Summary: Mutations in the GBA gene, a recognized risk factor for Parkinson’s disease, also strongly influence the risk and pace of cognitive decline, a new multi‑center study reports.
Source: Brigham and Women’s Hospital.
GBA gene mutations linked to faster memory loss in Parkinson’s patients, opening the way for targeted clinical trials
Parkinson’s disease (PD) is classically defined by motor symptoms such as tremor, slowed movement and stiffness. Yet cognitive impairment and dementia increasingly determine patients’ quality of life and caregiver burden. New research from the Ann Romney Center for Neurological Diseases at Brigham and Women’s Hospital shows that certain mutations in the glucocerebrosidase gene (GBA) not only increase PD risk but also accelerate cognitive decline once Parkinson’s has developed. The study, led by Clemens R. Scherzer, MD, and collaborators across North America and Europe, was published in the Annals of Neurology.
“This work marks an important step toward personalized medicine in Parkinson’s disease,” said Clemens Scherzer, associate professor of Neurology and head of the Neurogenomics Lab and Parkinson Personalized Medicine Initiative at Brigham and Women’s Hospital and Harvard Medical School. “By identifying specific genetic drivers of cognitive progression, we can design smaller, more efficient clinical trials that match molecular therapies to the patients most likely to benefit.”
Two defective copies of GBA cause Gaucher’s disease, a rare inherited disorder that can produce severe neurologic complications in childhood. One defective copy was long thought to be clinically insignificant, but research over the past decade has established heterozygous GBA mutations as a common genetic risk factor for Parkinson’s disease. The new international analysis clarifies that not all GBA variants carry the same risk for cognitive decline.
The team analyzed data from 2,304 people with Parkinson’s disease across seven longitudinal cohorts in the United States, Canada and Europe, with up to 12.8 years of follow‑up (median 4.1 years) and 20,868 clinical visits. Overall, 10.3 percent of sequenced patients carried at least one GBA mutation. The investigators categorized variants into neuropathic Gaucher’s (severe) mutations, complex alleles, the common non‑neuropathic N370S mutation, and nonpathogenic risk variants, and then compared rates of global cognitive impairment and scores on the Mini–Mental State Exam (MMSE).
Key findings included:
- Patients with neuropathic GBA mutations (about 1.4% of the cohort) faced the highest risk of developing global cognitive impairment. Their hazard ratio for cognitive decline was 3.17 (95% CI, 1.60–6.25) compared with noncarriers, and they showed a significantly faster drop in MMSE scores (p = 0.0009).
- Carriers of complex GBA alleles (about 0.7% of patients) also had a markedly increased risk (HR 3.22; 95% CI, 1.18–8.73; p = 0.022).
- The common non‑neuropathic N370S mutation and more benign risk variants did not reach statistical significance for accelerated cognitive decline in this analysis.
The study reports that roughly half of PD patients carrying a neuropathic GBA mutation developed global cognitive impairment within ten years of Parkinson’s diagnosis, compared with about 20 percent of patients without GBA mutations. These differences suggest that specific, pathogenic GBA variants shift the trajectory of cognitive decline into “high gear.”
Because enzyme replacement and other therapies already exist for Gaucher’s disease, the investigators argue that molecularly targeted, GBA‑directed clinical trials in Parkinson’s are now feasible. Scherzer and colleagues estimate that trials focused on the highest‑risk genetic subgroup would require far fewer participants—potentially reducing sample sizes roughly 25‑fold relative to conventional, unstratified designs—lowering costs and improving the chances of detecting benefit.
Past clinical trials aimed at slowing Parkinson’s progression have frequently been inconclusive or unsuccessful. The authors suggest that a contributing factor has been heterogeneous trial populations in which molecular drivers of progression, like specific GBA mutations, were not accounted for. By providing a toolkit of genetic tests, biomarkers and clinical parameters, the research team and partners hope to enable smaller proof‑of‑concept trials that are better matched to the underlying biology of subgroups of patients.
To advance these goals, Scherzer reports the launch of a consortium with The Michael J. Fox Foundation and industry collaborators to develop an open toolkit for GBA‑targeted trials in Parkinson’s disease. The toolkit is intended as a shared resource for academic investigators and pharmaceutical companies and will include standardized gene testing approaches, biomarker panels, and recommended clinical outcome measures for molecularly targeted studies.
Funding: The study received support from The Michael J. Fox Foundation; the National Institutes of Health; Harvard NeuroDiscovery Center; the U.S. Department of Defense; M.E.M.O. Hoffman Foundation; Parkinson’s Disease Foundation; Wellcome Trust; Medical Research Council (MRC); Parkinson’s UK; Cure‑PD; Patrick Berthoud Trust; Van Geest Foundation; Stichting Alkemade‑Keuls; Stichting ParkinsonFonds; NIHR; Assistance Publique Hôpitaux de Paris; French clinical research hospital program (PHRC); “Investissements d’Avenir”; Prinses Beatrix Fonds; and related philanthropic sources.
Source: Elaine St. Peter, Brigham and Women’s Hospital.
Image Source: Public domain image attributed to NeuroscienceNews.com.
Original Research: “Specifically neuropathic Gaucher’s mutations accelerate cognitive decline in Parkinson’s” by Ganqiang Liu, Brendon Boot, Joseph J. Locascio, Iris E. Jansen, Sophie Winder‑Rhodes, Shirley Eberly, Alexis Elbaz, Alexis Brice, Bernard Ravina, Jacobus J. van Hilten, Florence Cormier‑Dequaire, Jean‑Christophe Corvol, Roger A. Barker, Peter Heutink, Johan Marinus, Caroline H. Williams‑Gray, Clemens R. Scherzer and the International Genetics of Parkinson Disease Progression (IGPP) Consortium; Annals of Neurology. Published online November 18, 2016. DOI: 10.1002/ana.24781.
Abstract
Specifically neuropathic Gaucher’s mutations accelerate cognitive decline in Parkinson’s
Objective
The investigators tested the hypothesis that GBA mutations known to cause neuropathic Gaucher’s disease in homozygotes produce a particularly aggressive pattern of cognitive decline when present in heterozygous Parkinson’s patients, whereas non‑neuropathic mutations have more moderate effects.
Methods
Data from 2,304 Parkinson’s patients, with 20,868 longitudinal visits (follow‑up up to 12.8 years; median 4.1 years) across seven cohorts, were analyzed. The study evaluated four classes of GBA variation and their differential effects on cognitive decline using mixed effects models and Cox proportional hazards analysis.
Results
In this sample, 10.3% of patients with GBA sequencing carried a mutation. Neuropathic Gaucher’s mutations (1.4% of patients) were associated with a hazard ratio of 3.17 (95% CI, 1.60–6.25) for global cognitive impairment and with significantly faster MMSE decline (p = 0.0009). Complex GBA alleles (0.7%) showed a similar elevated risk (HR 3.22; 95% CI, 1.18–8.73; p = 0.022). The common non‑neuropathic N370S mutation (1.5%) and nonpathogenic risk variants (6.6%) did not reach statistical significance in this analysis.
Interpretation
GBA mutations that are pathogenic for neuropathic Gaucher’s disease and complex alleles substantially accelerate longitudinal cognitive decline in Parkinson’s disease. These genotype‑specific differences have direct implications for designing more efficient, molecularly targeted clinical trials for cognitive outcomes in PD. Ann Neurol 2016;80:674–685.