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Pre-clinical markers of Parkinson's Disease (PD) are needed, and to be relevant in pre-clinical disease, they should be quantifiably abnormal in early disease as well. Handwriting is impaired early in PD and can be evaluated using computerized analysis of drawn spirals, capturing kinematic, dynamic, and spatial abnormalities and calculating indices that quantify motor performance and disability. Digitized spiral drawing correlates with motor scores and may be more sensitive in detecting early changes than subjective ratings. However, whether changes in spiral drawing are abnormal compared with controls and whether changes are detected in early PD are unknown. 138 PD subjects (50 with early PD) and 150 controls drew spirals on a digitizing tablet, generating x, y, z (pressure) data-coordinates and time. Derived indices corresponded to overall spiral execution (severity), shape and kinematic irregularity (second order smoothness, first order zero-crossing), tightness, mean speed and variability of spiral width. Linear mixed effect adjusted models comparing these indices and cross-validation were performed. Receiver operating characteristic analysis was applied to examine discriminative validity of combined indices. All indices were significantly different between PD cases and controls, except for zero-crossing. A model using all indices had high discriminative validity (sensitivity = 0.86, specificity = 0.81). Discriminative validity was maintained in patients with early PD. Spiral analysis accurately discriminates subjects with PD and early PD from controls supporting a role as a promising quantitative biomarker. Further assessment is needed to determine whether spiral changes are PD specific compared with other disorders and if present in pre-clinical PD.

The Parkinson's Progression Markers Initiative (PPMI) is an ongoing observational, longitudinal cohort study of participants with Parkinson's disease, healthy controls, and carriers of the most common Parkinson's disease-related genetic mutations, which aims to define biomarkers of Parkinson's disease diagnosis and progression. All participants are assessed annually with a battery of motor and non-motor scales, 123-I Ioflupane dopamine transporter (DAT) imaging, and biological variables. We aimed to examine whether non-manifesting carriers of LRRK2 and GBA mutations have prodromal features of Parkinson's disease that correlate with reduced DAT binding. This cross-sectional analysis is based on assessments done at enrolment in the subset of non-manifesting carriers of LRRK2 and GBA mutations enrolled into the PPMI study from 33 participating sites worldwide. The primary objective was to examine baseline clinical and DAT imaging characteristics in non-manifesting carriers with GBA and LRRK2 mutations compared with healthy controls. DAT deficit was defined as less than 65% of putamen striatal binding ratio expected for the individual's age. We used t tests, χ2 tests, and Fisher's exact tests to compare baseline demographics across groups. An inverse probability weighting method was applied to control for potential confounders such as age and sex. To account for multiple comparisons, we applied a family-wise error rate to each set of analyses. This study is registered with ClinicalTrials.gov, number NCT01141023. Between Jan 1, 2014, and Jan 1, 2019, the study enrolled 208 LRRK2 (93% G2019S) and 184 GBA (96% N370S) non-manifesting carriers. Both groups were similar with respect to mean age, and about 60% were female. Of the 286 (73%) non-manifesting carriers that had DAT imaging results, 18 (11%) LRRK2 and four (3%) GBA non-manifesting carriers had a DAT deficit. Compared with healthy controls, both LRRK2 and GBA non-manifesting carriers had significantly increased mean scores on the Movement Disorders Society Unified Parkinson's Disease Rating Scale (total score 4·6 [SD 4·4] healthy controls vs 8·4 [7·3] LRRK2 vs 9·5 [9·2] GBA, p<0·0001 for both comparisons) and the Scale for Outcomes for PD – autonomic function (5·8 [3·7] vs 8·1 [5·9] and 8·4 [6·0], p<0·0001 for both comparisons). There was no difference in daytime sleepiness, anxiety, depression, impulsive–compulsive disorders, blood pressure, urate, and rapid eye movement (REM) behaviour disorder scores. Hyposmia was significantly more common only in LRRK2 non-manifesting carriers (69 [36%] of 194 healthy controls vs 114 [55%] of 208 LRRK2 non-manifesting carriers; p=0·0003). Finally, GBA but not LRRK2 non-manifesting carriers showed increased DAT striatal binding ratios compared with healthy controls in the caudate (healthy controls 2·98 [SD 0·63] vs GBA 3·26 [0·63]; p<0·0001), putamen (2·15 [0·56] vs 2·48 [0·52]; p<0·0001), and striatum (2·56 [0·57] vs 2·87 [0·55]; p<0·0001). Our data show evidence of subtle motor and non-motor signs of Parkinson's disease in non-manifesting carriers compared with healthy controls that can precede DAT deficit. Longitudinal data will be essential to confirm these findings and define the trajectory and predictors for development of Parkinson's disease. Michael J Fox Foundation for Parkinson's Research.

Mutations in THAP1 were recently identified as the cause of DYT6 primary dystonia; a founder mutation was detected in Amish–Mennonite families, and a different mutation was identified in another family of European descent. To assess more broadly the role of this gene, we screened for mutations in families that included one family member who had early-onset, non-focal primary dystonia. We identified 36 non- DYT1 multiplex families in which at least one person had non-focal involvement at an age of onset that was younger than 22 years. All three coding exons of THAP1 were sequenced, and the clinical features of individuals with mutations were compared with those of individuals who were negative for mutations in THAP1. Genotype–phenotype differences were also assessed. Of 36 families, nine (25%) had members with mutations in THAP1, and most were of German, Irish, or Italian ancestry. One family had the Amish–Mennonite founder mutation, whereas the other eight families each had novel, potentially truncating or missense mutations. The clinical features of the families with mutations conformed to the previously described DYT6 phenotype; however, age at onset was extended from 38 years to 49 years. Compared with non-carriers, mutation carriers were younger at onset and their dystonia was more likely to begin in brachial, rather than cervical, muscles, become generalised, and include speech involvement. Genotype–phenotype differences were not found. Mutations in THAP1 underlie a substantial proportion of early-onset primary dystonia in non- DYT1 families. The clinical features that are characteristic of affected individuals who have mutations in THAP1 include limb and cranial muscle involvement, and speech is often affected. Dystonia Medical Research Foundation; Bachmann–Strauss Dystonia and Parkinson Foundation; National Institute of Neurological Disorders and Stroke; Aaron Aronov Family Foundation.

Laurie Ozelius and colleagues identify mutations in THAP1 in families with a mixed type (DYT6) of primary torsion dystonia, a movement disorder characterized by twisting movements and abnormal posture. We report the discovery of a mutation in the THAP1 gene in three Amish-Mennonite families with mixed-onset primary torsion dystonia (also known as DYT6 dystonia). Another mutation in a German family with primary torsion dystonia suggests that THAP1 mutations also cause dystonia in other ancestry groups. We demonstrate that the missense mutation impairs DNA binding, suggesting that transcriptional dysregulation may contribute to the phenotype of DYT6 dystonia.

Laurie Ozelius and colleagues identify mutations in GNAL in families with primary torsion dystonia, a movement disorder characterized by repetitive twisting muscle contractions and postures. GNAL encodes Gα olf , a stimulatory G protein α subunit. Dystonia is a movement disorder characterized by repetitive twisting muscle contractions and postures 1 , 2 . Its molecular pathophysiology is poorly understood, in part owing to limited knowledge of the genetic basis of the disorder. Only three genes for primary torsion dystonia (PTD), TOR1A (DYT1) 3 , THAP1 (DYT6) 4 and CIZ1 (ref. 5 ), have been identified. Using exome sequencing in two families with PTD, we identified a new causative gene, GNAL , with a nonsense mutation encoding p.Ser293* resulting in a premature stop codon in one family and a missense mutation encoding p.Val137Met in the other. Screening of GNAL in 39 families with PTD identified 6 additional new mutations in this gene. Impaired function of several of the mutants was shown by bioluminescence resonance energy transfer (BRET) assays.

Dystonia is a movement disorder with many presentations and diverse causes. A systematic approach to dystonia helps to ensure that patients with this disorder receive optimum care. This Review begins with a summary of the clinical features of dystonia, followed by a discussion of other disorders to be considered and excluded before assigning the diagnosis of dystonia. Next, we emphasise the importance of classifying dystonia along several dimensions, and we explain how doing so aids in narrowing the differential diagnosis. The more common forms of dystonia are discussed in detail. Finally, we describe how to apply the clinical information for selection of appropriate laboratory investigations.

To the Editor: Most cases of Parkinson's disease are considered sporadic and idiopathic, although there is evidence of familial aggregation, and several monogenic forms have been identified. 1 Recently, several pathogenic mutations in the highly conserved leucine-rich repeat kinase 2 gene ( LRRK2 ) have been associated with autosomal dominant, late-onset Parkinson's disease. 1 Of these, the G2019S substitution is the most frequently reported. 2 It occurs in about 1 percent of unselected cases and 3 to 6 percent of familial cases of Parkinson's disease in persons primarily of European ancestry 2 but in 7 of 17 cases of familial disease in persons from . . .

Despite a hypothesis that harboring a leucine-rich repeat kinase 2(LRRK2) G2019S variation and a glucocerebrosidase (GBA) variant would have a combined deleterious association with disease pathogenesis, milder clinical phenotypes have been reported in dual LRRK2 and GBA variations Parkinson disease (PD) than in GBA variation PD alone. To evaluate the association of LRRK2 G2019S and GBA variants with longitudinal cognitive and motor decline in PD. This longitudinal cohort study of continuous measures in LRRK2 PD, GBA PD, LRRK2/GBA PD, and wild-type idiopathic PD used pooled annual visit data ranging from 2004 to 2019 from the Mount Sinai Beth Israel, Parkinson Disease Biomarker Program, Harvard Biomarkers Study, Ashkenazi Jewish-LRRK2-Consortium, Parkinson Progression Marker Initiative, and SPOT-PD studies. Patients who were screened for GBA and LRRK2 variations and completed either a motor or cognitive assessment were included. Data were analyzed from May to July 2020. The associations of LRRK2 G2019S and GBA genotypes on the rate of decline in Montreal Cognitive Assessment (MoCA) and Movement Disorders Society-Unified Parkinson Disease Rating Scale-Part III scores were examined using linear mixed effects models with PD duration as the time scale. Among 1193 individuals with PD (mean [SD] age, 66.6 [9.9] years; 490 [41.2%] women), 128 (10.7%) had GBA PD, 155 (13.0%) had LRRK2 PD, 21 (1.8%) had LRRK2/GBA PD, and 889 (74.5%) had idiopathic PD. Patients with GBA PD had faster decline in MoCA than those with LRRK2/GBA PD (B [SE], -0.31 [0.09] points/y; P < .001), LRRK2 PD (B [SE], -0.33 [0.09] points/y; P < .001), or idiopathic PD (B [SE], -0.23 [0.08] points/y; P = .005). There was a LRRK2 G2019S × GBA interaction in MoCA decline (B [SE], 0.22 [0.11] points/y; P = .04), but not after excluding severe GBA variations (B [SE], 0.12 [0.11] points/y; P = .28). Patients with GBA PD had significantly worse motor progression compared with those with idiopathic PD (B [SE], 0.49 [0.22] points/y; P = .03) or LRRK2 PD (B [SE], 0.77 [0.26] points/y; P = .004). These findings suggest that longitudinal cognitive decline in patients with GBA PD was more severe than in those with LRRK2/GBA PD, which more closely resembled LRRK2 PD. This further supports the notion of a dominant association of LRRK2 on GBA in individuals who carry both and raises the possibility of an LRRK2 × GBA interaction. However, the biological basis of a dominant association or interaction is not clear and is apparently contrary to basic investigations. Study of a larger cohort of individuals with severe GBA variation is warranted.

Identification of early changes in Dopamine-Transporter (DaT) SPECT imaging expected in the prodromal phase of Parkinson's disease (PD), are usually overlooked. Carriers of the G2019S LRRK2 mutation are known to be at high risk for developing PD, compared to non-carriers. In this work we aimed to study early changes in Dopamine uptake in non-manifesting PD carriers (NMC) of the G2019S LRRK2 mutation using quantitative DaT-SPECT analysis and to examine the potential for early prediction of PD. Eighty Ashkenazi-Jewish subjects were included in this study: eighteen patients with PD; thirty-one NMC and thirty-one non-manifesting non-carriers (NMNC). All subjects underwent a through clinical assessment including evaluation of motor, olfactory, affective and non-motor symptoms and DaT-SPECT imaging. A population based DaT-SPECT template was created based on the NMNC cohort, and data driven volumes-of-interest (VOIs) were defined. Comparisons between groups were performed based on VOIs and voxel-wise analysis. The striatum area of all three cohorts was segmented into four VOIs, corresponding to the right/left dorsal and ventral striatum. Significant differences in clinical measures were found between patients with PD and non-manifesting subjects with no differences between NMC and NMNC. Significantly lower uptake (p<0.001) was detected in the right and left dorsal striatum in the PD group (2.2±0.3, 2.3±0.4) compared to the NMC (4.2±0.6, 4.3±0.5) and NMNC (4.5±0.6, 4.6±0.6), and significantly (p = 0.05) lower uptake in the right dorsal striatum in the NMC group compared to NMNC. Converging results were obtained using voxel-wise analysis. Two NMC participants, who later phenoconverted into PD, demonstrated reduced uptake mainly in the dorsal striatum. No significant correlations were found between the DaT-SPECT uptake in the different VOIs and clinical and behavioral assessments in the non-manifesting groups. This study shows the clinical value of quantitative assessment of DaT-SPECT imaging and the potential for predicting PD by detection of dopamine depletion, already at the pre-symptomatic stage. Clinical registration numbers: NCT01089270 and NCT01089283.

Carbidopa-levodopa has been used for more than 50 years in the treatment of Parkinson disease (PD) and other movement disorders. Pyridoxal 5′-phosphate (PLP), an active form of vitamin B6 (pyridoxine), is involved in the decarboxylation of levodopa to dopamine; carbidopa, which is combined with levodopa to reduce peripheral levodopa conversion and minimize peripheral dopamine side effects, binds irreversibly with PLP. As a result, carbidopa-levodopa may cause vitamin B6 deficiency and associated sequelae, including seizures, especially in high doses. A 78-year-old gentleman with a 6-year history of PD on carbidopa-levodopa therapy and recent weight loss presented with new-onset myoclonus and focal to bilateral tonic-clonic seizures. Workup for vascular, infectious, malignant, metabolic, and autoimmune causes of seizure was unrevealing. The folate level was critically low at <2.20 ng/dL. Video EEG studies showed moderate cerebral dysfunction and seizures with diffuse onsets. Several anti-seizure medications (ASMs) were unsuccessfully tried, so empiric treatment with high-dose steroids was initiated eventually alongside intravenous vitamin B6 therapy. Following introduction of these interventions, the patient had no further epileptic events. The vitamin B6 level came back as undetectable at <1 μg/dL. The patient was discharged to a rehabilitation center for improved strength and function. At the time of writing, he remained on two ASMs as well as IV B6 supplementation. Vitamin B6 is a required cofactor in the decarboxylation of levodopa to dopamine, and high levodopa dosages may cause B6 deficiency; in addition, carbidopa binds B6 irreversibly. We recommend screening of vitamin B6 levels in PD patients, especially those requiring high or increasing doses of carbidopa-levodopa and those with poor nutrition.