 12 noncardinal signs and symptoms, missingness ranged DJ1 5 from 73% to 97% (Table 2). With these caveats in Reassigned mutational status Total 50 mind, the following frequencies of symptoms and signs across all 958 Parkin patients were observed: In Hom., homozygous mutation (same mutation present on both alleles); Comp.-het., compound-heterozygous mutations (assuming different muta- tions present on both alleles of the same gene); Het., heterozygous muta- tion (1 mutation on 1 of the 2 alleles). Mutations and patients included in MDSGene are shaded in gray. Patients with a reassigned mutational status (highlighted in red) were excluded. Reasons for reassignment of mutations were heterozygous zygosity, benign pathogenicity status, discrepant information on the segregation, or unclear or inconsistent mutation nomenclature.

standard deviation (SD) CADD score (except for structural variants, for which CADD scores cannot be calculated easily; see Supplementary Methods 2 for details) of the resulting 78 different Parkin,50PINK1 and 18 DJ1 mutations was 29.3 6 7.7 (range, 2-46), 30.5 6 7.2 (range, 12-51), and 24.0 6 10.8 (range, 2- 50), respectively. Publications were screened for func- tional evidence of pathogenicity of mainly missense mutations, and such evidence was available for 19 of 26 different Parkin missense mutations (73%), for 20 of 24 PINK1 mutations (83%), and for 5 of 8 DJ1 mutations (63%). Mutations other than missense were mostly not further assessed because of their obvious (truncating) effect. A major challenge for this systematic review was the degree of missingness of phenotypic data. Missing data not only affected nonmotor signs and symptoms of all patients, but specific information was even often unavailable for cardinal motor signs (affecting 7%- 78% of the reported patients). Initial signs and symp- toms, that is, those present at the onset of the disease, FIG. 1. Percentage of missing clinical data for (A) cardinal motor and were provided for 12% of Parkin mutation carriers, (B) nonmotor signs and symptoms in Parkin, PINK1, and DJ1.

Movement Disorders, Vol. 33, No. 5, 2018 733 KASTEN ET AL

FIG. 2. Reported signs and symptoms in PD patients with (A) Parkin, (B) PINK1, and (C) DJ1 mutations. Signs and symptoms are listed according to their frequency in reported Parkin, PINK1, and DJ1 mutation carriers. only 3% (32 cases), atypical signs (eg, antecollis/retro- [24 cases]), cognitive decline was reported. Dystonia collis, pyramidal signs, spasticity, alien limb syndrome) 169 (18%), dyskinesia 19% (180 cases), and motor fluc- were reported, and for a comparable proportion (2.5% tuations (15% [146 cases]) were relatively common.

734 Movement Disorders, Vol. 33, No. 5, 2018 MDSGene REVIEW: Parkin, PINK1, DJ1

TABLE 2. Overview of reported signs and symptoms in Parkin, PINK1, and DJ1 mutation carriers: (A) motor and atypical signs and symptoms and (B) nonmotor signs and symptoms

A

Parkin PINK1 DJ1

Signs/symptoms Yes No Missing Yes No Missing Yes No Missing

Parkinsonism 958 (100%) 0 (0%) 0 (0%) 139 (100%) 0 (0%) 0 (0%) 30 (100%) 0 (0%) 0 (0%) Bradykinesia 470 (49%) 13 (1%) 475 (50%) 107 (77%) 5 (4%) 27 (19%) 27 (90%) 1 (3%) 2 (7%) Rigidity 259 (27%) 19 (2%) 680 (71%) 86 (62%) 6 (4%) 47 (34%) 21 (70%) 0 (0%) 9 (30%) Tremor 294 (31%) 26 (3%) 638 (66%) 72 (51%) 12 (9%) 55 (40%) 19 (63%) 5 (17%) 6 (20%) Postural instability 159 (17%) 50 (5%) 749 (78%) 36 (26%) 17 (12%) 86 (62%) 12 (40%) 5 (17%) 13 (43%) Dyskinesia 180 (19%) 48 (5%) 730 (76%) 54 (38%) 23 (17%) 62 (45%) 7 (23%) 4 (13%) 19 (64%) Dystonia 169 (18%) 90 (9%) 699 (73%) 29 (21%) 41 (30%) 69 (49%) 14 (46%) 5 (17%) 11 (37%) Hyperreflexia 53 (6%) 55 (6%) 850 (88%) 19 (14%) 31 (22%) 89 (64%) 4 (13%) 6 (20%) 20 (67%) Diurnal fluctuations 52 (5%) 19 (2%) 887 (93%) 11 (8%) 7 (5%) 121 (87%) 1 (3%) 3 (10%) 26 (87%) Sleep benefit 59 (6%) 22 (2%) 877 (92%) 16 (12%) 21 (15%) 102 (73%) 1 (3%) 0 (0%) 29 (97%) Motor fluctuations 146 (15%) 22 (2%) 790 (83%) 47 (34%) 11 (8%) 81 (58%) 4 (13%) 0 (0%) 26 (87%) Atypical 32 (3%) 63 (7%) 863 (90%) 3 (2%) 32 (23%) 104 (75%) 4 (13%) 8 (27%) 18 (60%) B

Parkin PINK1 DJ1

Signs/symptoms Yes No Missing Yes No Missing Yes No Missing

Nonmotor symptoms 124 (13%) 10 (1%) 824 (86%) 59 (42%) 4 (3%) 76 (55%) 17 (57%) 0 (0%) 13 (43%) Olfaction 16 (2%) 13 (1%) 929 (97%) 8 (6%) 8 (6%) 123 (88%) 0 (0%) 0 (0%) 30 (100%) Depression 43 (5%) 49 (5%) 866 (90%) 23 (17%) 18 (13%) 98 (70%) 4 (13%) 1 (3%) 25 (84%) Anxiety 27 (3%) 16 (2%) 915 (95%) 14 (10%) 12 (9%) 113 (81%) 4 (13%) 2 (7%) 24 (80%) Psychotic 22 (2%) 31 (3%) 905 (95%) 12 (9%) 30 (22%) 97 (69%) 6 (20%) 3 (10%) 21 (70%) Sleep disorder 38 (4%) 11 (1%) 909 (95%) 14 (10%) 3 (2%) 122 (88%) 3 (10%) 2 (7%) 25 (83%) Cognitive decline 24 (3%) 97 (10%) 837 (87%) 20 (14%) 55 (40%) 64 (46%) 5 (17%) 6 (20%) 19 (63%) Autonomic 35 (4%) 48 (5%) 875 (91%) 19 (14%) 23 (16%) 97 (70%) 4 (13%) 7 (23%) 19 (64%)

An overview of available data in mutation carriers about a selection of (A) motor and atypical signs and symptoms and (B) nonmotor signs and symptoms. Missing, no data about the specific sign/symptom is available; Yes, sign/symptom is reported; No, sign/symptom is not reported.

Looking more closely at dystonia, this symptom was missense mutations in 22.3% and frameshift mutations reported not to be L-dopa-induced in 78 cases (46% of in 16.5% (see Supplementary Fig. 5A). The most com- 171 patients with reported dystonia) and as L-dopa- mon mutation was c.(17111_172-1)_(41211_413- induced in 4 cases, and no information on the relation- 1)del, representing a deletion of exon 3 (Supplementary ship to L-dopa intake was given for 89 cases (52%). Fig. 6A; www.mdsgene.org; Parkin; filtered by “index Dyskinesia was reported to be L-dopa-induced in 123 of patients only”). Thirty-five of the 139 different 181 cases (68%), and information was missing for all sequence variants (25%) were classified as definitely remaining cases. Considering overall treatment response, pathogenic, 94 (68%) as probably pathogenic, and 10 the overwhelming majority of those with available infor- (7%) as possibly pathogenic, using the MDSGene path- mation (187 of 200 cases [94%]) had a good response. ogenicity scoring classification. A detailed overview of (Supplementary Fig. 4). the locations of mutations alongside their pathogenicity A total of 139 different disease-causing sequence var- status in the Parkin gene is depicted in Figure 3A and iants were reported in the Parkin gene. 53.2% of all the Parkin protein in Supplementary Figure 7A. patients (510 patients) carried a homozygous mutation, Of the 510 homozygous Parkin mutation carriers, and 43.6% (418 patients) were likely compound- 395 (77%) carried definitely pathogenic mutations, heterozygous (specific information on zygosity was 112 (22%) probably pathogenic mutations, and rarely provided). Seven patients (0.7%) had 2 homozy- 3 (1%) possibly pathogenic mutations. For the gous mutations, 16 patients (1.7%) had a homozygous 418 compound-heterozygous mutation carriers, a com- and a heterozygous mutation, and 7 patients (0.7%) bination of pathogenicity scores including 1 definitely had a compound-heterozygous mutation, as well as an pathogenic sequence variant (165 cases; 40%) was additional heterozygous mutation. A total of 1350 most frequent. sequence variants reported in index patients fell into We performed an additional analysis differentiating the following mutation classes: structural variants, the patients with possibly or definitely pathogenic muta- most common mutation type, in 43.2%; followed by tions. For this, we grouped biallelic mutation carriers

Movement Disorders, Vol. 33, No. 5, 2018 735 KASTEN ET AL into those harboring at least 1 possibly pathogenic a late, and 15% a juvenile PD AAO (Supplementary mutation versus those with 2 definitely pathogenic Table 4 and Supplementary Fig. 3B). mutations. Carriers of possibly pathogenic mutations A complete listing of the frequencies of signs and had an AAO of 30 6 9 years and carriers of definitely symptoms in PINK1 patients is depicted in Figure 2B. pathogenic mutations an AAO of 31 6 12 years (P 5 Information on the cardinal sign bradykinesia was 0.769, Mann-Whitney test). The frequencies of rest most complete (19% missing data), but missing data tremor (P 5 0.707), dystonia (P 5 0.598), and cogni- ranged from 45% to 88% for noncardinal signs and tive decline (P 5 0.754) were comparable between symptoms (Table 2). With these caveats in mind, the groups. Because of relatively small frequencies of following frequencies of symptoms and signs across all PINK1 and DJ1 mutation carriers, this analysis was 139 PINK1 patients were observed: dyskinesia was only carried out for Parkin. reported in 39% (54 cases), dystonia in 21% (29 cases), and motor fluctuations in 34% (47 cases) of PINK1 the included patients. Dyskinesia were reported to be The 139 PINK1 mutation carriers originated from L-dopa-induced in 85% (46 cases) and not L-dopa- 85 families. The proportion of men was 42%. The induced in 1 case, and information was missing in 7 majority of patients were of Caucasian ethnicity cases. Dystonia was reported to be L-dopa-induced in (33%), followed by mixed/others (31%) and Asian 7 cases (24%) and not L-dopa-induced in 17 cases (18%) mixed/other ethnicity (34%), followed by Cau- (59%), and information was missing in 5 cases (17%). casians and Asians (26% each). Most patients origi- Cognitive decline (14% [20 cases]) and psychotic nated from Italy (20%), Iran (10%), or Spain (8%); symptoms (9% [12 cases]) were reported in a small see Supplementary Figure 8. The median AAO of all fraction of all PINK1 patients. Similar to Parkin PINK1 mutation carriers was 32 years (IQR, 25-39 mutation carriers, the vast majority (99% of 85 cases) years), with the majority (62%) having an early, 22% of those with a reported levodopa response showed a

FIG. 3. Schematic representation of the (A) Parkin, (B) PINK1, and (C) DJ1 genes and mutations listed in MDSGene.

736 Movement Disorders, Vol. 33, No. 5, 2018 MDSGene REVIEW: Parkin, PINK1, DJ1

FIG. 3. Continued

good response to levodopa treatment (Supplementary mutations with their pathogenicity status in the Fig. 4). PINK1 gene is illustrated in Figure 3B and PINK1 A total of 62 different disease-causing sequence var- protein in Supplementary Figure 7B. iants were reported in the PINK1 gene. Eighty-three Of the 116 homozygous PINK1 mutation carriers, percent of all patients carried a homozygous mutation, 69 cases (59.5%) had probably, 45 (38.8%) definitely, and 17% were compound-heterozygous. The total of and 2 possibly (1.7%) pathogenic mutations. Of the 100 sequence variants reported in index patients fell 23 compound-heterozygous cases, 19 (83%) had a into the following mutation classes: missense muta- combination of 2 probably pathogenic mutations, and tions, the most frequent type, in 47.6%, followed there was 1 case each (4%) with a combination of 2 by structural variants in 19.1% and nonsense muta- possibly, 1 possibly and 1 probably, 1 probably and 1 tions in 14.3% (Supplementary Fig. 5B). The most fre- definitely, and 2 definitely pathogenic mutations. quent mutation of all was the missense mutation c.1040T>C, resulting in an amino acid change of leu- cine to proline at position 347 (Supplementary Fig. DJ1 6B; www.mdsgene.org; PINK1; filtered by “index The 30 DJ1 mutation carriers originated from 18 patients only”). Of 62 different mutations, 13 (21%) families, with 76% male. Because of the relatively were classified as definitely pathogenic, 44 (71%) as small number of reported DJ1 mutation carriers, com- probably pathogenic, and 5 (8%) as possibly patho- parisons of frequencies for genetic and clinical charac- genic. A detailed overview of the location of all teristics should be interpreted with care. The ethnicity

Movement Disorders, Vol. 33, No. 5, 2018 737 KASTEN ET AL of patients was mixed/other (38%), Asian (25%), His- panic, Ashkenazi Jewish and Caucasian (13% each). Most patients originated from Italy, Iran (25% each), or Turkey (18%); see Supplementary Figure 9. The median AAO of all patients was 27 years (IQR, 22-35 years), with the majority (83%) having an early, 13% a juvenile, and 4% a late AAO of PD; see Supplemen- tary Table 4 and Supplementary Figure 3C. Concerning clinical data, the most comprehensive information was provided for the cardinal sign brady- kinesia (7% missing data). Dystonia was reported to be present in 46% of patients (14 cases), dyskinesia in 23% (7 cases), hyperreflexia in 13% (4 cases), cogni- tive decline in 17% (5 cases), and psychotic symptoms in 20% (6 cases) in less than a quarter of the patients (Table 3). Dystonia was reported to be present in 14 cases, 2 of those were reported to be L-dopa induced, 9 not to be L-dopa induced and in 2 cases this was unspecified. Dyskinesia was reported to be L-dopa- induced in 5 of 7 cases, and in 2 case information was missing. A complete listing of the frequencies of indi- vidual signs and symptoms is depicted in Figure 2C. Forty-five percent of those with reported treatment response (5 of 11 cases) responded well to L-dopa (Supplementary Fig. 4). A total of 20 different disease-causing sequence var- iants were reported in the DJ1 gene. Ninety-three per- cent of all patients carried a homozygous mutation, and 7% were compound-heterozygous. The total of 20 sequence variants reported in index patients fell into the following mutation classes: missense changes in 45%, followed by splice-site mutation in 15% and structural FIG. 4. Bar diagrams of (A) motor and atypical signs and symptoms variants and frameshifts in 10% each (Supplementary and (B) nonmotor signs and symptoms in Parkin, PINK1, and DJ1 Figure 5C). All index patients carried a different muta- mutation carriers. tion (Supplementary Fig. 6C; www.mdsgene.org; DJ1; filtered by “index patients only”). Of 20 different muta- Parkin mutation carriers and 42% of PINK1 mutation tions, 4 (20%) were classified as definitely pathogenic, carriers. 12 (60%) as probably pathogenic, and 4 (20%) as pos- Table 2 and Figure 2 provide a detailed overview on sibly pathogenic. A detailed overview of the location of the clinical signs and symptoms and their availability all mutations with their pathogenicity status in the DJ1 for all genes. Focusing on the reported clinical signs gene is illustrated in Figure 3C and the DJ1 protein in and symptoms and, for this purpose, considering miss- Supplementary Figure 7C. ing data in noncardinal signs and symptoms as Of the 28 homozygous DJ1 mutation carriers, 19 absence of the respective phenotype resulted in the fol- (68%) had a probably pathogenic mutation, 7 (25%) lowing observations. The most frequently reported a definitely mutation, and 2 (7%) a possibly patho- noncardinal signs and symptoms across all 1127 genic mutation. The 2 compound-heterozygous cases included patients were dyskinesia (19%-38%), dysto- had a combination of 1 possibly and 1 probably path- nia (18%-46%), and motor fluctuations (13%-34%); ogenic mutations. see Figure 4 for a summary of detailed signs and symptoms reported for all included patients with Par- Comparison of Demographic and Clinical kin, PINK1,orDJ1 mutations. In the motor domain, Characteristics of Mutation Carriers dyskinesia (38%) and motor fluctuations (34%) were Across Genes most commonly reported for PINK1 PD patients, Comparing the overall sex distribution, a significant whereas dystonia (46%), tremor (63%), and atypical difference was found across the 3 genes (P 5 0.0046), signs (13%) were most commonly reported in DJ1 PD with the proportion of men being greatest in the DJ1 patients (Table 2). In contrast, atypical signs were mutation carriers (76%), compared with 56% of very rarely reported as present in Parkin (3%) and

738 Movement Disorders, Vol. 33, No. 5, 2018 MDSGene REVIEW: Parkin, PINK1, DJ1

FIG. 5. Comparison of comments on AAO and L-dopa responsiveness from review articles with actual data available in the MDSGene database. Pie chart(s) in inner circle display percentages of AAO and L-dopa responsiveness reported in articles represented in MDSGene. The outer ring provides percentage of review articles considering AAO and L-dopa responsiveness of Parkin, PINK1,orDJ1 mutation carriers.

PINK1 (2%) mutation carriers. In the nonmotor articles and MDSGene data. Although almost half the domain, Parkin mutation carriers were by far the least Parkin review articles mention juvenile AAO as char- affected (13%), whereas DJ1 mutation carriers were acteristic of mutations in this gene, only a minority of reported to have the highest percentage (57%) of non- Parkin mutation carriers actually had juvenile onset in motor symptoms overall. the MDSGene data. Regarding the L-dopa response, To test whether mutations with a potential higher reviews and MDSGene data match well for Parkin functional impact on gene function lead to an earlier (47% “yes” for reviews vs 41% “yes” for MDSGene). onset of PD, we tested for a possible correlation of the However, only about a quarter of the review articles pathogenicity score and AAO, which was nonsignifi- consider L-dopa responsiveness a hallmark of PINK1 cant, however (Parkin, r 5 0.030, P 5 0.386; PINK1, or DJ1, whereas MDSGene data show a similarly high r 5 0.072, P 5 0.427; and DJ1, r 5 0.112, P 5 response proportion for PINK1 and DJ1 mutation 0.603, using Spearman correlation). carriers as for Parkin mutation carriers. Detailed com- parisons for clinical signs and symptoms are schemati- Comparison of Phenotypic Information in cally represented in Supplementary Figure 10B. Previously Published Review Articles With MDSGene Data Discussion A total of 36 review articles were included in this comparison, comprising 11 articles published in the This is the first article of the MDSGene series pro- past 3 years and 25 published in the third year after viding a comprehensive and up-to-date review of the the discovery of Parkin, PINK1, and DJ1 as causative published peer-reviewed literature on Parkin, PINK1, for PD. Supplementary Figure 10A provides an over- and DJ1 mutation carriers in the English language. It view on the frequency of reviews that reported certain is based on fully curated clinical and mutation data; phenotypic features as typical for mutations in the 3 data extraction follows a stringent standard operating genes. Overall, early AAO, L-dopa responsiveness, procedure specifically developed for MDSGene. An slow disease progression, and dystonia are the most additional novel feature of this review is that it pro- commonly mentioned clinical characteristics across all vides full data access at the patient and mutation lev- reviews. L-Dopa responsiveness, slow disease progres- els, as well as at the level of summary statistics, with sion, sleep benefit, dyskinesias, and hyperreflexia are various data-filtering options via the MDSGene online predominantly considered “typical” of Parkin muta- database. In light of the ever-increasing number of tions; absence of cognitive decline is mentioned for published articles and new journals, the present review both Parkin and PINK1 mutations. Figure 5 compares thus addresses an important unmet need and is based information on AAO and L-dopa between the review on data from >1100 patients with recessively

Movement Disorders, Vol. 33, No. 5, 2018 739 KASTEN ET AL inherited PD from 220 different disease-causing including early onset of an overall clinically typical mutations in Parkin, PINK1,orDJ1. form of PD with excellent treatment response and Possibly the most important and also alarming find- with dystonia and dyskinesia being relatively common ing of the present review is the proportion of missing and cognitive decline relatively uncommon. Although phenotypic data. The lack of a detailed description of dystonia appeared to be mostly independent of L-dopa individual phenotypic features was found to be the intake, dyskinesias were most commonly reported to rule rather than the exception. Adding an additional be treatment-induced. Another commonly held notion layer of complexity, missingness will likely be nonran- and well-known clinical observation in the context of dom. When signs and symptoms are viewed in the recessive PD is its slow(er) progression compared with clinical context, missing data will likely represent idiopathic PD.9 In this context, one should note that “symptom or sign present” in cases of very frequent we were unable to extract data on disease progression symptoms, such as the cardinal motor sign bradykine- from the available literature, as it is reported in an sia, which is likely present in the vast majority of entirely nonsystematic and unquantified fashion. Such patients but not necessarily mentioned in the pub- observations can only be made in the setting of large, lished reports. In contrast, “symptom or sign absent” multicenter longitudinal studies combining subject- is the presumably more likely interpretation of missing level data on several hundred patients with recessive data in case of more infrequent and/or more apparent PD in a standardized fashion. Because of the broad or unusual symptoms or signs, such as psychosis or phenotypic overlap across carriers of mutations in the cognitive decline. However, complicating matters fur- recessive PD genes, the rarity of reported DJ1 muta- ther, in the latter scenario, it cannot be excluded that tions, and the overall data gaps, it is also currently unusual symptoms or signs or subtle presentations not possible to conclusively tease out any clinical “red were not evaluated. Supplementary Figure 11 visual- flags” that might help to identify patients with a muta- izes the effect that differential interpretation of missing tion in a specific gene on clinical grounds. Indeed, it is data has on the frequency of certain clinical signs and often even difficult to distinguish Parkin, PINK1, and symptoms using bradykinesia and psychotic symptoms DJ1 mutation carriers from those with mutations in as examples. These resulting striking differences in other PD genes, such as LRRK210 or even with idio- potential frequencies of specific phenotypic features pathic PD. In addition, there is marked phenotypic are not only of methodologic interest but of great clin- overlap with some forms of dystonia-parkinsonism, ical importance, as they could inform genetic counsel- such as dopa-responsive dystonia.11 ing if the data were more robust. Given these large Interestingly, when comparing actual data with data gaps, unfortunately, any conclusions on pheno- “common expert knowledge” put forward in the pub- typic manifestations and variability of clinical features lished reviews, we detected several discrepancies: For across genes and mutations can currently be drawn example, although almost half of all reviews consider only tentatively at best which urgently calls for “next- Parkin-linked PD a juvenile-onset disorder, only about generation phenotyping.”1 Indeed, in contrast to clini- a seventh of the reported patients had juvenile onset, cal data reporting, the genetic analysis of patients with whereas almost a quarter presented with a late AAO > parkinsonism has markedly improved over the past 2 40 years (Fig. 5), which, on the other hand, is not men- decades since the description of the first recessive PD tioned as typical in any of the published reviews. gene, Parkin, in 2000.1 However, despite these advan- Another example is sleep benefit, which is considered a ces in molecular genetic analyses and the international characteristic feature in a quarter of the reviews but standard of describing mutations via reported in the original articles for a minute fraction of Variation Society nomenclature, genetic data were fre- Parkin mutation carriers only (Supplementary Fig. quently reported in an unstandardized or even incor- 10B), although, of course, this does not exclude that rect way, leading to the adaptation to current there actually is sleep benefit. These observations nomenclature in a large proportion of mutations, espe- underline the need for standardized reporting on mono- cially of those reported in the late 1990s and early genic movement disorder patients, such as recessive PD 2000s, or even exclusion of a small fraction for the patients. Systematic and comprehensive reviews such as present review as part of the genetic data curation ours can help to identify various biases including that process. Finally, it is important to keep in mind that of continued reporting (or omission) of clinical features the current literature on recessive PD is expected to be considered typical in early reports and thus having fraught with publication and selective reporting bias, become entrenched in the literature. as, for example, caused by the likely overreporting of Based on the results of this first MDSGene review, “novel,” private mutations and/or of unusual pheno- we would like to draw the following conclusions on typic characteristics. genetic testing recommendations, reporting of muta- The MDSGene review of recessive PD does recapitu- tion carriers, and future research needs. (1) A PD age late many of the previously described findings of onset < 40 years should raise a red flag for the

740 Movement Disorders, Vol. 33, No. 5, 2018 MDSGene REVIEW: Parkin, PINK1, DJ1 presence of Parkin, PINK1,orDJ1 mutations. (2) It is 4. Marras C, Lang A, van de Warrenburg BP, et al. Nomenclature of genetic movement disorders: Recommendations of the international currently impossible to identify mutation carriers in Parkinson and movement disorder society task force. Mov Disord one of these genes on clinical grounds; thus, when 2016;31(4):436-457. genetic testing is performed, we would recommend 5. Lill CM, Mashychev A, Hartmann C, et al. Launching the move- ment disorders society genetic mutation database (MDSGene). offering a PD gene panel including at least all 3 of Mov Disord 2016;31(5):607-609. these genes to PD patients with an age of onset < 40 6. Yates A, Akanni W, Amode MR, et al. Ensembl 2016. Nucleic years and/or a suggestive family history (unaffected Acids Res 2016;44(D1):D710-D716. parents but affected siblings). In case of unavailability 7. Schwarz JM, Cooper DN, Schuelke M, Seelow D. Muta- tionTaster2: mutation prediction for the deep-sequencing age. Nat of a panel, one could start with testing Parkin,asthis Methods 2014;11(4):361-362. is the most frequently affected gene. (3) Data missing- 8. Kircher M, Witten DM, Jain P, et al. A general framework for esti- ness is a profoundly underestimated problem to the mating the relative pathogenicity of human genetic variants. Nat extent that meaningful phenotype-genotype relation- Genet 2014;46(3):310-315. 9. Gaudet P, Michel P-A, Zahn-Zabal M, et al. The neXtProt knowl- ships based on the combination of published data are edgebase on human : 2017 update. Nucleic Acids Res currently largely impossible. Thus, systematic reporting 2017;45(D1):D177-D182. of phenotypes is a pressing need in light of increasingly 10. Mandemakers W, Morais VA, De Strooper B. A cell biological per- spective on mitochondrial dysfunction in Parkinson disease and available molecular genetic testing and the emergence other neurodegenerative diseases. J Cell Sci 2007;120(Pt 10):1707- of first gene-specific therapies entering clinical trials. (4) 1716. We propose to employ MDSGene as the basis for the 11. Lohmann E, Periquet M, Bonifati V, et al. How much phenotypic systematic collection of curated clinical and genetic variation can be attributed to parkin genotype? Ann Neurol 2003; 54(2):176-185. information on inherited movement disorders. 12. Healy DG, Falchi M, O’Sullivan SS, et al. Phenotype, genotype, and worldwide genetic penetrance of LRRK2-associated Parkin- Acknowledgments: We thank Andriy Machychev for database pro- son’s disease: a case-control study. Lancet Neurol 2008;7(7):583- gramming, the details of which will be reported elsewhere. 590. 13. Tadic V, Kasten M, Bruggemann€ N, Stiller S, Hagenah J, Klein C. Dopa-responsive dystonia revisited: diagnostic delay, residual References signs, and nonmotor signs. Arch Neurol 2012;69(12):1558- 1562. 1. Grunewald€ A, Kasten M, Ziegler A, Klein C. Next generation phe- notyping using the Parkin example: time to catch up with genetics. JAMA Neurol2013;70(9):1186-1191. 2. Kasten M, Weichert C, Lohmann K, Klein C. Clinical and demo- Supporting Data graphic characteristics of PINK1 mutation carriers--a meta-analy- sis. Mov Disord 2010;25(7):952-954. Additional Supporting Information may be found in 3. Puschmann A. Monogenic Parkinson’s disease and parkinsonism: clinical phenotypes and frequencies of known mutations. Parkin- the online version of this article at the publisher’s sonism Relat Disord 2013;19(4):407-415. web-site.

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