The Role of Genetic Testing for Parkinson's Disease

Disparities in Genetic Testing for Neurologic Disorders

BACKGROUND AND OBJECTIVES

Genetic testing is now the standard of care for many neurologic conditions. Health care disparities are unfortunately widespread in the US health care system, but disparities in the utilization of genetic testing for neurologic conditions have not been studied. We tested the hypothesis that access to and results of genetic testing vary according to race, ethnicity, sex, socioeconomic status, and insurance status for adults with neurologic conditions.

METHODS

We analyzed retrospective data from patients who underwent genetic evaluation and testing through our institution's neurogenetics program. We tested for differences between demographic groups in 3 steps of a genetic evaluation pathway: (1) attending a neurogenetic evaluation, (2) completing genetic testing, and (3) receiving a diagnostic result. We compared patients on this genetic evaluation pathway with the population of all neurology outpatients at our institution, using univariate and multivariable logistic regression analyses.

RESULTS

Between 2015 and 2022, a total of 128,440 patients were seen in our outpatient neurology clinics and 2,540 patients underwent genetic evaluation. Black patients were less than half as likely as White patients to be evaluated (odds ratio [OR] 0.49, p < 0.001), and this disparity was similar after controlling for other demographic factors in multivariable analysis. Patients from the least wealthy quartile of zip codes were also less likely to be evaluated (OR 0.67, p < 0.001). Among patients who underwent evaluation, there were no disparities in the likelihood of completing genetic testing, nor in the likelihood of a diagnostic result after adjusting for age. Analyses restricted to specific indications for genetic testing supported these findings.

DISCUSSION

We observed unequal utilization of our clinical neurogenetics program for patients from marginalized and minoritized demographic groups, especially Black patients. Among patients who do undergo evaluation, all groups benefit similarly from genetic testing when it is indicated. Understanding and removing barriers to accessing genetic testing will be essential to health care equity and optimal care for all patients with neurologic disorders.

Genetic testing in adults with neurologic disorders: indications, approach, and clinical impacts

The role of genetic testing in neurologic clinical practice has increased dramatically in recent years, driven by research on genetic causes of neurologic disease and increased availability of genetic sequencing technology. Genetic testing is now indicated for adults with a wide range of common neurologic conditions. The potential clinical impacts of a genetic diagnosis are also rapidly expanding, with a growing list of gene-specific treatments and clinical trials, in addition to important implications for prognosis, surveillance, family planning, and diagnostic closure. The goals of this review are to provide practical guidance for clinicians about the role of genetics in their practice and to provide the neuroscience research community with a broad survey of current progress in this field. We aim to answer three questions for the neurologist in practice: Which of my patients need genetic testing? What testing should I order? And how will genetic testing help my patient? We focus on common neurologic disorders and presentations to the neurology clinic. For each condition, we review the most current guidelines and evidence regarding indications for genetic testing, expected diagnostic yield, and recommended testing approach. We also focus on clinical impacts of genetic diagnoses, highlighting a number of gene-specific therapies recently approved for clinical use, and a rapidly expanding landscape of gene-specific clinical trials, many using novel nucleotide-based therapeutic modalities like antisense oligonucleotides and gene transfer. We anticipate that more widespread use of genetic testing will help advance therapeutic development and improve the care, and outcomes, of patients with neurologic conditions.

Prevention of Parkinson's Disease: From Risk Factors to Early Interventions

Parkinson's disease (PD) is a debilitating neurological disorder characterized by progressively worsening motor dysfunction. Currently, available therapies merely alleviate symptoms, and there are no cures. Consequently, some researchers have now shifted their attention to identifying the modifiable risk factors of PD, with the intention of possibly implementing early interventions to prevent the development of PD. Four primary risk factors for PD are discussed including environmental factors (pesticides and heavy metals), lifestyle (physical activity and dietary intake), drug abuse, and individual comorbidities. Additionally, clinical biomarkers, neuroimaging, biochemical biomarkers, and genetic biomarkers could also help to detect prodromal PD. This review compiled available evidence that illustrates the relationship between modifiable risk factors, biomarkers, and PD. In summary, we raise the distinct possibility of preventing PD via early interventions of the modifiable risk factors and early diagnosis.

Genetic Testing in Parkinson's Disease

Genetic testing for persons with Parkinson's disease is becoming increasingly common. Significant gains have been made regarding genetic testing methods, and testing is becoming more readily available in clinical, research, and direct-to-consumer settings. Although the potential utility of clinical testing is expanding, there are currently no proven gene-targeted therapies, but clinical trials are underway. Furthermore, genetic testing practices vary widely, as do knowledge and attitudes of relevant stakeholders. The specter of testing mandates financial, ethical, and physician engagement, and there is a need for guidelines to help navigate the myriad of challenges. However, to develop guidelines, gaps and controversies need to be clearly identified and analyzed. To this end, we first reviewed recent literature and subsequently identified gaps and controversies, some of which were partially addressed in the literature, but many of which are not well delineated or researched. Key gaps and controversies include: (1) Is genetic testing appropriate in symptomatic and asymptomatic individuals without medical actionability? (2) How, if at all, should testing vary based on ethnicity? (3) What are the long-term outcomes of consumer- and research-based genetic testing in presymptomatic PD? (4) What resources are needed for clinical genetic testing, and how is this impacted by models of care and cost-benefit considerations? Addressing these issues will help facilitate the development of consensus and guidelines regarding the approach and access to genetic testing and counseling. This is also needed to guide a multidisciplinary approach that accounts for cultural, geographic, and socioeconomic factors in developing testing guidelines. © 2023 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Elucidating causative gene variants in hereditary Parkinson's disease in the Global Parkinson's Genetics Program (GP2)

The Monogenic Network of the Global Parkinson's Genetics Program (GP2) aims to create an efficient infrastructure to accelerate the identification of novel genetic causes of Parkinson's disease (PD) and to improve our understanding of already identified genetic causes, such as reduced penetrance and variable clinical expressivity of known disease-causing variants. We aim to perform short- and long-read whole-genome sequencing for up to 10,000 patients with parkinsonism. Important features of this project are global involvement and focusing on historically underrepresented populations.

The Genetic Testing Experience of Individuals with Parkinson's Disease

Background

The perspective and experiences of individuals with Parkinson's disease (PD) regarding genetic testing is limited.

Objectives

To determine if anticipated benefits and negative consequences of genetic testing noted in prior studies have occurred in a surveyed group of patients with PD and to identify reasons why some individuals with PD have not had testing.

Methods

Individuals were surveyed from 22 support/advocacy groups throughout the US. Information about patient demographics and genetic testing were assessed, along with the consequences experienced after testing or anticipated by those who have not had testing. Descriptive statistics, Pearson correlation coefficient, ANOVA, and independent sample t-test were utilized for data analysis.

Results

Of the genetic testing group (n = 78), most received testing through a research study (44.9%) or a Direct-to-Consumer company (46.2%). Most did not meet with a genetic counselor before (87.2%) or after testing (64.1%). Fewer positive and fewer negative consequences were reported after testing compared to the consequences anticipated by those who have not undergone testing (P < 0.001, all comparisons). Of the non-genetic testing group (n = 166), 49.4% did not undergo testing because they were not aware it was available and 38.0% because their doctor did not offer it.

Conclusions

Findings demonstrate the need for providers to have genetic testing discussions with PD patients, who may otherwise seek testing via Direct-to-Consumer companies or be unaware it is available. Collaborations with genetic counselors trained in providing anticipatory guidance may assist patients in forming more realistic expectations regarding the consequences experienced after genetic testing for PD.

Environmental and genetic risk factors for Parkinson’s disease

Aim. To analyze risk factors in the group of patients with Parkinson’s disease (PD) and compare them with the literature data.

Materials and methods. The study included 439 patients with PD and 354 controls, comparable by gender and age. For each individual, a registration card was filled in containing demographic, epidemiological, clinical, and neuropsychological data. The severity of the disease was studied according to the MDS-UPDRS scale; the stage of PD was determined according to the Hoehn and Yahr scale. Cognitive functions were assessed by the MoCA test and MMSE. The length of the (CAG)n repeat region in the HTT gene was determined using fragment analysis on the ABI 3730 DNA analyzer. The obtained results were analyzed using GeneMapper Software v4.1 (Applied Biosystems, USA).

Results. When comparing patients with PD and the control group, the odds ratio (OR) for PD in individuals with traumatic brain injury was 3.13 (95% confidence interval (CI): 2,27–4.34; p = 4.94 × 10–13), which showed the significance of this risk factor for PD. Consumption of coffee in the anamnesis distinguished the group of PD patients from the control group (OR = 0.41 (95% CI: 0.30–0.56); p < 0.0001), confirming its neuroprotective effect. Analysis of the variability in the length of the (CAG)n repeat regions in the HTT gene showed that patients whose genotype contained an allele with 17 repeats in combination with any allele other than an allele containing 18 repeats had a protective effect (OR = 0.50 (95% CI: 0.27–0.92); p = 0.025). All genotypes containing an allele with 18 repeats were predisposed to PD (OR = 2.57 (95% CI: 1.66–4.28); p = 0.007). The predisposing effect of the allele to PD, unrelated to the expansion of CAG repeats in the HTT gene, was revealed for the first time.

Conclusion. Traumatic brain injury and the allele with 18 CAG repeats in the HTT gene are risk factors for PD. Coffee consumption can be attributed to protective factors in relation to PD.

Blood-based biomarker in Parkinson's disease: potential for future applications in clinical research and practice

The clinical presentation of Parkinson's disease (PD) is both complex and heterogeneous, and its precise classification often requires an intensive work-up. The differential diagnosis, assessment of disease progression, evaluation of therapeutic responses, or identification of PD subtypes frequently remains uncertain from a clinical point of view. Various tissue- and fluid-based biomarkers are currently being investigated to improve the description of PD. From a clinician's perspective, signatures from blood that are relatively easy to obtain would have great potential for use in clinical practice if they fulfill the necessary requirements as PD biomarker. In this review article, we summarize the knowledge on blood-based PD biomarkers and present both a researcher's and a clinician's perspective on recent developments and potential future applications.

Monogenetic Forms of Parkinson’s Disease – Bridging the Gap Between Genetics and Biomarkers

The therapy of neurodegenerative diseases such as Parkinson’s disease (PD) is still limited to the treatment of symptoms and primarily aimed at compensating for dopaminergic hypofunction. Numerous disease-modifying therapies currently in the pipeline attempt to modify the underlying pathomechanisms. In recent decades, the results of molecular genetics and biomarker research have raised hopes of earlier diagnosis and new neuroprotective therapeutic approaches. As the disease-causing processes in monogenetic forms of PD are better understood than in sporadic PD, these disease subsets are likely to benefit first from disease-modifying therapies. Recent studies have suggested that disease-relevant changes found in genetically linked forms of PD (i.e., PARK-LRRK2, PARK-GBA) can also be reproduced in patients in whom no genetic cause can be found, i.e., those with sporadic PD. It can, therefore, be assumed that as soon as the first causal therapy for genetic forms of PD is approved, more patients with PD will undergo genetic testing and counseling. Regarding future neuroprotective trials in neurodegenerative diseases and objective parameters such as biomarkers with high sensitivity and specificity for the diagnosis and course of the disease are needed. These biomarkers will also serve to monitor treatment success in clinical trials. Promising examples in PD, such as alpha-synuclein species, lysosomal enzymes, markers of amyloid and tau pathology, and neurofilament light chain, are under investigation in blood and CSF. This paper provides an overview of the opportunities and current limitations of monogenetic diagnostic and biomarker research in PD and aims to build a bridge between current knowledge and association with PD genetics and biomarkers.