Assessing the relationship between monoallelic PRKN mutations and Parkinson's risk.

Biallelic Parkin (PRKN) mutations cause autosomal recessive Parkinson's disease (PD); however, the role of monoallelic PRKN mutations as a risk factor for PD remains unclear. We investigated the role of single heterozygous PRKN mutations in three large independent case-control cohorts totalling 10 858 PD cases and 8328 controls. Overall, after exclusion of biallelic carriers, single PRKN mutations were more common in PD than controls conferring a >1.5-fold increase in the risk of PD [P-value (P) = 0.035], with meta-analysis (19 574 PD cases and 468 488 controls) confirming increased risk [Odds ratio (OR) = 1.65, P = 3.69E-07]. Carriers were shown to have significantly younger ages at the onset compared with non-carriers (NeuroX: 56.4 vs. 61.4 years; exome: 38.5 vs. 43.1 years). Stratifying by mutation type, we provide preliminary evidence for a more pathogenic risk profile for single PRKN copy number variant (CNV) carriers compared with single nucleotide variant carriers. Studies that did not assess biallelic PRKN mutations or consist of predominantly early-onset cases may be biasing these estimates, and removal of these resulted in a loss of association (OR = 1.23, P = 0.614; n = 4). Importantly, when we looked for additional CNVs in 30% of PD cases with apparent monoallellic PRKN mutations, we found that 44% had biallelic mutations, suggesting that previous estimates may be influenced by cryptic biallelic mutation status. While this study supports the association of single PRKN mutations with PD, it highlights confounding effects; therefore, caution is needed when interpreting current risk estimates. Together, we demonstrate that comprehensive assessment of biallelic mutation status is essential when elucidating PD risk associated with monoallelic PRKN mutations.

Ambroxol for the Treatment of Patients With Parkinson Disease With and Without Glucocerebrosidase Gene Mutations: A Nonrandomized, Noncontrolled Trial.

Importance: Mutations of the glucocerebrosidase gene, GBA1 (OMIM 606463), are the most important risk factor for Parkinson disease (PD). In vitro and in vivo studies have reported that ambroxol increases ß-glucocerebrosidase (GCase) enzyme activity and reduces α-synuclein levels. These observations support a potential role for ambroxol therapy in modifying a relevant pathogenetic pathway in PD. Objective: To assess safety, tolerability, cerebrospinal fluid (CSF) penetration, and target engagement of ambroxol therapy with GCase in patients with PD with and without GBA1 mutations. Interventions: An escalating dose of oral ambroxol to 1.26 g per day. Design, Setting, and Participants: This single-center open-label noncontrolled clinical trial was conducted between January 11, 2017, and April 25, 2018, at the Leonard Wolfson Experimental Neuroscience Centre, a dedicated clinical research facility and part of the University College London Queen Square Institute of Neurology in London, United Kingdom. Participants were recruited from established databases at the Royal Free London Hospital and National Hospital for Neurology and Neurosurgery in London. Twenty-four patients with moderate PD were evaluated for eligibility, and 23 entered the study. Of those, 18 patients completed the study; 1 patient was excluded (failed lumbar puncture), and 4 patients withdrew (predominantly lumbar puncture-related complications). All data analyses were performed from November 1 to December 14, 2018. Main Outcomes and Measures: Primary outcomes at 186 days were the detection of ambroxol in the CSF and a change in CSF GCase activity. Results: Of the 18 participants (15 men [83.3%]; mean [SD] age, 60.2 [9.7] years) who completed the study, 17 (8 with GBA1 mutations and 9 without GBA1 mutations) were included in the primary analysis. Between days 0 and 186, a 156-ng/mL increase in the level of ambroxol in CSF (lower 95% confidence limit, 129 ng/mL; P < .001) was observed. The CSF GCase activity decreased by 19% (0.059 nmol/mL per hour; 95% CI, -0.115 to -0.002; P = .04). The ambroxol therapy was well tolerated, with no serious adverse events. An increase of 50 pg/mL (13%) in the CSF α-synuclein concentration (95% CI, 14-87; P = .01) and an increase of 88 ng/mol (35%) in the CSF GCase protein levels (95% CI, 40-137; P = .002) were observed. Mean (SD) scores on part 3 of the Movement Disorders Society Unified Parkinson Disease Rating Scale decreased (ie, improved) by 6.8 (7.1) points (95% CI, -10.4 to -3.1; P = .001). These changes were observed in patients with and without GBA1 mutations. Conclusions and Relevance: The study results suggest that ambroxol therapy was safe and well tolerated; CSF penetration and target engagement of ambroxol were achieved, and CSF α-synuclein levels were increased. Placebo-controlled clinical trials are needed to examine whether ambroxol therapy is associated with changes in the natural progression of PD. Trial Registration: ClinicalTrials.gov identifier: NCT02941822; EudraCT identifier: 2015-002571-24.

Genetic analysis of Mendelian mutations in a large UK population-based Parkinson's disease study.

Our objective was to define the prevalence and clinical features of genetic Parkinson's disease in a large UK population-based cohort, the largest multicentre prospective clinico-genetic incident study in the world. We collected demographic data, Movement Disorder Society Unified Parkinson's Disease Rating Scale scores, and Montreal Cognitive Assessment scores. We analysed mutations in PRKN (parkin), PINK1, LRRK2 and SNCA in relation to age at symptom onset, family history and clinical features. Of the 2262 participants recruited to the Tracking Parkinson's study, 424 had young-onset Parkinson's disease (age at onset ≤ 50) and 1799 had late onset Parkinson's disease. A range of methods were used to genotype 2005 patients: 302 young-onset patients were fully genotyped with multiplex ligation-dependent probe amplification and either Sanger and/or exome sequencing; and 1701 late-onset patients were genotyped with the LRRK2 'Kompetitive' allele-specific polymerase chain reaction assay and/or exome sequencing (two patients had missing age at onset). We identified 29 (1.4%) patients carrying pathogenic mutations. Eighteen patients carried the G2019S or R1441C mutations in LRRK2, and one patient carried a heterozygous duplication in SNCA. In PRKN, we identified patients carrying deletions of exons 1, 4 and 5, and P113Xfs, R275W, G430D and R33X. In PINK1, two patients carried deletions in exon 1 and 5, and the W90Xfs point mutation. Eighteen per cent of patients with age at onset ≤30 and 7.4% of patients from large dominant families carried pathogenic Mendelian gene mutations. Of all young-onset patients, 10 (3.3%) carried biallelic mutations in PRKN or PINK1. Across the whole cohort, 18 patients (0.9%) carried pathogenic LRRK2 mutations and one (0.05%) carried an SNCA duplication. There is a significant burden of LRRK2 G2019S in patients with both apparently sporadic and familial disease. In young-onset patients, dominant and recessive mutations were equally common. There were no differences in clinical features between LRRK2 carriers and non-carriers. However, we did find that PRKN and PINK1 mutation carriers have distinctive clinical features compared to young-onset non-carriers, with more postural symptoms at diagnosis and less cognitive impairment, after adjusting for age and disease duration. This supports the idea that there is a distinct clinical profile of PRKN and PINK1-related Parkinson's disease. We estimate that there are approaching 1000 patients with a known genetic aetiology in the UK Parkinson's disease population. A small but significant number of patients carry causal variants in LRRK2, SNCA, PRKN and PINK1 that could potentially be targeted by new therapies, such as LRRK2 inhibitors.

Analysis of the genetic variability in Parkinson's disease from Southern Spain.

To date, a large spectrum of genetic variants has been related to familial and sporadic Parkinson's disease (PD) in diverse populations worldwide. However, very little is known about the genetic landscape of PD in Southern Spain, despite its particular genetic landscape coming from multiple historical migrations. We included 134 PD patients in this study, of which 97 individuals were diagnosed with late-onset sporadic PD (LOPD), 28 with early-onset sporadic PD (EOPD), and 9 with familial PD (FPD). Genetic analysis was performed through a next-generation sequencing panel to screen 8 PD-related genes (LRRK2, SNCA, PARKIN, PINK1, DJ-1, VPS35, GBA, and GCH1) in EOPD and FPD groups and direct Sanger sequencing of GBA exons 8-11 and LRRK2 exons 31 and 41 in the LOPD group. In the EOPD and FPD groups, we identified 11 known pathogenic mutations among 15 patients (40.5%). GBA (E326K, N370S, D409H, L444P) mutations were identified in 7 patients (18.9%); LRRK2 (p.R1441G and p.G2019S) in 3 patients (8.1%); biallelic PARK2 mutations (p.N52fs, p.V56E, p.C212Y) in 4 cases (10.8%) and PINK1 homozygous p.G309D in 1 patient (2.7%). An EOPD patient carried a single PARK2 heterozygous mutation (p.R402C), and another had a novel heterozygous mutation in VPS35 (p.R32S), both of unknown significance. Moreover, pathogenic mutations in GBA (E326K, T369M, N370S, D409H, L444P) and LRRK2 (p.R1441G and p.G2019S) were identified in 13 patients (13.4%) and 4 patients (4.1%), respectively, in the LOPD group. A large number of known pathogenic mutations related to PD have been identified. In particular, GBA and LRRK2 mutations appear to be considerably frequent in our population, suggesting a strong Jewish influence. Further research is needed to study the contribution of the novel found mutation p.R32S in VPS35 to the pathogenesis of PD.

A 6.4 Mb duplication of the α-synuclein locus causing frontotemporal dementia and Parkinsonism: phenotype-genotype correlations.

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.

C9orf72 expansions are the most common genetic cause of Huntington disease phenocopies.

OBJECTIVE: In many cases where Huntington disease (HD) is suspected, the genetic test for HD is negative: these are known as HD phenocopies. A repeat expansion in the C9orf72 gene has recently been identified as a major cause of familial and sporadic frontotemporal lobar degeneration and amyotrophic lateral sclerosis. Our objective was to determine whether this mutation causes HD phenocopies. METHODS: A cohort of 514 HD phenocopy patients were analyzed for the C9orf72 expansion using repeat primed PCR. In cases where the expansion was found, Southern hybridization was performed to determine expansion size. Clinical case notes were reviewed to determine the phenotype of expansion-positive cases. RESULTS: Ten subjects (1.95%) had the expansion, making it the most common identified genetic cause of HD phenocopy presentations. The size of expansion was not significantly different from that associated with other clinical presentations of C9orf72 expanded cases. The C9orf72 expansion-positive subjects were characterized by the presence of movement disorders, including dystonia, chorea, myoclonus, tremor, and rigidity. Furthermore, the age at onset in this cohort was lower than previously reported for subjects with the C9orf72 expansion and included one case with pediatric onset. DISCUSSION: This study extends the known phenotype of the C9orf72 expansion in both age at onset and movement disorder symptoms. We propose a revised clinico-genetic algorithm for the investigation of HD phenocopy patients based on these data.