Movement disorders in 2020: clinical trials, genetic discoveries, and COVID-19
Authors: Eng-King Tan
Journal: The Lancet Neurology (2020)

With 2020 hindsight, this has been an extraordinary year not just for patients with movement disorders but also for every individual around the world, due to the impact of the COVID-19 pandemic. Several studies investigating the effect of COVID-19 on individuals with Parkinson's disease have suggested that parkinsonian symptoms worsened among those who were infected, that those with more advanced Parkinson's disease were at increased risk of pulmonary compromise, that hospitalised patients with Parkinson's disease and COVID-19 appeared to have a heightened mortality rate, and that patients with Parkinson's disease showed more stress, depressive symptoms, and anxiety during the lockdown period than before this period.1Tan EK Albanese A Chaudhuri K et al.Adapting to post-COVID19 research in Parkinson's disease: lessons from a multinational experience.Parkinsonism Relat Disord. 2020; (published Oct 7.)https://doi.org/10.1016/j.parkreldis.2020.10.009Summary Full Text Full Text PDF Scopus (7) Google Scholar A case report linking severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection with new-onset Parkinson's disease has led to an increased awareness of this potential association and also its underlying biological plausibility.2Cohen ME Eichel R Steiner-Birmanns B et al.A case of probable Parkinson's disease after SARS-CoV-2 infection.Lancet Neurol. 2020; 19: 804-805Summary Full Text Full Text PDF PubMed Scopus (146) Google Scholar Amid the pandemic, several clinical safety and proof-of-concept trials have taken small steps towards identifying disease-modifying therapies. Targeting α-synuclein, either through active or passive immunisations, gained considerable attention in the past few years for its potential for slowing down neurodegeneration, as dysfunction of the protein is a major driver of neurodegeneration. In a first-in-human phase 1 randomised study of subcutaneous immunisations with PD01A (ie, an active immunotherapy using a short peptide directed at oligomeric α-synuclein), 21 of the original 24 patients completed all the initial and booster immunisations over more than 4 years of follow-up.3Volc D Poewe W Kutzelnigg A et al.Safety and immunogenicity of the α-synuclein active immunotherapeutic PD01A in patients with Parkinson's disease: a randomised, single-blinded, phase 1 trial.Lancet Neurol. 2020; 19: 591-600Summary Full Text Full Text PDF PubMed Scopus (83) Google Scholar The immunisation led to an increase in antibody titres with neither imaging evidence of neuroinflammation nor significant clinical adverse effects, providing impetus for investigators to proceed to the next phase of the study. Loss-of-function mutations in the glucocerebrosidase gene that encodes lysosomal β-glucocerebrosidase (GCase) represent an important risk factor for Parkinson's disease, and can lead to α-synuclein accumulation. Ambroxol, a secretolytic agent used in the treatment of respiratory diseases, increases GCase activity and hence reduces α-synuclein. In an open-label study using an escalating dose of oral ambroxol, 18 of the 23 patients with moderately severe Parkinson's disease completed the study.4Mullin S Smith L Lee K et al.Ambroxol for the treatment of patients with Parkinson disease with and without glucocerebrosidase gene mutations: a nonrandomized, noncontrolled trial.JAMA Neurol. 2020; 77: 427-434Crossref PubMed Scopus (198) Google Scholar Ambroxol was well tolerated and detected in the CSF, with an increase in CSF GCase activity. Although an improvement in the clinical motor scores was suggested with the drug, future randomised controlled trials will be required to show its effect on motor progression. Subcutaneous injection or infusion of apomorphine (a non-selective dopamine agonist) via mini pumps has been used in patients with advanced Parkinson's disease to relieve off states. Alternative routes of delivery of apomorphine have now been investigated. A multicentre, randomised, double-blind study in patients with Parkinson's disease and more than 2 h off time per day compared an effective dose of apomorphine sublingual film individually titrated to 10–35 mg with a placebo (54 vs 55 patients).5Olanow CW Factor SA Espay AJ et al.Apomorphine sublingual film for off episodes in Parkinson's disease: a randomised, double-blind, placebo-controlled phase 3 study.Lancet Neurol. 2020; 19: 135-144Summary Full Text Full Text PDF PubMed Scopus (83) Google Scholar There was a significantly better improvement in the Movement Disorder Society-Unified Parkinson Disease Rating Scale motor scores (from pre-dose to 30 min post-dose) at week 12 in participants receiving apomorphine than in those receiving placebo. 31% of participants who were on the drug reported mild-to-moderate oropharyngeal side-effects, with 17% discontinuing the treatment. The long-term safety and efficacy of this apomorphine formulation as an on-demand therapy for off episodes in patients with Parkinson's disease still needs to be further evaluated. Repurposing of drugs continues to attract interest as this strategy can potentially reduce the time frame and cost and improve regulatory support for successful clinical translation. Nilotinib has been used to treat chronic myeloid leukaemia. In a single-centre, double-blind, placebo-controlled phase 2 trial, 75 patients with moderately severe Parkinson's disease were randomised into placebo, nilotinib (150 mg), or nilotinib (300 mg) groups (daily oral administration for a year).6Pagan FL Hebron ML Wilmarth B et al.Nilotinib effects on safety, tolerability, and potential biomarkers in Parkinson disease: a phase 2 randomized clinical trial.JAMA Neurol. 2020; 77: 309-317Crossref PubMed Scopus (103) Google Scholar Although there were more adverse side effects in the nilotinib groups than in the placebo group, the drug was generally safe and detectable in CSF. The concentrations of some metabolic markers and specific proteins (such as α-synuclein oligomers and hyperphosphorylated tau) in CSF were altered in those on nilotinib, raising the possibility that these can be used as potential biomarkers of drug response in future phase 3 trials. Next generation sequencing approaches to unravel underlying genetic causes of rare movement disorders can provide definitive diagnosis and facilitate pathophysiological studies to identify novel therapeutic targets. To unravel the monogenic causes of dystonia (a clinically and genetically heterogeneous disease), whole exome sequencing was done in 764 patients with dystonia and 346 healthy parents in an international collaborative study involving 33 centres.7Zech M Jech R Boesch S et al.Monogenic variants in dystonia: an exome-wide sequencing study.Lancet Neurol. 2020; 19: 908-918Summary Full Text Full Text PDF PubMed Scopus (118) Google Scholar The authors managed to identify causative or probable causative gene variants in 135 (19%) of the 728 families, and diagnostic variants in 11 genes not previously linked to dystonia. Most of the identified variants are in genes that are linked to neurodevelopmental disorders. In essence, the application of exome sequencing in a collective large number of patients with dystonia improves diagnosis, facilitates genotype–phenotype correlation, potentially guides genetic testing, and improves the clinical management of patients with dystonia. Repeat expansion disorders have been linked to a wide clinical phenotype. One study examined 100 genetically confirmed carriers of cerebellar ataxia with neuropathy and vestibular areflexia syndrome, which is due to biallelic repeat expansions in RFC1 (replication factor complex subunit 1).8Cortese A Tozza S Yau WY et al.Cerebellar ataxia, neuropathy, vestibular areflexia syndrome due to RFC1 repeat expansion.Brain. 2020; 143: 480-490Crossref PubMed Scopus (127) Google Scholar The investigators found that a dry spasmodic cough is commonly associated with repeat expansion disorders, and that sensory neuropathy was the only manifestation in some patients,8Cortese A Tozza S Yau WY et al.Cerebellar ataxia, neuropathy, vestibular areflexia syndrome due to RFC1 repeat expansion.Brain. 2020; 143: 480-490Crossref PubMed Scopus (127) Google Scholar although other investigators have reported RFC1 mutations in multiple system atrophy.9Wan L Chen Z Wan N et al.Biallelic intronic AAGGG expansion of RFC1 is related to multiple system atrophy.Ann Neurol. 2020; (published online Sept 16.)https://doi.org/10.1002/ana.25902Crossref PubMed Scopus (39) Google Scholar Similarly, GGC repeat expansions in NOTCH2NLC, which causes neuronal intranuclear inclusion disease, have now been reported in patients with Parkinson's disease and essential tremor who do not show cognitive dysfunction or imaging evidence of intranuclear inclusion disease.10Ma D Tan YJ Ng ASL et al.Association of NOTCH2NLC repeat expansions with Parkinson disease.JAMA Neurol. 2020; (published online Aug 24.)https://doi.org/10.1001/jamaneurol.2020.3023Crossref Scopus (63) Google Scholar A high index of suspicion and awareness is needed for appropriate genetic testing in patients who present with movement disorders. I declare that I have received honoraria from Elsevier and Wiley for editorial duties.