Lysosomal enzyme deficiency and GBA mutations in Dystonia

Glucocerebrosidase (GCase) deficiency due to mutations of the glucosidase acid beta ( GBA ) gene causes autosomal-recessive Gaucher’s disease, the most frequent lysosomal storage disorder. Over the past two decades, GBA mutations have been established as the most frequent genetic risk factor to develop Parkinson’s Disease. In dystonia, the underlying aetiology in a relevant proportion of cases remains unknown, hampering the development of causative treatment strategies. Here, we explored the possible role of lysosomal dysfunction in clinical (n=130) and post mortem (n=10) patients with dystonia. As part of extensive diagnostic evaluations (screening for structural, acquired and degenerative causes of dystonia), lysosomal enzyme activity was measured in n=79 retrospectively collected cases of patients with combined dystonia and n=51 prospectively collected cases of patients with cervical dystonia using a clinically validated, fluorescence-based assay. Clinical information on all cases was extensively reviewed and an alternative aetiology of dystonia was identified in n=14 cases on follow-up. Of the remaining n=116 cases of dystonia of unknown origin, complete Sanger Sequencing of GBA exons 1-11 was performed using an established protocol in all n=97 of cases with available DNA. Where there was suspicion based on clinical examination or family history, nigro-striatal degeneration was excluded in n=19 (17.2%) cases with dystonia of unknown origin. Furthermore, lysosomal enzyme activity was measured in different brain regions of age-, sex- and post-mortem delay-matched cases with dystonia of unknown origin (n=10) and healthy controls (n=10) from the Queen Square brain bank. Among cases with dystonia of unknown origin, decreased white cell Glucocerebrosidase activity was measured in a range typical for homozygous (n=2; 1.7%) or heterozygous (n=23; 19.8%) GBA mutation carriers. The frequency of GBA mutations (5/80=6.25%) was significantly higher in patients than in controls (3/257=1.17%) of a historical control group from the same ethnic background (P=0.02; Odds Ratio=5.64, 95% Confidence Interval=1.44 – 21.58) – known pathogenic mutations E326K, T369M and N370S were found. We also identified lower Glucocerebrosidase activity in the cerebellar dentate nucleus (P=0.048) of dystonia patients than healthy controls. This study provides evidence for peripheral and central lysosomal dysfunction in a significant proportion and across the clinical spectrum of dystonia. As in Parkinson’s disease, this was found irrespective of GBA mutation status, indicating a possible role of lysosomal dysfunction as a more general disease mechanism in dystonia. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement This study did not receive dedicated funding ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: The joint UCL/UCLH committees on the Ethics of Human Research - Committee Alpha; REC 07/Q0502/2 All necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines and uploaded the relevant EQUATOR Network research reporting checklist(s) and other pertinent material as supplementary files, if applicable. Yes Individual level data are available upon request from the authors. * b-GAL : beta-Galactosidase CHIT : Chitotriosidase CDN : Cerebellar dentate nucleus CRB : cerebellar cortex CoV : cerebellar cortex GCase : Glucocerebrosidase GBA : glucosidase acid beta GBAP : glucosidase acid beta pseudo-gene PALL : Pallidum SCol : superior colliculus wbc : white blood cell YOPD : young-onset Parkinson’s disease